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Cancer is an important cause of morbidity and avoidable mortality for Māori, with more than a quarter of all deaths among Māori attributable to this disease.1 There is substantial evidence of enduring disparities in cancer incidence, mortality and survival between Māori and non-Māori, with cancer making an important contribution to the life expectancy gap between these groups.2

Our country’s new Cancer Action Plan for the years 2019–2029 aims to address inequities in the burden of cancer experienced by Māori New Zealanders.3 In the plan, the Ministry of Health stated that the plan would be equity-led, achieve equity by design, and included as a primary outcome that “New Zealanders experience equitable cancer outcomes”. These objectives are important and signal a commitment from central Government to closing the cancer gap for Māori.

Given the substantial inequities in cancer outcomes experienced by Māori, the prioritisation of initiatives to close this gap is congruent with the objectives of the new Plan. However, in the presence of finite capital (both fiscal and political), there is a need to carefully set priorities that reflect the reality of the cancer burden faced by Māori. While many initiatives will have pan cancer impact—such as renewed investment in the Māori cancer care workforce—there is value in understanding which cancers cause the largest burden on Māori, before we prioritise and invest in new initiatives that may increase inequities, or only impact one or two cancers (such as screening programmes).

In this manuscript, we present current evidence on the most commonly diagnosed cancers among Māori between 2007–2016, the decade immediately following on from the 1996–2006 period presented in the landmark Unequal Impact II report.2 We also present the most common causes of cancer death for Māori over this period. Alongside these absolute cancer death data, we present a relative cancer survival comparison between Māori and non-Māori. Finally, we summarise the factors that link these cancers, and discuss how to reduce their occurrence and the overall cancer mortality burden for Māori.

What are the most commonly diagnosed cancers among Māori?

Using New Zealand Cancer Registry data, we determined the 10 most commonly diagnosed cancers among Māori between 2007–2016, calculated age- and sex-standardised incidence rates (SIR), and also calculated standardised rate differences (SRD) to compare incidence between Māori and non-Māori. We determined incidence rates and rate differences for both the total population (Figure 1) and separately for males and females (Appendix Figure 1).

Figure 1: Age- and sex-standardised incidence rate (SIR) and absolute numbers of annual cases for the top 10 most commonly diagnosed cancers for Māori between 2007–2016 (top), along with the age- and sex-standardised rate difference (SRD) between Māori and Non-Māori (bottom). Analysis methods are described in the Appendix. Data is direct age- and sex-standardised to the 2001 total Māori population.

In terms of absolute numbers of cases, lung cancer was the most commonly diagnosed cancer among Māori with 401 cases/year, followed by breast (373/year), prostate (190/year) and colorectal (170 cases/year). In terms of age- and sex-standardised incidence rates, breast (SIR: 45/100,000 Māori per year) and lung (42/100,000) were highest, followed by prostate (20/100,000) and colorectal (18/100,000). The remainder of the top 10 (stomach, uterine, liver, pancreatic, and the blood cancers leukaemia and non-Hodgkin’s lymphoma) clustered around 6–10 cases/100,000 Māori. For Māori females, the most commonly diagnosed cancer was breast (88/100,000 Māori females), followed by lung (46/100,000) and colorectal cancers (17/100,000). For Māori males, the most commonly diagnosed cancer was prostate (46/100,000 Māori males), followed by lung (43/100,000) and colorectal cancers (23/100,000).

In comparison with non-Māori, Māori were more likely to be diagnosed with most of these cancers than non-Māori, particularly lung (SRD: females absolute difference of 34 cases per 100,000, males 28/100,000, total 29/100,000), but less likely to be diagnosed with colorectal (females -4/100,000, males -4/100,000, total -4/100,000) and prostate cancers (males -11/100,000).

What are the most common causes of cancer death for Māori?

Mortality

Using New Zealand Mortality Collection data, we determined the 10 most common causes of cancer death among Māori between 2007–2016, calculated age- and sex-standardised mortality rates (SMR), and also calculated standardised rate differences to compare mortality between Māori and non-Māori (SRD). Like incidence, we determined mortality rates and rate differences for both the total population (Figure 2) and separately for males and females (Appendix Figure 2).

Lung cancer was the most common cause of cancer death among Māori, with 311 deaths/year (SMR: 32/100,000). This was followed by breast (77 deaths/year, 9/100,000 Māori) and colorectal cancers (68 deaths/year, 7/100,000). The remainder of the top 10 (stomach, liver, pancreatic, ill-defined, prostate, leukaemia and non-Hodgkin’s lymphoma) caused between 20–50 deaths per year (2–6/100,000). The most common cause of cancer death among Māori females was lung (34/100,000 females), followed by breast (17/100,000) and colorectal cancers (6/100,000). The most common cause of cancer death among Māori males was lung (34/100,000 Māori males), followed by colorectal (10/100,000) and prostate cancers (9/100,000).

In comparison with non-Māori, Māori were more likely to die from most of these cancers than non-Māori, particularly lung (SRD: absolute difference in rates for females 25/100,000, males 22/100,000, total 23/100,000), although differences for colorectal cancer were negligible (females -2/100,000, males 0/100,000, total -1/100,000).

There is obvious crossover between the incidence and mortality figures presented above, with nine of the top 10 cancers occurring on both lists. Cancer mortality is of course intrinsically linked to cancer incidence: the more common a cancer is, the more common that death from that cancer will be. As such, many cancer deaths are avoidable via prevention of cancer incidence; but many cancer deaths are also avoidable via improvements in the likelihood of survival following a cancer diagnosis. Like incidence, cancer survival is a factor which is not equal between Māori and non-Māori.2

Survival

In Figure 3, we have plotted the absolute number of cancer deaths among Māori per year (y-axis) against the relative disparity in cancer survival (ie, post-diagnosis survival) between Māori and non-Māori (x-axis). This figure helps us to contextualise relative disparities in cancer survival against the actual absolute mortality burden experienced by Māori. For example, the strongest observed survival disparity is found for melanoma (age-sex-adjusted hazard ratio [HR]: 2.6, 95% CI 2.0–3.3), but fewer than six Māori died of this cancer per year over the study period (5.9 deaths/year). Contrast this with lung cancer, for which the survival disparity is smaller (HR: 1.3, 95% CI 1.2–1.4) but the mortality burden is much higher (311 Māori deaths/year). Importantly, survival is poorer for Māori compared to non-Māori for each of the top 10 causes of Māori cancer death, with adjusted hazard ratios ranging from 1.1 (pancreatic cancer) to 2.1 (prostate cancer). A complete list of hazard ratios for all cancers, for both the total combined population and stratified by sex, are presented in Appendix Table 2.

Figure 3: Scatterplot showing the average annual cancer-specific deaths among Māori (2007–2016) versus cancer-specific mortality hazard ratios (Māori vs Non-Māori), for a) all cancers including lung cancer; and b) all cancers excluding lung cancer. Only cancers where at least five cancer deaths occurred per year are plotted. Analysis methods are described in the Appendix. HRs are presented on the logarithmic scale.

What is happening over time?

Investigating temporal trends in incidence, mortality and survival can help us to understand whether (or not) we are making progress in achieving better cancer outcomes for Māori. In Figure 4, we present the age-sex-standardised incidence, mortality and rate differences for each year between 2007–2016. We have focused on lung cancer as both the most commonly diagnosed and most common cause of cancer death for Māori men and women.

Figure 4: Lung cancer age-sex-standardised incidence rate and rate difference (top), mortality rate and rate difference (middle), and differences in survival between Māori and non-Māori (bottom) over the 2007–2016 period. For the survival analysis, shaded areas indicate 95% confidence intervals. (Note: the observed abrupt increase in recorded lung cancer deaths in 2015 is unexplained, and we are investigating this with National Collections.)

From Figure 4 we observe that, for the most common cause of cancer and cancer death for Māori (lung cancer), both incidence and mortality appear to be reducing over time—along with the disparities between Māori and non-Māori for these measures. However, disparities in lung cancer survival for Māori compared to non-Māori have remained relatively unchanged over the previous decade, ranging between 20–40% excess mortality with no clear temporal trend in either direction (Figure 4).

How do we reduce the cancer burden for Māori?

The factors underpinning overall worse cancer incidence, mortality and survival for Māori are systemic. These outcomes are driven by inequities in the social determinants of good health, determinants that are structural in nature and not controlled by Māori (just as they are not controlled by other indigenous and minority populations around the world).4 In the context of cancer, these determinants combine to increase Māori exposure to carcinogens, to prevent access to screening and early detection, and to prevent timely access to best-practice curative treatment. These factors occur across cancers, and the extent to which they impact on outcomes will depend on the unique characteristics of each cancer.

A systems-level problem requires system-level solutions. Broad health system actions that impact multiple cancers—such as improving access for Māori to timely diagnosis and appropriate treatment, regardless of income or place of residence—are crucial. Likewise, enhancing Māori access to cancer control decision-making, coupled with the resources required to improve cancer prevention, early detection, treatment and support for Māori-led approaches to providing these services, are also vital. While these broad actions are necessary, dismantling the barriers to equitable cancer outcomes for Māori will require a cancer-specific approach in some instances. In an absolute sense, the cancers identified in Figures 1 and 2 have the most profound impact on overall cancer mortality for Māori. However, systemic actions to reduce Māori cancer deaths should not necessarily be prioritised towards cancers in order of burden. To be effective, such prioritisation must take into account factors such as preventability of the cancer, ability to detect the cancer at an early stage, prognosis of the cancer once it is detected, and the availability of curative treatment options within a given cancer context.

Prevention

More than half of the top 10 most common cancers among Māori (Figure 1) and the top 10 most common causes of cancer death for Māori (Figure 2) have known key aetiological exposures that disproportionately impact Māori compared to non-Māori. These exposures can be broadly grouped as tobacco exposure (lung5 and pancreatic6 cancers), infectious diseases (stomach7 and liver8 cancers9), diet and obesity/diabetes mellitus (breast,10 uterine,10 colorectal10 and pancreatic6 cancers) and familial genetic predisposition (stomach cancer11). Māori are substantially more likely to be exposed to tobacco,12 to be exposed to infection with Helicobacter pylori7 and the Hepatitis virus,13 and to be exposed to the structural causes of obesity and diabetes.14

The relative contribution of each of these known exposures to the incidence of a given cancer varies depending on the context. The attributable fraction of lung cancer cases caused by tobacco exposure has been estimated to be between 80–90%.15,16 More than a third of uterine cancers are attributable to obesity.10 More than two-thirds of all stomach cancers are attributable to Helicobacter pylori infection, with this bacterium responsible for 90% of non-cardia stomach cancers—the most common form of stomach cancer diagnosed among Māori.17 Nearly 40% of all liver cancers worldwide are attributable to the hepatitis B or C virus,9 and 70% of Māori liver cancer patients will have a history of hepatitis B or C infection, suggesting a much higher attributable fraction for Māori than the international average.18 In Australia and New Zealand an estimated 17% of pancreatic cancer cases are attributable to high fasting plasma glucose (consistent with pre- or established diabetes mellitus), around the same as that attributable to tobacco exposure.6

Thus, a substantial proportion of the most common causes of cancer and cancer death for Māori are attributable to known preventable exposures. We can draw hope and encouragement from the knowledge that the means of preventing a substantial proportion of cancers for Māori are within our grasp—and include steadfast commitment to Smokefree 2025 (with a stronger focus on smoking in Māori), exploration of Helicobacter pylori test-and-treat programmes, revived vigour in (and monitoring of) our hepatitis vaccination and surveillance programmes, and a regulatory commitment to ensuring that nutritious and healthy lifestyles are accessible and affordable for all (particularly Māori). This hope must be accompanied with renewed determination and innovation to make these tools work for Māori. National cancer prevention policies should combine a population-based and underserved population approach—known as proportionate universalism19—and emphasis on the factors outlined here is consistent with this approach. Perhaps most crucially, an approach that focuses resources on the prevention of cancers that have the strongest impact on Māori is consistent with the principles of the Treaty of Waitangi, which require the Crown to take active measures to restore balance in situations where Māori have been disadvantaged.20

Reducing Māori cancer deaths

Five of the top 10 causes of cancer death for Māori (lung, stomach, pancreas, liver, ill-defined) have an expected one-year survival of less than 50%, with the most common cause (lung) having a one-year survival of approximately 35% for both Māori and non-Māori (data not shown). The nature of tumour development within these cancer types means that disease detection often does not occur until tumours have metastasised, at which point the benefit of a curative therapeutic approach is questionable. More than two-thirds of all Māori cancer deaths each year occur among these poor-prognosis cancers (Figure 2).

With this in mind, the primary key to reducing cancer deaths for Māori is by preventing the cancer in the first place (see above). If prevention is unsuccessful, then the next highest priority is early detection, when curative treatment is still possible. Once the cancer is diagnosed, the highest priority becomes ensuring access to timely best-practice treatment for the given tumour type and sub-type. Unfortunately, there is evidence that Māori are underserved in each of these post-diagnosis priorities.21,22 There are some burgeoning examples of high Māori screening participation in some regions (eg, the Southern DHB bowel screening programme), and these successes should be examined, documented and modeled where appropriate.

Early detection and screening

Early detection of primary lung cancer currently relies on either presentation of a patient with respiratory symptoms, or on chance findings following examination for other conditions (eg, chest x-ray for suspected heart disease). Given the poor prognosis of lung cancer, detection of tumours at the asymptomatic stage may increase the chances of survival via curative treatment. Studies investigating the efficacy of lung cancer screening via computed tomography (CT) scan have been promising.23–25 Preparatory lung cancer screening work is currently being completed in various locations throughout New Zealand, with the results of this preparatory work of critical importance to Māori health. National screening programmes for breast and colorectal cancers—both in the top three most common causes of cancer death for Māori—are in operation, although the latter programme is in its infancy and as of January 2020 was operational in 10 of the 20 district health boards.26 With evidence that Māori have poorer access to national screening programmes than non-Māori,27,28 there is an urgent need for renewed prioritisation and vigour in maximising Māori participation across these programmes.

Many of the most commonly diagnosed cancers among Māori are diagnosed outside of screening programmes. Diagnosis of these cancers principally relies on detection through primary care, although there is evidence that Māori are more likely to be diagnosed following acute admission at an emergency department.29 Maximising early diagnosis of cancers for Māori requires us to consider the key barriers to early diagnosis that Māori (to a greater extent than non-Māori) face. These include the financial burden of general practitioner visits, transport and travel, as well as other factors including patient comorbidity that may complicate diagnosis.30 In essence, we need to recognise that our current means of early detection systemically disadvantages Māori, and that this disadvantage contributes to the perpetuation of inequities in cancer death between Māori and non-Māori.

In terms of specific actions that impact on the cancers in Figures 1 and 2, the pathways for achieving important health gain for Māori will vary depending on the cancer. For example, an important pathway in terms of early detection of liver cancer for Māori is hepatitis surveillance. As noted above, hepatitis B and C appear to be the primary causes of liver cancer for Māori; however, Māori are underserved by the current national hepatitis surveillance programme. We previously observed that, in a cohort of Māori liver cancer patients with hepatitis B or C, only around 40% were on surveillance.31 Crucially, more than three-quarters (77%) of those not on surveillance were diagnosed with stage III or later disease, compared to 33% of those who were on surveillance.31 These observations, echoes of which can be observed across cancers, strongly suggest that careful scrutiny of the barriers to hepatitis surveillance could yield important health gains for Māori with liver disease.

Access to best-practice and timely treatment

There is compelling evidence that Māori have poorer access to timely best-practice treatment compared to non-Māori.21 For example, Stevens et al32 observed that Māori lung cancer patients were 60% less likely to be referred to a medical oncologist than non-Māori and were 70% less likely to receive curative treatment. Because we know that Māori have generally poorer access to best-practice and timely care, cancer care services have an important role to play in reducing the cancer burden for Māori.

In their global report on the drivers of social inequalities in cancer outcomes, the International Agency for Research on Cancer (IARC)4 summarised the key drivers of equitable access to cancer care as the following three A’s:

Availability: The physical availability of high-quality cancer care services, how well resourced and managed these services are, and how well they communicate with patients.

Affordability: The financial accessibility of the cancer treatment journey, from the costs of care to travel/transportation and loss of income.

Acceptability: How cancer care services are perceived by population groups, in terms of factors including effectiveness of care (ie, whether the care will actually work) and cultural competency of the system (ie, how similar/dissimilar the system is to your own culture).4

We can identify our own system within these three A’s, and how these are likely to be contributing to poorer cancer outcomes for Māori. Relevant factors include where services are located relative to where Māori live, the reality that some best-practice treatments are only available if privately funded, the inflexible nature of pathways of cancer care that do not necessarily reflect the priorities of Māori, and inadequate resourcing of Māori treatment providers and navigators.33 Each of these factors (and others) are important sources of disparities in access to care and poor cancer outcomes for Māori, and will be occurring to a different extent across cancer types. Underpinning the receipt of best-practice and timely care by Māori is the existence of standards of care (such as those recently published for colorectal cancer34) that clearly benchmark what a patient should expect to receive during their cancer care, and an unerring apolitical commitment to ensuring these standards are met for Māori across all district health boards in New Zealand.

Other opportunities for improvements in cancer outcomes for Māori

While we have focused in this manuscript on the cancers that present the greatest overall cancer burden on Māori, this does not detract from the importance of cancers that may be less common but will have equal impact at an individual (and whānau) level. For example, while the number of Māori female deaths from cervical cancer (11/year; Appendix Table 1) is far fewer than lung or breast cancers, the large survival disparity between Māori and non-Māori (adjusted HR: 1.4, 95% CI 1.1–1.8) suggests that there is room within existing systems for substantial improvement that will save the lives of Māori women. The advent self-testing kits for human Papilloma virus (HPV, the cause of all cases of cervical cancer9) will likely increase the uptake of cervical screening among those who did not previously access this screening.35 This is important, and might address the current substantial disparity in access to the national cervical screening programme among screen-age Māori women (64%) compared to European women (81%).28 Resourcing of cancer control initiatives aimed at reducing the cancer burden for Māori must take into account the burden of a given cancer, as outlined throughout this manuscript—but they must also remain flexible to ensure that we do not miss opportunities for relatively straightforward interventions (such as HPV self-testing) that will invariably save Māori lives.

Conclusions

In this manuscript we have presented the most commonly diagnosed cancers for Māori, the most common causes of cancer death, and contextualised survival disparities between Māori and non-Māori against the actual mortality burden of each given cancer. If our primary objective is to reduce the overall cancer burden for Māori, then our top priority may be preventing the majority of lung cancers via tobacco eradication while simultaneously detecting lung tumours early (possibly via a targeted lung CT screening programme). Population-based initiatives aimed at the prevention of cancers related to infectious diseases, diet, obesity and diabetes will also result in a substantial reduction in the incidence and mortality cancer burden for Māori. Likewise, overall improvements in early detection and the provision of best-practice timely treatment for Māori patients will close the survival gap between Māori and non-Māori in the short- to medium-term, leading to a further reduction in Maori cancer deaths.

Appendix

Methods

Data sources

We extracted all incident cases of cancer diagnosed between 2007–2016 from the New Zealand Cancer Registry (NZCR), which we then linked to the national Mortality collection to establish those patients that had died over the study period (for the purposes of survival analysis). In addition, to determine the number of cancer deaths for each given cancer we extracted all deaths where cancer was listed as the underlying cause of death from the Mortality Collection.

Variables

Ethnicity was derived from the NZCR for cancer incidence and survival analysis, and from the Mortality collection for mortality analysis. Those with Māori ethnicity were classified as Māori, while those without Māori ethnicity were classified as non-Māori. Cancer type (eg, lung cancer) was determined using ICD codes on the NZCR. In the case of breast cancer, only female breast cancer cases were included in analysis.

Descriptive analysis

In terms of descriptive analysis, we determined the top 10 cancers that were the most commonly diagnosed among Māori over the study period on the NZCR (ie, based on absolute counts). Similarly, we determined the top 10 most common cancers that were listed as an underlying cause of death on the Mortality collection. Further incidence, mortality and survival analysis was then conducted on these cancers.

Age- and sex-standardisation

We used direct age- and sex-standardisation to calculate standardised incidence rates (SIR) and standardised mortality rates (SMR),36 using the 2001 total Māori population as the standard.37 This method aligns with that used in the reporting for the WAI2575 report.38 For incidence, numerator data were the number of cases over the study period as determined from the NZCR. For mortality, numerator data were the numbers of deaths where a given cancer was listed as the underlying cause of death on the Mortality collection. In terms of denominators, we used aggregated estimated population data from Statistics New Zealand across the study period. Age- and sex-stratified denominator data for Māori were derived from mid-year Māori estimated residential population data,39 while non-Māori denominator data were determined by subtracting the Māori denominator data from the total mid-year estimated residential population data.40 When calculating temporal trends in incidence and mortality rates, we used the estimated residential populations for each respective year as the relevant denominator (eg, 2007 Māori estimated residential population when calculating 2007 incidence rate).

Where incidence and mortality rates are presented by sex in the Appendix, the denominator and standard population used for these rates is sex-specific. For temporal analyses, we calculated a Cochran-Armitage test for trend.

Survival analysis

Cox proportional hazards models were used to describe the extent to which Māori were more or less likely to die of their cancer than non-Māori, adjusted for age (continuous variable) and sex where relevant (categorical variable). These results were described using hazard ratios (HR), with non-Māori as the reference group.

All analyses were conducted in SAS v9.4 (SAS Enterprises Inc.) and Microsoft Excel 2016 (Microsoft Corporation).

Appendix Table 1: Numbers of Māori cancer cases (incidence) and the number of cancer deaths (mortality) per year, by cancer type.

Appendix Figure 1A: Age standardised incidence rate (SIR) for the top 10 most commonly diagnosed cancers among Māori females between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori females (bottom).

Appendix Figure 1B: Age standardised incidence rate (SIR) for the top 10 most commonly diagnosed cancers among Māori males between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori females (bottom).

Appendix Figure 2A: Age- and sex-standardised mortality rate (SMR) and absolute numbers of cases for the top 10 most common causes of cancer death for Māori females between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori population (bottom).

Appendix Figure 2B: Age- and sex-standardised mortality rate (SMR) and absolute numbers of cases for the top 10 most common causes of cancer death for Māori males between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori population (bottom).

Appendix Table 2: Adjusted hazard ratios (HRs) and 95% confidence intervals, comparing the adjusted likelihood of cancer-specific death between Māori and non-Māori over the follow-up period. Total HRs are for combined sexes and are adjusted for age and sex, while sex-specific HRs are adjusted for age. HRs for cancers where fewer than 10 deaths occurred among Māori over the follow-up period are not shown.

Summary

Abstract

Cancer is an important cause of morbidity and avoidable mortality for Māori—and substantial disparities exist in cancer incidence, mortality and survival for Māori compared to non-Māori New Zealanders. In this viewpoint, we draw together cancer incidence, mortality and survival data from the previous decade, in order to provide clarity regarding the most important causes of cancer burden for Māori. Covering the decade 2007–2016, our manuscript directly leads on from the landmark Unequal Impact II report (which covered 1996–2006), and provides the most up-to-date record of this burden as is currently possible. While focusing on the absolute burden of cancer for Māori, we also compare this burden to that experienced by non-Māori, and consider how this relative disparity may (or may not) have changed over time. Finally, we discuss how to reduce the occurrence and the overall cancer mortality burden for Māori, with a focus on those cancers that confer the greatest burden.

Aim

Method

Results

Conclusion

Author Information

Jason K Gurney, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Hei Āhuru Mōwai (National Māori Cancer Leadership Group); Bridget Robson, Te Rōpū Rangahau Hauora a Eru Pōmare, Department of Public Health, University of Otago, Wellington; Jonathan Koea, Waitemata District Health Board, Auckland; Nina Scott, Hei Āhuru Mōwai (National Māori Cancer Leadership Group); Waikato District Health Board, Auckland; James Stanley, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Diana Sarfati, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Cancer Control Agency, Wellington.

Acknowledgements

We would like to thank Chris Lewis at the Ministry of Health for extracting the National Collections data presented in this manuscript. We gratefully acknowledge funding from the Health Research Council of New Zealand to support this work (HRC reference #: HRC 18/588).

Correspondence

Jason K Gurney, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, PO Box 7343, Wellington.

Correspondence Email

jason.gurney@otago.ac.nz

Competing Interests

All authors report grants from Health Research Council during the conduct of the study.

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27. Robson B, Stanley J. BreastScreen Aotearoa Programme Monitoring Report: For Maori, Pacific and Total women screened during the two or four years to June 2016: Te Rōpū Rangahau Hauora a Eru Pōmare, University of Otago Wellington, 2017.

28. Smith M, Rumlee L, Canfell K. National Cervical Screening Programme Monitoring Report, 1 January - 30 June 2017. National Screening Unit, Wellington, 2018.

29. Jackson C, Sharples K, Firth M, et al. The PIPER Project: An Internal Examination of Colorectal Cancer Management in New Zealand. Final study report to the Health Research Council and Ministry of Health., 2015.

30. Gurney J, Sarfati D, Stanley J. The impact of patient comorbidity on cancer stage at diagnosis. British Journal of Cancer 2015; 113(9):1375–80.

31. Chamberlain J, Sarfati D, Cunningham R, Koea J, Gurney J, Blakely T. Incidence and management of hepatocellular carcinoma among Māori and non-Māori New Zealanders. Australian & New Zealand Journal of Public Health 2013; 37:520–6.

32. Stevens W, Stevens G, Kolbe J, Cox B. Ethnic differences in the management of lung cancer in New Zealand. J Thorac Oncol 2008; 3(3):237–44.

33. Gurney J, Campbell S, Jackson C, Sarfati D. Equity by 2030: achieving equity in survival for Maori cancer patients. New Zealand Medical Journal 2019; 132(1505):66–76.

34. Ministry of Health. Cancer Quality Performance Indicator Programme. 2019. http://www.health.govt.nz/our-work/diseases-and-conditions/national-cancer-programme/cancer-initiatives/cancer-quality-performance-indicator-programme

35. Brewer N, Foliaki S, Bromhead C, et al. Acceptability of human papillomavirus self-sampling for cervical-cancer screening in under-screened Maori and Pasifika women: a pilot study. The New Zealand Medical Journal 2019; 132(1497):21–31.

36. Ministry of Health. Standardising rates of disease. Wellington: Ministry of Health, 1998.

37. Ministry of Health. Position paper on Māori health analytics – age standardisation. Wellington, New Zealand: Ministry of Health, 2018.

38. Tribunal W. HAUORA: Report on Stage One of the Health Services and Outcomes Kaupapa Inquiry - WAI 2575. Lower Hutt, New Zealand, 2019.

39. Statistics New Zealand. Maori Population Estimates. 2017. http://archive.stats.govt.nz/browse_for_stats/population/estimates_and_projections/MaoriPopulationEstimates_HOTPAtJun16.aspx (accessed 01/12/2019).

40. Statistics New Zealand. Estimated residential population dataset. 2019. http://archive.stats.govt.nz/infoshare (accessed 20th November 2019).

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Cancer is an important cause of morbidity and avoidable mortality for Māori, with more than a quarter of all deaths among Māori attributable to this disease.1 There is substantial evidence of enduring disparities in cancer incidence, mortality and survival between Māori and non-Māori, with cancer making an important contribution to the life expectancy gap between these groups.2

Our country’s new Cancer Action Plan for the years 2019–2029 aims to address inequities in the burden of cancer experienced by Māori New Zealanders.3 In the plan, the Ministry of Health stated that the plan would be equity-led, achieve equity by design, and included as a primary outcome that “New Zealanders experience equitable cancer outcomes”. These objectives are important and signal a commitment from central Government to closing the cancer gap for Māori.

Given the substantial inequities in cancer outcomes experienced by Māori, the prioritisation of initiatives to close this gap is congruent with the objectives of the new Plan. However, in the presence of finite capital (both fiscal and political), there is a need to carefully set priorities that reflect the reality of the cancer burden faced by Māori. While many initiatives will have pan cancer impact—such as renewed investment in the Māori cancer care workforce—there is value in understanding which cancers cause the largest burden on Māori, before we prioritise and invest in new initiatives that may increase inequities, or only impact one or two cancers (such as screening programmes).

In this manuscript, we present current evidence on the most commonly diagnosed cancers among Māori between 2007–2016, the decade immediately following on from the 1996–2006 period presented in the landmark Unequal Impact II report.2 We also present the most common causes of cancer death for Māori over this period. Alongside these absolute cancer death data, we present a relative cancer survival comparison between Māori and non-Māori. Finally, we summarise the factors that link these cancers, and discuss how to reduce their occurrence and the overall cancer mortality burden for Māori.

What are the most commonly diagnosed cancers among Māori?

Using New Zealand Cancer Registry data, we determined the 10 most commonly diagnosed cancers among Māori between 2007–2016, calculated age- and sex-standardised incidence rates (SIR), and also calculated standardised rate differences (SRD) to compare incidence between Māori and non-Māori. We determined incidence rates and rate differences for both the total population (Figure 1) and separately for males and females (Appendix Figure 1).

Figure 1: Age- and sex-standardised incidence rate (SIR) and absolute numbers of annual cases for the top 10 most commonly diagnosed cancers for Māori between 2007–2016 (top), along with the age- and sex-standardised rate difference (SRD) between Māori and Non-Māori (bottom). Analysis methods are described in the Appendix. Data is direct age- and sex-standardised to the 2001 total Māori population.

In terms of absolute numbers of cases, lung cancer was the most commonly diagnosed cancer among Māori with 401 cases/year, followed by breast (373/year), prostate (190/year) and colorectal (170 cases/year). In terms of age- and sex-standardised incidence rates, breast (SIR: 45/100,000 Māori per year) and lung (42/100,000) were highest, followed by prostate (20/100,000) and colorectal (18/100,000). The remainder of the top 10 (stomach, uterine, liver, pancreatic, and the blood cancers leukaemia and non-Hodgkin’s lymphoma) clustered around 6–10 cases/100,000 Māori. For Māori females, the most commonly diagnosed cancer was breast (88/100,000 Māori females), followed by lung (46/100,000) and colorectal cancers (17/100,000). For Māori males, the most commonly diagnosed cancer was prostate (46/100,000 Māori males), followed by lung (43/100,000) and colorectal cancers (23/100,000).

In comparison with non-Māori, Māori were more likely to be diagnosed with most of these cancers than non-Māori, particularly lung (SRD: females absolute difference of 34 cases per 100,000, males 28/100,000, total 29/100,000), but less likely to be diagnosed with colorectal (females -4/100,000, males -4/100,000, total -4/100,000) and prostate cancers (males -11/100,000).

What are the most common causes of cancer death for Māori?

Mortality

Using New Zealand Mortality Collection data, we determined the 10 most common causes of cancer death among Māori between 2007–2016, calculated age- and sex-standardised mortality rates (SMR), and also calculated standardised rate differences to compare mortality between Māori and non-Māori (SRD). Like incidence, we determined mortality rates and rate differences for both the total population (Figure 2) and separately for males and females (Appendix Figure 2).

Lung cancer was the most common cause of cancer death among Māori, with 311 deaths/year (SMR: 32/100,000). This was followed by breast (77 deaths/year, 9/100,000 Māori) and colorectal cancers (68 deaths/year, 7/100,000). The remainder of the top 10 (stomach, liver, pancreatic, ill-defined, prostate, leukaemia and non-Hodgkin’s lymphoma) caused between 20–50 deaths per year (2–6/100,000). The most common cause of cancer death among Māori females was lung (34/100,000 females), followed by breast (17/100,000) and colorectal cancers (6/100,000). The most common cause of cancer death among Māori males was lung (34/100,000 Māori males), followed by colorectal (10/100,000) and prostate cancers (9/100,000).

In comparison with non-Māori, Māori were more likely to die from most of these cancers than non-Māori, particularly lung (SRD: absolute difference in rates for females 25/100,000, males 22/100,000, total 23/100,000), although differences for colorectal cancer were negligible (females -2/100,000, males 0/100,000, total -1/100,000).

There is obvious crossover between the incidence and mortality figures presented above, with nine of the top 10 cancers occurring on both lists. Cancer mortality is of course intrinsically linked to cancer incidence: the more common a cancer is, the more common that death from that cancer will be. As such, many cancer deaths are avoidable via prevention of cancer incidence; but many cancer deaths are also avoidable via improvements in the likelihood of survival following a cancer diagnosis. Like incidence, cancer survival is a factor which is not equal between Māori and non-Māori.2

Survival

In Figure 3, we have plotted the absolute number of cancer deaths among Māori per year (y-axis) against the relative disparity in cancer survival (ie, post-diagnosis survival) between Māori and non-Māori (x-axis). This figure helps us to contextualise relative disparities in cancer survival against the actual absolute mortality burden experienced by Māori. For example, the strongest observed survival disparity is found for melanoma (age-sex-adjusted hazard ratio [HR]: 2.6, 95% CI 2.0–3.3), but fewer than six Māori died of this cancer per year over the study period (5.9 deaths/year). Contrast this with lung cancer, for which the survival disparity is smaller (HR: 1.3, 95% CI 1.2–1.4) but the mortality burden is much higher (311 Māori deaths/year). Importantly, survival is poorer for Māori compared to non-Māori for each of the top 10 causes of Māori cancer death, with adjusted hazard ratios ranging from 1.1 (pancreatic cancer) to 2.1 (prostate cancer). A complete list of hazard ratios for all cancers, for both the total combined population and stratified by sex, are presented in Appendix Table 2.

Figure 3: Scatterplot showing the average annual cancer-specific deaths among Māori (2007–2016) versus cancer-specific mortality hazard ratios (Māori vs Non-Māori), for a) all cancers including lung cancer; and b) all cancers excluding lung cancer. Only cancers where at least five cancer deaths occurred per year are plotted. Analysis methods are described in the Appendix. HRs are presented on the logarithmic scale.

What is happening over time?

Investigating temporal trends in incidence, mortality and survival can help us to understand whether (or not) we are making progress in achieving better cancer outcomes for Māori. In Figure 4, we present the age-sex-standardised incidence, mortality and rate differences for each year between 2007–2016. We have focused on lung cancer as both the most commonly diagnosed and most common cause of cancer death for Māori men and women.

Figure 4: Lung cancer age-sex-standardised incidence rate and rate difference (top), mortality rate and rate difference (middle), and differences in survival between Māori and non-Māori (bottom) over the 2007–2016 period. For the survival analysis, shaded areas indicate 95% confidence intervals. (Note: the observed abrupt increase in recorded lung cancer deaths in 2015 is unexplained, and we are investigating this with National Collections.)

From Figure 4 we observe that, for the most common cause of cancer and cancer death for Māori (lung cancer), both incidence and mortality appear to be reducing over time—along with the disparities between Māori and non-Māori for these measures. However, disparities in lung cancer survival for Māori compared to non-Māori have remained relatively unchanged over the previous decade, ranging between 20–40% excess mortality with no clear temporal trend in either direction (Figure 4).

How do we reduce the cancer burden for Māori?

The factors underpinning overall worse cancer incidence, mortality and survival for Māori are systemic. These outcomes are driven by inequities in the social determinants of good health, determinants that are structural in nature and not controlled by Māori (just as they are not controlled by other indigenous and minority populations around the world).4 In the context of cancer, these determinants combine to increase Māori exposure to carcinogens, to prevent access to screening and early detection, and to prevent timely access to best-practice curative treatment. These factors occur across cancers, and the extent to which they impact on outcomes will depend on the unique characteristics of each cancer.

A systems-level problem requires system-level solutions. Broad health system actions that impact multiple cancers—such as improving access for Māori to timely diagnosis and appropriate treatment, regardless of income or place of residence—are crucial. Likewise, enhancing Māori access to cancer control decision-making, coupled with the resources required to improve cancer prevention, early detection, treatment and support for Māori-led approaches to providing these services, are also vital. While these broad actions are necessary, dismantling the barriers to equitable cancer outcomes for Māori will require a cancer-specific approach in some instances. In an absolute sense, the cancers identified in Figures 1 and 2 have the most profound impact on overall cancer mortality for Māori. However, systemic actions to reduce Māori cancer deaths should not necessarily be prioritised towards cancers in order of burden. To be effective, such prioritisation must take into account factors such as preventability of the cancer, ability to detect the cancer at an early stage, prognosis of the cancer once it is detected, and the availability of curative treatment options within a given cancer context.

Prevention

More than half of the top 10 most common cancers among Māori (Figure 1) and the top 10 most common causes of cancer death for Māori (Figure 2) have known key aetiological exposures that disproportionately impact Māori compared to non-Māori. These exposures can be broadly grouped as tobacco exposure (lung5 and pancreatic6 cancers), infectious diseases (stomach7 and liver8 cancers9), diet and obesity/diabetes mellitus (breast,10 uterine,10 colorectal10 and pancreatic6 cancers) and familial genetic predisposition (stomach cancer11). Māori are substantially more likely to be exposed to tobacco,12 to be exposed to infection with Helicobacter pylori7 and the Hepatitis virus,13 and to be exposed to the structural causes of obesity and diabetes.14

The relative contribution of each of these known exposures to the incidence of a given cancer varies depending on the context. The attributable fraction of lung cancer cases caused by tobacco exposure has been estimated to be between 80–90%.15,16 More than a third of uterine cancers are attributable to obesity.10 More than two-thirds of all stomach cancers are attributable to Helicobacter pylori infection, with this bacterium responsible for 90% of non-cardia stomach cancers—the most common form of stomach cancer diagnosed among Māori.17 Nearly 40% of all liver cancers worldwide are attributable to the hepatitis B or C virus,9 and 70% of Māori liver cancer patients will have a history of hepatitis B or C infection, suggesting a much higher attributable fraction for Māori than the international average.18 In Australia and New Zealand an estimated 17% of pancreatic cancer cases are attributable to high fasting plasma glucose (consistent with pre- or established diabetes mellitus), around the same as that attributable to tobacco exposure.6

Thus, a substantial proportion of the most common causes of cancer and cancer death for Māori are attributable to known preventable exposures. We can draw hope and encouragement from the knowledge that the means of preventing a substantial proportion of cancers for Māori are within our grasp—and include steadfast commitment to Smokefree 2025 (with a stronger focus on smoking in Māori), exploration of Helicobacter pylori test-and-treat programmes, revived vigour in (and monitoring of) our hepatitis vaccination and surveillance programmes, and a regulatory commitment to ensuring that nutritious and healthy lifestyles are accessible and affordable for all (particularly Māori). This hope must be accompanied with renewed determination and innovation to make these tools work for Māori. National cancer prevention policies should combine a population-based and underserved population approach—known as proportionate universalism19—and emphasis on the factors outlined here is consistent with this approach. Perhaps most crucially, an approach that focuses resources on the prevention of cancers that have the strongest impact on Māori is consistent with the principles of the Treaty of Waitangi, which require the Crown to take active measures to restore balance in situations where Māori have been disadvantaged.20

Reducing Māori cancer deaths

Five of the top 10 causes of cancer death for Māori (lung, stomach, pancreas, liver, ill-defined) have an expected one-year survival of less than 50%, with the most common cause (lung) having a one-year survival of approximately 35% for both Māori and non-Māori (data not shown). The nature of tumour development within these cancer types means that disease detection often does not occur until tumours have metastasised, at which point the benefit of a curative therapeutic approach is questionable. More than two-thirds of all Māori cancer deaths each year occur among these poor-prognosis cancers (Figure 2).

With this in mind, the primary key to reducing cancer deaths for Māori is by preventing the cancer in the first place (see above). If prevention is unsuccessful, then the next highest priority is early detection, when curative treatment is still possible. Once the cancer is diagnosed, the highest priority becomes ensuring access to timely best-practice treatment for the given tumour type and sub-type. Unfortunately, there is evidence that Māori are underserved in each of these post-diagnosis priorities.21,22 There are some burgeoning examples of high Māori screening participation in some regions (eg, the Southern DHB bowel screening programme), and these successes should be examined, documented and modeled where appropriate.

Early detection and screening

Early detection of primary lung cancer currently relies on either presentation of a patient with respiratory symptoms, or on chance findings following examination for other conditions (eg, chest x-ray for suspected heart disease). Given the poor prognosis of lung cancer, detection of tumours at the asymptomatic stage may increase the chances of survival via curative treatment. Studies investigating the efficacy of lung cancer screening via computed tomography (CT) scan have been promising.23–25 Preparatory lung cancer screening work is currently being completed in various locations throughout New Zealand, with the results of this preparatory work of critical importance to Māori health. National screening programmes for breast and colorectal cancers—both in the top three most common causes of cancer death for Māori—are in operation, although the latter programme is in its infancy and as of January 2020 was operational in 10 of the 20 district health boards.26 With evidence that Māori have poorer access to national screening programmes than non-Māori,27,28 there is an urgent need for renewed prioritisation and vigour in maximising Māori participation across these programmes.

Many of the most commonly diagnosed cancers among Māori are diagnosed outside of screening programmes. Diagnosis of these cancers principally relies on detection through primary care, although there is evidence that Māori are more likely to be diagnosed following acute admission at an emergency department.29 Maximising early diagnosis of cancers for Māori requires us to consider the key barriers to early diagnosis that Māori (to a greater extent than non-Māori) face. These include the financial burden of general practitioner visits, transport and travel, as well as other factors including patient comorbidity that may complicate diagnosis.30 In essence, we need to recognise that our current means of early detection systemically disadvantages Māori, and that this disadvantage contributes to the perpetuation of inequities in cancer death between Māori and non-Māori.

In terms of specific actions that impact on the cancers in Figures 1 and 2, the pathways for achieving important health gain for Māori will vary depending on the cancer. For example, an important pathway in terms of early detection of liver cancer for Māori is hepatitis surveillance. As noted above, hepatitis B and C appear to be the primary causes of liver cancer for Māori; however, Māori are underserved by the current national hepatitis surveillance programme. We previously observed that, in a cohort of Māori liver cancer patients with hepatitis B or C, only around 40% were on surveillance.31 Crucially, more than three-quarters (77%) of those not on surveillance were diagnosed with stage III or later disease, compared to 33% of those who were on surveillance.31 These observations, echoes of which can be observed across cancers, strongly suggest that careful scrutiny of the barriers to hepatitis surveillance could yield important health gains for Māori with liver disease.

Access to best-practice and timely treatment

There is compelling evidence that Māori have poorer access to timely best-practice treatment compared to non-Māori.21 For example, Stevens et al32 observed that Māori lung cancer patients were 60% less likely to be referred to a medical oncologist than non-Māori and were 70% less likely to receive curative treatment. Because we know that Māori have generally poorer access to best-practice and timely care, cancer care services have an important role to play in reducing the cancer burden for Māori.

In their global report on the drivers of social inequalities in cancer outcomes, the International Agency for Research on Cancer (IARC)4 summarised the key drivers of equitable access to cancer care as the following three A’s:

Availability: The physical availability of high-quality cancer care services, how well resourced and managed these services are, and how well they communicate with patients.

Affordability: The financial accessibility of the cancer treatment journey, from the costs of care to travel/transportation and loss of income.

Acceptability: How cancer care services are perceived by population groups, in terms of factors including effectiveness of care (ie, whether the care will actually work) and cultural competency of the system (ie, how similar/dissimilar the system is to your own culture).4

We can identify our own system within these three A’s, and how these are likely to be contributing to poorer cancer outcomes for Māori. Relevant factors include where services are located relative to where Māori live, the reality that some best-practice treatments are only available if privately funded, the inflexible nature of pathways of cancer care that do not necessarily reflect the priorities of Māori, and inadequate resourcing of Māori treatment providers and navigators.33 Each of these factors (and others) are important sources of disparities in access to care and poor cancer outcomes for Māori, and will be occurring to a different extent across cancer types. Underpinning the receipt of best-practice and timely care by Māori is the existence of standards of care (such as those recently published for colorectal cancer34) that clearly benchmark what a patient should expect to receive during their cancer care, and an unerring apolitical commitment to ensuring these standards are met for Māori across all district health boards in New Zealand.

Other opportunities for improvements in cancer outcomes for Māori

While we have focused in this manuscript on the cancers that present the greatest overall cancer burden on Māori, this does not detract from the importance of cancers that may be less common but will have equal impact at an individual (and whānau) level. For example, while the number of Māori female deaths from cervical cancer (11/year; Appendix Table 1) is far fewer than lung or breast cancers, the large survival disparity between Māori and non-Māori (adjusted HR: 1.4, 95% CI 1.1–1.8) suggests that there is room within existing systems for substantial improvement that will save the lives of Māori women. The advent self-testing kits for human Papilloma virus (HPV, the cause of all cases of cervical cancer9) will likely increase the uptake of cervical screening among those who did not previously access this screening.35 This is important, and might address the current substantial disparity in access to the national cervical screening programme among screen-age Māori women (64%) compared to European women (81%).28 Resourcing of cancer control initiatives aimed at reducing the cancer burden for Māori must take into account the burden of a given cancer, as outlined throughout this manuscript—but they must also remain flexible to ensure that we do not miss opportunities for relatively straightforward interventions (such as HPV self-testing) that will invariably save Māori lives.

Conclusions

In this manuscript we have presented the most commonly diagnosed cancers for Māori, the most common causes of cancer death, and contextualised survival disparities between Māori and non-Māori against the actual mortality burden of each given cancer. If our primary objective is to reduce the overall cancer burden for Māori, then our top priority may be preventing the majority of lung cancers via tobacco eradication while simultaneously detecting lung tumours early (possibly via a targeted lung CT screening programme). Population-based initiatives aimed at the prevention of cancers related to infectious diseases, diet, obesity and diabetes will also result in a substantial reduction in the incidence and mortality cancer burden for Māori. Likewise, overall improvements in early detection and the provision of best-practice timely treatment for Māori patients will close the survival gap between Māori and non-Māori in the short- to medium-term, leading to a further reduction in Maori cancer deaths.

Appendix

Methods

Data sources

We extracted all incident cases of cancer diagnosed between 2007–2016 from the New Zealand Cancer Registry (NZCR), which we then linked to the national Mortality collection to establish those patients that had died over the study period (for the purposes of survival analysis). In addition, to determine the number of cancer deaths for each given cancer we extracted all deaths where cancer was listed as the underlying cause of death from the Mortality Collection.

Variables

Ethnicity was derived from the NZCR for cancer incidence and survival analysis, and from the Mortality collection for mortality analysis. Those with Māori ethnicity were classified as Māori, while those without Māori ethnicity were classified as non-Māori. Cancer type (eg, lung cancer) was determined using ICD codes on the NZCR. In the case of breast cancer, only female breast cancer cases were included in analysis.

Descriptive analysis

In terms of descriptive analysis, we determined the top 10 cancers that were the most commonly diagnosed among Māori over the study period on the NZCR (ie, based on absolute counts). Similarly, we determined the top 10 most common cancers that were listed as an underlying cause of death on the Mortality collection. Further incidence, mortality and survival analysis was then conducted on these cancers.

Age- and sex-standardisation

We used direct age- and sex-standardisation to calculate standardised incidence rates (SIR) and standardised mortality rates (SMR),36 using the 2001 total Māori population as the standard.37 This method aligns with that used in the reporting for the WAI2575 report.38 For incidence, numerator data were the number of cases over the study period as determined from the NZCR. For mortality, numerator data were the numbers of deaths where a given cancer was listed as the underlying cause of death on the Mortality collection. In terms of denominators, we used aggregated estimated population data from Statistics New Zealand across the study period. Age- and sex-stratified denominator data for Māori were derived from mid-year Māori estimated residential population data,39 while non-Māori denominator data were determined by subtracting the Māori denominator data from the total mid-year estimated residential population data.40 When calculating temporal trends in incidence and mortality rates, we used the estimated residential populations for each respective year as the relevant denominator (eg, 2007 Māori estimated residential population when calculating 2007 incidence rate).

Where incidence and mortality rates are presented by sex in the Appendix, the denominator and standard population used for these rates is sex-specific. For temporal analyses, we calculated a Cochran-Armitage test for trend.

Survival analysis

Cox proportional hazards models were used to describe the extent to which Māori were more or less likely to die of their cancer than non-Māori, adjusted for age (continuous variable) and sex where relevant (categorical variable). These results were described using hazard ratios (HR), with non-Māori as the reference group.

All analyses were conducted in SAS v9.4 (SAS Enterprises Inc.) and Microsoft Excel 2016 (Microsoft Corporation).

Appendix Table 1: Numbers of Māori cancer cases (incidence) and the number of cancer deaths (mortality) per year, by cancer type.

Appendix Figure 1A: Age standardised incidence rate (SIR) for the top 10 most commonly diagnosed cancers among Māori females between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori females (bottom).

Appendix Figure 1B: Age standardised incidence rate (SIR) for the top 10 most commonly diagnosed cancers among Māori males between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori females (bottom).

Appendix Figure 2A: Age- and sex-standardised mortality rate (SMR) and absolute numbers of cases for the top 10 most common causes of cancer death for Māori females between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori population (bottom).

Appendix Figure 2B: Age- and sex-standardised mortality rate (SMR) and absolute numbers of cases for the top 10 most common causes of cancer death for Māori males between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori population (bottom).

Appendix Table 2: Adjusted hazard ratios (HRs) and 95% confidence intervals, comparing the adjusted likelihood of cancer-specific death between Māori and non-Māori over the follow-up period. Total HRs are for combined sexes and are adjusted for age and sex, while sex-specific HRs are adjusted for age. HRs for cancers where fewer than 10 deaths occurred among Māori over the follow-up period are not shown.

Summary

Abstract

Cancer is an important cause of morbidity and avoidable mortality for Māori—and substantial disparities exist in cancer incidence, mortality and survival for Māori compared to non-Māori New Zealanders. In this viewpoint, we draw together cancer incidence, mortality and survival data from the previous decade, in order to provide clarity regarding the most important causes of cancer burden for Māori. Covering the decade 2007–2016, our manuscript directly leads on from the landmark Unequal Impact II report (which covered 1996–2006), and provides the most up-to-date record of this burden as is currently possible. While focusing on the absolute burden of cancer for Māori, we also compare this burden to that experienced by non-Māori, and consider how this relative disparity may (or may not) have changed over time. Finally, we discuss how to reduce the occurrence and the overall cancer mortality burden for Māori, with a focus on those cancers that confer the greatest burden.

Aim

Method

Results

Conclusion

Author Information

Jason K Gurney, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Hei Āhuru Mōwai (National Māori Cancer Leadership Group); Bridget Robson, Te Rōpū Rangahau Hauora a Eru Pōmare, Department of Public Health, University of Otago, Wellington; Jonathan Koea, Waitemata District Health Board, Auckland; Nina Scott, Hei Āhuru Mōwai (National Māori Cancer Leadership Group); Waikato District Health Board, Auckland; James Stanley, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Diana Sarfati, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Cancer Control Agency, Wellington.

Acknowledgements

We would like to thank Chris Lewis at the Ministry of Health for extracting the National Collections data presented in this manuscript. We gratefully acknowledge funding from the Health Research Council of New Zealand to support this work (HRC reference #: HRC 18/588).

Correspondence

Jason K Gurney, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, PO Box 7343, Wellington.

Correspondence Email

jason.gurney@otago.ac.nz

Competing Interests

All authors report grants from Health Research Council during the conduct of the study.

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13. Blakely T, Salmond C, Tobias M. Hepatitis B virus carrier prevalence in New Zealand: population estimates using the 1987 police and customs personnel survey. The New Zealand Medical Journal 1998; 111(1064):142–4.

14. Theodore R, McLean R, TeMorenga L. Challenges to addressing obesity for Māori in Aotearoa/New Zealand. Australian and New Zealand journal of public health 2015; 39(6):509–12.

15. Parkin DM. 2. Tobacco-attributable cancer burden in the UK in 2010. Br J Cancer 2011; 105 Suppl 2: S6–s13.

16. International Agency for Research on Cancer. Attributable causes of cancer in France in the year 2000. Lyon, France: International Agency for Research on Cancer, 2007.

17. Signal V, Sarfati D, Cunningham R, Gurney J, Koea J, Ellison-Loschmann L. Indigenous inequities in the presentation and management of stomach cancer in New Zealand: a country with universal health care coverage. Gastric Cancer 2015; 18(3):571–9.

18. Blakely TA, Bates MN, Baker MG, Tobias M. Hepatitis B carriage explains the excess rate of hepatocellular carcinoma for Maori, Pacific Island and Asian people compared to Europeans in New Zealand. Int J Epidemiol 1999; 28(2):204–10.

19. Menvielle G, Kulhánová I, Mackenbach JP. Chapter 14. Assessing the impact of a public health intervention to reduce social inequalities in cancer. In: Vaccarella S, Lortet-Tieulent J, Saracci R, Conway DI, Straif K, Wild CP, eds. Reducing social inequalities in cancer: evidence and priorities for research: IARC Scientific Publications; 2019:304–18.

20. Reid P, Paine SJ, Curtis E, et al. Achieving health equity in Aotearoa: Strengthening responsiveness to Maori in health research. New Zealand Medical Journal 2017; 130(1465):96–103.

21. Hill S, Sarfati D, Robson B, Blakely T. Indigenous inequalities in cancer: What role for health care? ANZ journal of surgery 2013; 83(1–2):36–41.

22. Gurney J, Stanley J, Jackson C, Sarfati D. Stage at diagnosis for Maori cancer patients: disparities, similarities and data limitations. New Zealand Medical Journal 2020; In Press.

23. Usman Ali M, Miller J, Peirson L, et al. Screening for lung cancer: A systematic review and meta-analysis. Preventive medicine 2016; 89:301–14.

24. Rota M, Pizzato M, La Vecchia C, Boffetta P. Efficacy of lung cancer screening appears to increase with prolonged intervention: results from the MILD trial and a meta-analysis. Annals of Oncology 2019; 30(7):1040–3.

25. Oudkerk M, Devaraj A, Vliegenthart R, et al. European position statement on lung cancer screening. The Lancet Oncology 2017; 18(12):e754–e66.

26. Ministry of Health. About the National Bowel Screening Programme. 2019. http://www.timetoscreen.nz/bowel-screening/about-the-national-bowel-screening-programme/ (accessed 14/01/2020.

27. Robson B, Stanley J. BreastScreen Aotearoa Programme Monitoring Report: For Maori, Pacific and Total women screened during the two or four years to June 2016: Te Rōpū Rangahau Hauora a Eru Pōmare, University of Otago Wellington, 2017.

28. Smith M, Rumlee L, Canfell K. National Cervical Screening Programme Monitoring Report, 1 January - 30 June 2017. National Screening Unit, Wellington, 2018.

29. Jackson C, Sharples K, Firth M, et al. The PIPER Project: An Internal Examination of Colorectal Cancer Management in New Zealand. Final study report to the Health Research Council and Ministry of Health., 2015.

30. Gurney J, Sarfati D, Stanley J. The impact of patient comorbidity on cancer stage at diagnosis. British Journal of Cancer 2015; 113(9):1375–80.

31. Chamberlain J, Sarfati D, Cunningham R, Koea J, Gurney J, Blakely T. Incidence and management of hepatocellular carcinoma among Māori and non-Māori New Zealanders. Australian & New Zealand Journal of Public Health 2013; 37:520–6.

32. Stevens W, Stevens G, Kolbe J, Cox B. Ethnic differences in the management of lung cancer in New Zealand. J Thorac Oncol 2008; 3(3):237–44.

33. Gurney J, Campbell S, Jackson C, Sarfati D. Equity by 2030: achieving equity in survival for Maori cancer patients. New Zealand Medical Journal 2019; 132(1505):66–76.

34. Ministry of Health. Cancer Quality Performance Indicator Programme. 2019. http://www.health.govt.nz/our-work/diseases-and-conditions/national-cancer-programme/cancer-initiatives/cancer-quality-performance-indicator-programme

35. Brewer N, Foliaki S, Bromhead C, et al. Acceptability of human papillomavirus self-sampling for cervical-cancer screening in under-screened Maori and Pasifika women: a pilot study. The New Zealand Medical Journal 2019; 132(1497):21–31.

36. Ministry of Health. Standardising rates of disease. Wellington: Ministry of Health, 1998.

37. Ministry of Health. Position paper on Māori health analytics – age standardisation. Wellington, New Zealand: Ministry of Health, 2018.

38. Tribunal W. HAUORA: Report on Stage One of the Health Services and Outcomes Kaupapa Inquiry - WAI 2575. Lower Hutt, New Zealand, 2019.

39. Statistics New Zealand. Maori Population Estimates. 2017. http://archive.stats.govt.nz/browse_for_stats/population/estimates_and_projections/MaoriPopulationEstimates_HOTPAtJun16.aspx (accessed 01/12/2019).

40. Statistics New Zealand. Estimated residential population dataset. 2019. http://archive.stats.govt.nz/infoshare (accessed 20th November 2019).

Contact diana@nzma.org.nz
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Cancer is an important cause of morbidity and avoidable mortality for Māori, with more than a quarter of all deaths among Māori attributable to this disease.1 There is substantial evidence of enduring disparities in cancer incidence, mortality and survival between Māori and non-Māori, with cancer making an important contribution to the life expectancy gap between these groups.2

Our country’s new Cancer Action Plan for the years 2019–2029 aims to address inequities in the burden of cancer experienced by Māori New Zealanders.3 In the plan, the Ministry of Health stated that the plan would be equity-led, achieve equity by design, and included as a primary outcome that “New Zealanders experience equitable cancer outcomes”. These objectives are important and signal a commitment from central Government to closing the cancer gap for Māori.

Given the substantial inequities in cancer outcomes experienced by Māori, the prioritisation of initiatives to close this gap is congruent with the objectives of the new Plan. However, in the presence of finite capital (both fiscal and political), there is a need to carefully set priorities that reflect the reality of the cancer burden faced by Māori. While many initiatives will have pan cancer impact—such as renewed investment in the Māori cancer care workforce—there is value in understanding which cancers cause the largest burden on Māori, before we prioritise and invest in new initiatives that may increase inequities, or only impact one or two cancers (such as screening programmes).

In this manuscript, we present current evidence on the most commonly diagnosed cancers among Māori between 2007–2016, the decade immediately following on from the 1996–2006 period presented in the landmark Unequal Impact II report.2 We also present the most common causes of cancer death for Māori over this period. Alongside these absolute cancer death data, we present a relative cancer survival comparison between Māori and non-Māori. Finally, we summarise the factors that link these cancers, and discuss how to reduce their occurrence and the overall cancer mortality burden for Māori.

What are the most commonly diagnosed cancers among Māori?

Using New Zealand Cancer Registry data, we determined the 10 most commonly diagnosed cancers among Māori between 2007–2016, calculated age- and sex-standardised incidence rates (SIR), and also calculated standardised rate differences (SRD) to compare incidence between Māori and non-Māori. We determined incidence rates and rate differences for both the total population (Figure 1) and separately for males and females (Appendix Figure 1).

Figure 1: Age- and sex-standardised incidence rate (SIR) and absolute numbers of annual cases for the top 10 most commonly diagnosed cancers for Māori between 2007–2016 (top), along with the age- and sex-standardised rate difference (SRD) between Māori and Non-Māori (bottom). Analysis methods are described in the Appendix. Data is direct age- and sex-standardised to the 2001 total Māori population.

In terms of absolute numbers of cases, lung cancer was the most commonly diagnosed cancer among Māori with 401 cases/year, followed by breast (373/year), prostate (190/year) and colorectal (170 cases/year). In terms of age- and sex-standardised incidence rates, breast (SIR: 45/100,000 Māori per year) and lung (42/100,000) were highest, followed by prostate (20/100,000) and colorectal (18/100,000). The remainder of the top 10 (stomach, uterine, liver, pancreatic, and the blood cancers leukaemia and non-Hodgkin’s lymphoma) clustered around 6–10 cases/100,000 Māori. For Māori females, the most commonly diagnosed cancer was breast (88/100,000 Māori females), followed by lung (46/100,000) and colorectal cancers (17/100,000). For Māori males, the most commonly diagnosed cancer was prostate (46/100,000 Māori males), followed by lung (43/100,000) and colorectal cancers (23/100,000).

In comparison with non-Māori, Māori were more likely to be diagnosed with most of these cancers than non-Māori, particularly lung (SRD: females absolute difference of 34 cases per 100,000, males 28/100,000, total 29/100,000), but less likely to be diagnosed with colorectal (females -4/100,000, males -4/100,000, total -4/100,000) and prostate cancers (males -11/100,000).

What are the most common causes of cancer death for Māori?

Mortality

Using New Zealand Mortality Collection data, we determined the 10 most common causes of cancer death among Māori between 2007–2016, calculated age- and sex-standardised mortality rates (SMR), and also calculated standardised rate differences to compare mortality between Māori and non-Māori (SRD). Like incidence, we determined mortality rates and rate differences for both the total population (Figure 2) and separately for males and females (Appendix Figure 2).

Lung cancer was the most common cause of cancer death among Māori, with 311 deaths/year (SMR: 32/100,000). This was followed by breast (77 deaths/year, 9/100,000 Māori) and colorectal cancers (68 deaths/year, 7/100,000). The remainder of the top 10 (stomach, liver, pancreatic, ill-defined, prostate, leukaemia and non-Hodgkin’s lymphoma) caused between 20–50 deaths per year (2–6/100,000). The most common cause of cancer death among Māori females was lung (34/100,000 females), followed by breast (17/100,000) and colorectal cancers (6/100,000). The most common cause of cancer death among Māori males was lung (34/100,000 Māori males), followed by colorectal (10/100,000) and prostate cancers (9/100,000).

In comparison with non-Māori, Māori were more likely to die from most of these cancers than non-Māori, particularly lung (SRD: absolute difference in rates for females 25/100,000, males 22/100,000, total 23/100,000), although differences for colorectal cancer were negligible (females -2/100,000, males 0/100,000, total -1/100,000).

There is obvious crossover between the incidence and mortality figures presented above, with nine of the top 10 cancers occurring on both lists. Cancer mortality is of course intrinsically linked to cancer incidence: the more common a cancer is, the more common that death from that cancer will be. As such, many cancer deaths are avoidable via prevention of cancer incidence; but many cancer deaths are also avoidable via improvements in the likelihood of survival following a cancer diagnosis. Like incidence, cancer survival is a factor which is not equal between Māori and non-Māori.2

Survival

In Figure 3, we have plotted the absolute number of cancer deaths among Māori per year (y-axis) against the relative disparity in cancer survival (ie, post-diagnosis survival) between Māori and non-Māori (x-axis). This figure helps us to contextualise relative disparities in cancer survival against the actual absolute mortality burden experienced by Māori. For example, the strongest observed survival disparity is found for melanoma (age-sex-adjusted hazard ratio [HR]: 2.6, 95% CI 2.0–3.3), but fewer than six Māori died of this cancer per year over the study period (5.9 deaths/year). Contrast this with lung cancer, for which the survival disparity is smaller (HR: 1.3, 95% CI 1.2–1.4) but the mortality burden is much higher (311 Māori deaths/year). Importantly, survival is poorer for Māori compared to non-Māori for each of the top 10 causes of Māori cancer death, with adjusted hazard ratios ranging from 1.1 (pancreatic cancer) to 2.1 (prostate cancer). A complete list of hazard ratios for all cancers, for both the total combined population and stratified by sex, are presented in Appendix Table 2.

Figure 3: Scatterplot showing the average annual cancer-specific deaths among Māori (2007–2016) versus cancer-specific mortality hazard ratios (Māori vs Non-Māori), for a) all cancers including lung cancer; and b) all cancers excluding lung cancer. Only cancers where at least five cancer deaths occurred per year are plotted. Analysis methods are described in the Appendix. HRs are presented on the logarithmic scale.

What is happening over time?

Investigating temporal trends in incidence, mortality and survival can help us to understand whether (or not) we are making progress in achieving better cancer outcomes for Māori. In Figure 4, we present the age-sex-standardised incidence, mortality and rate differences for each year between 2007–2016. We have focused on lung cancer as both the most commonly diagnosed and most common cause of cancer death for Māori men and women.

Figure 4: Lung cancer age-sex-standardised incidence rate and rate difference (top), mortality rate and rate difference (middle), and differences in survival between Māori and non-Māori (bottom) over the 2007–2016 period. For the survival analysis, shaded areas indicate 95% confidence intervals. (Note: the observed abrupt increase in recorded lung cancer deaths in 2015 is unexplained, and we are investigating this with National Collections.)

From Figure 4 we observe that, for the most common cause of cancer and cancer death for Māori (lung cancer), both incidence and mortality appear to be reducing over time—along with the disparities between Māori and non-Māori for these measures. However, disparities in lung cancer survival for Māori compared to non-Māori have remained relatively unchanged over the previous decade, ranging between 20–40% excess mortality with no clear temporal trend in either direction (Figure 4).

How do we reduce the cancer burden for Māori?

The factors underpinning overall worse cancer incidence, mortality and survival for Māori are systemic. These outcomes are driven by inequities in the social determinants of good health, determinants that are structural in nature and not controlled by Māori (just as they are not controlled by other indigenous and minority populations around the world).4 In the context of cancer, these determinants combine to increase Māori exposure to carcinogens, to prevent access to screening and early detection, and to prevent timely access to best-practice curative treatment. These factors occur across cancers, and the extent to which they impact on outcomes will depend on the unique characteristics of each cancer.

A systems-level problem requires system-level solutions. Broad health system actions that impact multiple cancers—such as improving access for Māori to timely diagnosis and appropriate treatment, regardless of income or place of residence—are crucial. Likewise, enhancing Māori access to cancer control decision-making, coupled with the resources required to improve cancer prevention, early detection, treatment and support for Māori-led approaches to providing these services, are also vital. While these broad actions are necessary, dismantling the barriers to equitable cancer outcomes for Māori will require a cancer-specific approach in some instances. In an absolute sense, the cancers identified in Figures 1 and 2 have the most profound impact on overall cancer mortality for Māori. However, systemic actions to reduce Māori cancer deaths should not necessarily be prioritised towards cancers in order of burden. To be effective, such prioritisation must take into account factors such as preventability of the cancer, ability to detect the cancer at an early stage, prognosis of the cancer once it is detected, and the availability of curative treatment options within a given cancer context.

Prevention

More than half of the top 10 most common cancers among Māori (Figure 1) and the top 10 most common causes of cancer death for Māori (Figure 2) have known key aetiological exposures that disproportionately impact Māori compared to non-Māori. These exposures can be broadly grouped as tobacco exposure (lung5 and pancreatic6 cancers), infectious diseases (stomach7 and liver8 cancers9), diet and obesity/diabetes mellitus (breast,10 uterine,10 colorectal10 and pancreatic6 cancers) and familial genetic predisposition (stomach cancer11). Māori are substantially more likely to be exposed to tobacco,12 to be exposed to infection with Helicobacter pylori7 and the Hepatitis virus,13 and to be exposed to the structural causes of obesity and diabetes.14

The relative contribution of each of these known exposures to the incidence of a given cancer varies depending on the context. The attributable fraction of lung cancer cases caused by tobacco exposure has been estimated to be between 80–90%.15,16 More than a third of uterine cancers are attributable to obesity.10 More than two-thirds of all stomach cancers are attributable to Helicobacter pylori infection, with this bacterium responsible for 90% of non-cardia stomach cancers—the most common form of stomach cancer diagnosed among Māori.17 Nearly 40% of all liver cancers worldwide are attributable to the hepatitis B or C virus,9 and 70% of Māori liver cancer patients will have a history of hepatitis B or C infection, suggesting a much higher attributable fraction for Māori than the international average.18 In Australia and New Zealand an estimated 17% of pancreatic cancer cases are attributable to high fasting plasma glucose (consistent with pre- or established diabetes mellitus), around the same as that attributable to tobacco exposure.6

Thus, a substantial proportion of the most common causes of cancer and cancer death for Māori are attributable to known preventable exposures. We can draw hope and encouragement from the knowledge that the means of preventing a substantial proportion of cancers for Māori are within our grasp—and include steadfast commitment to Smokefree 2025 (with a stronger focus on smoking in Māori), exploration of Helicobacter pylori test-and-treat programmes, revived vigour in (and monitoring of) our hepatitis vaccination and surveillance programmes, and a regulatory commitment to ensuring that nutritious and healthy lifestyles are accessible and affordable for all (particularly Māori). This hope must be accompanied with renewed determination and innovation to make these tools work for Māori. National cancer prevention policies should combine a population-based and underserved population approach—known as proportionate universalism19—and emphasis on the factors outlined here is consistent with this approach. Perhaps most crucially, an approach that focuses resources on the prevention of cancers that have the strongest impact on Māori is consistent with the principles of the Treaty of Waitangi, which require the Crown to take active measures to restore balance in situations where Māori have been disadvantaged.20

Reducing Māori cancer deaths

Five of the top 10 causes of cancer death for Māori (lung, stomach, pancreas, liver, ill-defined) have an expected one-year survival of less than 50%, with the most common cause (lung) having a one-year survival of approximately 35% for both Māori and non-Māori (data not shown). The nature of tumour development within these cancer types means that disease detection often does not occur until tumours have metastasised, at which point the benefit of a curative therapeutic approach is questionable. More than two-thirds of all Māori cancer deaths each year occur among these poor-prognosis cancers (Figure 2).

With this in mind, the primary key to reducing cancer deaths for Māori is by preventing the cancer in the first place (see above). If prevention is unsuccessful, then the next highest priority is early detection, when curative treatment is still possible. Once the cancer is diagnosed, the highest priority becomes ensuring access to timely best-practice treatment for the given tumour type and sub-type. Unfortunately, there is evidence that Māori are underserved in each of these post-diagnosis priorities.21,22 There are some burgeoning examples of high Māori screening participation in some regions (eg, the Southern DHB bowel screening programme), and these successes should be examined, documented and modeled where appropriate.

Early detection and screening

Early detection of primary lung cancer currently relies on either presentation of a patient with respiratory symptoms, or on chance findings following examination for other conditions (eg, chest x-ray for suspected heart disease). Given the poor prognosis of lung cancer, detection of tumours at the asymptomatic stage may increase the chances of survival via curative treatment. Studies investigating the efficacy of lung cancer screening via computed tomography (CT) scan have been promising.23–25 Preparatory lung cancer screening work is currently being completed in various locations throughout New Zealand, with the results of this preparatory work of critical importance to Māori health. National screening programmes for breast and colorectal cancers—both in the top three most common causes of cancer death for Māori—are in operation, although the latter programme is in its infancy and as of January 2020 was operational in 10 of the 20 district health boards.26 With evidence that Māori have poorer access to national screening programmes than non-Māori,27,28 there is an urgent need for renewed prioritisation and vigour in maximising Māori participation across these programmes.

Many of the most commonly diagnosed cancers among Māori are diagnosed outside of screening programmes. Diagnosis of these cancers principally relies on detection through primary care, although there is evidence that Māori are more likely to be diagnosed following acute admission at an emergency department.29 Maximising early diagnosis of cancers for Māori requires us to consider the key barriers to early diagnosis that Māori (to a greater extent than non-Māori) face. These include the financial burden of general practitioner visits, transport and travel, as well as other factors including patient comorbidity that may complicate diagnosis.30 In essence, we need to recognise that our current means of early detection systemically disadvantages Māori, and that this disadvantage contributes to the perpetuation of inequities in cancer death between Māori and non-Māori.

In terms of specific actions that impact on the cancers in Figures 1 and 2, the pathways for achieving important health gain for Māori will vary depending on the cancer. For example, an important pathway in terms of early detection of liver cancer for Māori is hepatitis surveillance. As noted above, hepatitis B and C appear to be the primary causes of liver cancer for Māori; however, Māori are underserved by the current national hepatitis surveillance programme. We previously observed that, in a cohort of Māori liver cancer patients with hepatitis B or C, only around 40% were on surveillance.31 Crucially, more than three-quarters (77%) of those not on surveillance were diagnosed with stage III or later disease, compared to 33% of those who were on surveillance.31 These observations, echoes of which can be observed across cancers, strongly suggest that careful scrutiny of the barriers to hepatitis surveillance could yield important health gains for Māori with liver disease.

Access to best-practice and timely treatment

There is compelling evidence that Māori have poorer access to timely best-practice treatment compared to non-Māori.21 For example, Stevens et al32 observed that Māori lung cancer patients were 60% less likely to be referred to a medical oncologist than non-Māori and were 70% less likely to receive curative treatment. Because we know that Māori have generally poorer access to best-practice and timely care, cancer care services have an important role to play in reducing the cancer burden for Māori.

In their global report on the drivers of social inequalities in cancer outcomes, the International Agency for Research on Cancer (IARC)4 summarised the key drivers of equitable access to cancer care as the following three A’s:

Availability: The physical availability of high-quality cancer care services, how well resourced and managed these services are, and how well they communicate with patients.

Affordability: The financial accessibility of the cancer treatment journey, from the costs of care to travel/transportation and loss of income.

Acceptability: How cancer care services are perceived by population groups, in terms of factors including effectiveness of care (ie, whether the care will actually work) and cultural competency of the system (ie, how similar/dissimilar the system is to your own culture).4

We can identify our own system within these three A’s, and how these are likely to be contributing to poorer cancer outcomes for Māori. Relevant factors include where services are located relative to where Māori live, the reality that some best-practice treatments are only available if privately funded, the inflexible nature of pathways of cancer care that do not necessarily reflect the priorities of Māori, and inadequate resourcing of Māori treatment providers and navigators.33 Each of these factors (and others) are important sources of disparities in access to care and poor cancer outcomes for Māori, and will be occurring to a different extent across cancer types. Underpinning the receipt of best-practice and timely care by Māori is the existence of standards of care (such as those recently published for colorectal cancer34) that clearly benchmark what a patient should expect to receive during their cancer care, and an unerring apolitical commitment to ensuring these standards are met for Māori across all district health boards in New Zealand.

Other opportunities for improvements in cancer outcomes for Māori

While we have focused in this manuscript on the cancers that present the greatest overall cancer burden on Māori, this does not detract from the importance of cancers that may be less common but will have equal impact at an individual (and whānau) level. For example, while the number of Māori female deaths from cervical cancer (11/year; Appendix Table 1) is far fewer than lung or breast cancers, the large survival disparity between Māori and non-Māori (adjusted HR: 1.4, 95% CI 1.1–1.8) suggests that there is room within existing systems for substantial improvement that will save the lives of Māori women. The advent self-testing kits for human Papilloma virus (HPV, the cause of all cases of cervical cancer9) will likely increase the uptake of cervical screening among those who did not previously access this screening.35 This is important, and might address the current substantial disparity in access to the national cervical screening programme among screen-age Māori women (64%) compared to European women (81%).28 Resourcing of cancer control initiatives aimed at reducing the cancer burden for Māori must take into account the burden of a given cancer, as outlined throughout this manuscript—but they must also remain flexible to ensure that we do not miss opportunities for relatively straightforward interventions (such as HPV self-testing) that will invariably save Māori lives.

Conclusions

In this manuscript we have presented the most commonly diagnosed cancers for Māori, the most common causes of cancer death, and contextualised survival disparities between Māori and non-Māori against the actual mortality burden of each given cancer. If our primary objective is to reduce the overall cancer burden for Māori, then our top priority may be preventing the majority of lung cancers via tobacco eradication while simultaneously detecting lung tumours early (possibly via a targeted lung CT screening programme). Population-based initiatives aimed at the prevention of cancers related to infectious diseases, diet, obesity and diabetes will also result in a substantial reduction in the incidence and mortality cancer burden for Māori. Likewise, overall improvements in early detection and the provision of best-practice timely treatment for Māori patients will close the survival gap between Māori and non-Māori in the short- to medium-term, leading to a further reduction in Maori cancer deaths.

Appendix

Methods

Data sources

We extracted all incident cases of cancer diagnosed between 2007–2016 from the New Zealand Cancer Registry (NZCR), which we then linked to the national Mortality collection to establish those patients that had died over the study period (for the purposes of survival analysis). In addition, to determine the number of cancer deaths for each given cancer we extracted all deaths where cancer was listed as the underlying cause of death from the Mortality Collection.

Variables

Ethnicity was derived from the NZCR for cancer incidence and survival analysis, and from the Mortality collection for mortality analysis. Those with Māori ethnicity were classified as Māori, while those without Māori ethnicity were classified as non-Māori. Cancer type (eg, lung cancer) was determined using ICD codes on the NZCR. In the case of breast cancer, only female breast cancer cases were included in analysis.

Descriptive analysis

In terms of descriptive analysis, we determined the top 10 cancers that were the most commonly diagnosed among Māori over the study period on the NZCR (ie, based on absolute counts). Similarly, we determined the top 10 most common cancers that were listed as an underlying cause of death on the Mortality collection. Further incidence, mortality and survival analysis was then conducted on these cancers.

Age- and sex-standardisation

We used direct age- and sex-standardisation to calculate standardised incidence rates (SIR) and standardised mortality rates (SMR),36 using the 2001 total Māori population as the standard.37 This method aligns with that used in the reporting for the WAI2575 report.38 For incidence, numerator data were the number of cases over the study period as determined from the NZCR. For mortality, numerator data were the numbers of deaths where a given cancer was listed as the underlying cause of death on the Mortality collection. In terms of denominators, we used aggregated estimated population data from Statistics New Zealand across the study period. Age- and sex-stratified denominator data for Māori were derived from mid-year Māori estimated residential population data,39 while non-Māori denominator data were determined by subtracting the Māori denominator data from the total mid-year estimated residential population data.40 When calculating temporal trends in incidence and mortality rates, we used the estimated residential populations for each respective year as the relevant denominator (eg, 2007 Māori estimated residential population when calculating 2007 incidence rate).

Where incidence and mortality rates are presented by sex in the Appendix, the denominator and standard population used for these rates is sex-specific. For temporal analyses, we calculated a Cochran-Armitage test for trend.

Survival analysis

Cox proportional hazards models were used to describe the extent to which Māori were more or less likely to die of their cancer than non-Māori, adjusted for age (continuous variable) and sex where relevant (categorical variable). These results were described using hazard ratios (HR), with non-Māori as the reference group.

All analyses were conducted in SAS v9.4 (SAS Enterprises Inc.) and Microsoft Excel 2016 (Microsoft Corporation).

Appendix Table 1: Numbers of Māori cancer cases (incidence) and the number of cancer deaths (mortality) per year, by cancer type.

Appendix Figure 1A: Age standardised incidence rate (SIR) for the top 10 most commonly diagnosed cancers among Māori females between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori females (bottom).

Appendix Figure 1B: Age standardised incidence rate (SIR) for the top 10 most commonly diagnosed cancers among Māori males between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori females (bottom).

Appendix Figure 2A: Age- and sex-standardised mortality rate (SMR) and absolute numbers of cases for the top 10 most common causes of cancer death for Māori females between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori population (bottom).

Appendix Figure 2B: Age- and sex-standardised mortality rate (SMR) and absolute numbers of cases for the top 10 most common causes of cancer death for Māori males between 2007–2016 (top), along with the age- and sex-standardised rate difference (RD) between Māori and the non-Māori population (bottom).

Appendix Table 2: Adjusted hazard ratios (HRs) and 95% confidence intervals, comparing the adjusted likelihood of cancer-specific death between Māori and non-Māori over the follow-up period. Total HRs are for combined sexes and are adjusted for age and sex, while sex-specific HRs are adjusted for age. HRs for cancers where fewer than 10 deaths occurred among Māori over the follow-up period are not shown.

Summary

Abstract

Cancer is an important cause of morbidity and avoidable mortality for Māori—and substantial disparities exist in cancer incidence, mortality and survival for Māori compared to non-Māori New Zealanders. In this viewpoint, we draw together cancer incidence, mortality and survival data from the previous decade, in order to provide clarity regarding the most important causes of cancer burden for Māori. Covering the decade 2007–2016, our manuscript directly leads on from the landmark Unequal Impact II report (which covered 1996–2006), and provides the most up-to-date record of this burden as is currently possible. While focusing on the absolute burden of cancer for Māori, we also compare this burden to that experienced by non-Māori, and consider how this relative disparity may (or may not) have changed over time. Finally, we discuss how to reduce the occurrence and the overall cancer mortality burden for Māori, with a focus on those cancers that confer the greatest burden.

Aim

Method

Results

Conclusion

Author Information

Jason K Gurney, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Hei Āhuru Mōwai (National Māori Cancer Leadership Group); Bridget Robson, Te Rōpū Rangahau Hauora a Eru Pōmare, Department of Public Health, University of Otago, Wellington; Jonathan Koea, Waitemata District Health Board, Auckland; Nina Scott, Hei Āhuru Mōwai (National Māori Cancer Leadership Group); Waikato District Health Board, Auckland; James Stanley, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Diana Sarfati, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, Wellington; Cancer Control Agency, Wellington.

Acknowledgements

We would like to thank Chris Lewis at the Ministry of Health for extracting the National Collections data presented in this manuscript. We gratefully acknowledge funding from the Health Research Council of New Zealand to support this work (HRC reference #: HRC 18/588).

Correspondence

Jason K Gurney, Cancer and Chronic Conditions Research Group, Department of Public Health, University of Otago, PO Box 7343, Wellington.

Correspondence Email

jason.gurney@otago.ac.nz

Competing Interests

All authors report grants from Health Research Council during the conduct of the study.

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