21st September 2018, Volume 131 Number 1482

Sam Rice, Lifeng Zhou, Richard Martin

Melanoma in situ (MIS) refers to melanoma that is confined to the epidermis. The incidence of melanoma in situ varies throughout the world as it does for invasive cutaneous melanoma. It is associated with excellent outcomes, the 10-year survival of 100% for those treated with adequate excision. Many of those untreated will go on to develop invasive melanoma with a worse prognosis.1

Worldwide, incidence of invasive melanoma and melanoma in situ continued to increase during the 20th century but there is suggestion that it may be stabilising in the early 21st century.1–7 It is hoped that prevention programmes initiated in the past will result in a decrease in incidence in the next 10–20 years.

Relative rates of MIS compared to invasive melanoma have been increasing with the postulate that this is because of earlier detection programmes. Australia and New Zealand have the highest rates of melanoma in the world.7–9

There is no previously published data on melanoma in situ (MIS) in New Zealand. Further information is needed to allow comparison to similar information on invasive melanoma and lead to better understanding of the disease spectrum.

Methods

This research was registered and approved with the local ethics group. De-identified data were obtained from the New Zealand Cancer Registry (NZCR) by way of computerised search for MIS diagnosis. Inclusion criteria were all cases of MIS from NZCR files over a five–year period from 2008 to 2012.Exclusion criteria were incorrect or absent information, overseas residence, benign naevi and invasive melanoma. Only one diagnosis was allowed per patient per year to avoid duplication.

A separate search was also performed to identify all patients with a first diagnosis of invasive melanoma over the same time period.

The populations projected by Stats NZ were used as the population at risk for each year.1 World Health Organization standard population was used for calculating age standardised rates (ASR). Life table data were used to estimate lifetime risk. Age standardised rate and its 95% CI were calculated. Negative binomial regression and Poisson regression models with adjustment for overdispersion were run. Sex difference in the incidence rate of MIS was tested using negative binomial regression models stratified by age groups. SAS 9.3 was used in the statistical analysis.

Results

There were 10,879 cases of MIS and 11,354 cases of invasive melanoma diagnosed in New Zealand for the years 2008–2012 (Table 1 and Figure 1). There was a trend to increasing cases of MIS, but a relative plateauing of invasive melanoma. The number of cases for MIS overtook invasive melanoma in 2012.

Table 1: Total number of cases of melanoma in situ and invasive melanoma in New Zealand 2008–2012.

Diagnosis year

MIS cases

Invasive melanoma cases

2008

2,007

2,264

2009

2,039

2,212

2010

2,263

2,347

2011

2,220

2,206

2012

2,346

2,325

Total (2008–2012)

10,879

11,354

Figure 1: Total number of cases of melanoma in situ and invasive melanoma in New Zealand 2008–2012.

c 

For MIS, females made up 46.5% (5,059). The median age of women at the time of diagnosis was 61 years (14–99 years) and it was 66 years for men (15–96 years). The majority of the cases (98.6%) were European. District health board (DHB) showed Canterbury and Waitemata DHB accounted for more than 25% of the total cases (Table 2).

Table 2: General characteristics of the patients with melanoma in situ in New Zealand 2008–2012.

Characteristics

Number of cases

Proportion (%)

Diagnosis year

2008

2,007

18.45

2009

2,039

18.74

2010

2,263

20.81

2011

2,220

20.66

2012

2,346

21.37

Gender

Female

5,059

46.54

Male

5,820

53.46

Ethnicity

Māori

135

1.19

Pacific Island

8

0.07

Asian

15

0.13

European

10,727

98.61

DHB

Auckland

826

7.91

Bay of Plenty

979

9.37

Canterbury

1,409

13.17

Capital and Coast

272

2.6

Counties Manukau

782

7.49

Hawkes Bay

458

4.39

Hutt Valley

121

1.16

Lakes

236

2.26

MidCentral

646

6.19

Nelson Marlborough

453

4.34

Northland

296

2.83

South Canterbury

201

1.92

Southern

511

4.89

Tairawhiti

224

2.14

Taranaki

285

2.73

Waikato

831

7.96

Wairarapa

158

1.51

Waitemata

1,365

12.55

West Coast

84

0.8

Whanganui

395

3.78

The age standardised rate (ASR) is shown in Figure 2.

Figure 2: Melanoma in situ incidence rate (ASR, per 100,000) in New Zealand by year (2008–2012).

c 

There was an increase in incidence of MIS over the study period but this was not statistically significant (P=0.097). Overall, men had a significantly higher incidence compared to women.

However, in the younger age groups (<60 years old), women had a higher rate of MIS than men (P<0.0001), whereas men’s rate was higher in the older age groups (P<0.0001, see Figure 3).

Figure 3: Melanoma in situ incidence rate (per 100,000) by age group in New Zealand. 

c 

There was a significant difference in the incidence rate (ASR, per 100,000) between women and men for each body region (Figure 4). Men had higher rates than women in ‘head/neck’ (12.9 vs 7.7, p<0.001) and ‘trunk’ (14.6 vs 7.0, p<0.001), while women had a higher rate than men in ‘limbs’ (17.6 vs 11.4, p<0.001). Poisson regression models were also run indicating gender and body region were significant factors affecting the incidence rate, after adjusting for age group.

Figure 4: MIS incidence rate (ASR, per 100,000) by body region and gender over five years.

c

Overall, 31% of MIS lesions were located on the head and neck regions, 29% on the trunk and 40% on the limbs regions.

The national incidence rate (ASR) was 35.4 per 100,000 (95%CI: 34.7, 36.1) for the time period of 2008–2012 (Figure 5). Incidence rates varied markedly between DHBs with Whanganui having the highest (86.2 per 100,000) and Hutt Valley having the lowest (12.2 per 100,000).

Figure 5: Melanoma in situ incidence rate (ASR, per 100,000) by DHB in New Zealand. 

c 

Discussion

There has been statutory notification of cancer in New Zealand since 1994 and thus the data reported here appears valid. However, there is always potential for incomplete reporting of the diagnosis or pathological overcalling or undercalling of lesions, eg, dysplastic naevus versus MIS. It is possible that some pathologists are unaware of the mandatory reporting of MIS to the NZCR.

Those of European ethnicity made up 98.6% of cases, though they account for only 67% of the population. This is similar to that of invasive melanoma previously reported,7 confirming that MIS and invasive melanoma are a major problem for people of European descent. The true incidence rates are obscured by using the WHO age standardisation but allows for international comparison.

The median age at diagnosis was 61 years for women and 66 for men. While no direct comparison can be made, this appears to be somewhat older than previously reported rates of MIS in Australia, 51 and 56 years respectively.3

MIS incidence rates continued to increase over the five-year period of the study, while the incidence of invasive melanoma may be plateauing. Total MIS cases overtook invasive melanoma cases in 2012. Previously published rates for MIS and invasive melanoma had shown large increases in rate over time.4–6 It may well be that public education programmes that have been ongoing for at least 30 years are beginning to show population effects with earlier detection of lesions as MIS rather than invasive melanoma. However, there may also be an increasing false positive rate for dysplastic naevi being overdiagnosed as MIS.2

Preventative measures may also be contributing to stabilisation of invasive melanoma rates and hopefully decreases in the future.11

Older males remain the highest risk group with twice the incidence compared to females beyond age 70. This is consistent with previous reports of MIS and invasive melanoma.3,7–9,12,13

Incidence rate by body region demonstrated men had significantly higher rates than women in ‘head/neck’ and ‘trunk’, while women had a significantly higher rate than men in ‘limbs’. This is consistent with previous reports of both MIS and invasive melanoma.5,7

There was quite marked variation between incidence in different geographical regions as defined by DHB catchment areas. Canterbury and Waitemata DHBs had the highest overall numbers of cases in Table 2, though this is likely because these DHBs have the highest populations.10 This is reflected in the incidence rates by DHB in Figure 5 which show Canterbury and Waitemata have similar incidence rates, whereas eight other DHBs to have higher incidence rates despite lower overall numbers of cases.

The explanation for these differences may be due to incomplete reporting of MIS to the New Zealand Cancer Registry if there is misunderstanding to report only invasive melanoma rather than MIS (even though MIS reporting is mandatory).

The other possibilities include more access to skin cancer professionals in certain regions of New Zealand, variations in ethnicity and the different UV environments over the wide latitude spread in New Zealand. Though once again Whanganui has the highest incidence of MIS and invasive melanoma in New Zealand.

The national incidence rate (ASR) for MIS in New Zealand is approaching 39/100,000. This is similar, although slightly higher than MIS rates in Australia (approaching 37/100,000), which seems to be demonstrating a decline in melanoma incidence due in part to successful sun awareness programs.3,13 These rates are much higher than those reported in other countries in the world such as the US (14/100,000)14 and Sweden (10/100,000),15 which have an incidence of less than half that in New Zealand.

For MIS in New Zealand the lifetime risk for men was 6.0% and 4.6% for women during 2008–2012. The invasive melanoma risk is 7.7% for men and 5.6% for women.7 This gives a lifetime risk in New Zealand for melanoma (in situ and invasive disease) of 13.7% in men and 10.2% in women. There were 324 deaths from melanoma in 2012 in New Zealand.16

The reasons for New Zealand having the highest rates of MIS and invasive melanoma in the world are thought to include a fair-skinned population living at unusual latitudes, the ozone hole (although this is predicted to regenerate by 2050), intermittent sun exposure due to inclement weather patterns and lack of pollution (which absorbs UV radiation). We predict MIS incidence will continue to overtake invasive melanoma. Public education strategies may be beginning to show effect as well as doctors upskilling in knowledge and techniques such as dermoscopy and best skin cancer management.

Conclusion

This paper provides new information about the epidemiology of MIS in New Zealand and its relevance to clinical practice. This study suggests that while the rate of MIS is rising and the rate of invasive melanoma may be plateauing, it is hoped that this will eventually translate into lower melanoma mortality rates as melanomas are diagnosed at an earlier stage (thinner Breslow thickness and in situ disease). Prevention, awareness and early diagnosis must continue to be emphasised so that more MIS or thin melanomas are diagnosed and treated, allowing the mortality from melanoma to decrease.

Summary

Melanoma in situ (MIS) is associated with excellent outcomes, however many of those untreated will go on to develop invasive melanoma with worse outcomes. In this study, there were increasing numbers of people diagnosed with MIS, while numbers of people diagnosed with invasive melanoma remained steady. Overall, men were significantly more likely to be affected compared to women. Public education campaigns may be showing an effect with increasing prevention and earlier detection of MIS. It is hoped earlier detection and improved treatments will decrease the chances of death and disability from melanoma.

Abstract

Aim

The incidence of melanoma in situ varies throughout the world. It is associated with excellent outcomes, however many of those untreated will go on to develop invasive melanoma with a worse prognosis. There is no previously published data on melanoma in situ (MIS) in New Zealand. Further information is needed to enable better understanding of the disease spectrum.

Method

De-identified data were obtained from the New Zealand Cancer Registry (NZCR) by way of computerised search for MIS diagnosis. A separate search was performed to identify all patients with invasive melanoma. World Health Organization standard population was used for calculating age standardised rates.

Results

There was a trend to increasing cases of MIS, but a relative plateauing of invasive melanoma. The number of cases for MIS overtook invasive melanoma in 2012. Overall, men had a significantly higher incidence compared to women. Incidence rates varied markedly between different regions of the country.

Conclusion

This paper provides new information about the epidemiology of MIS in New Zealand and its relevance to clinical practice. Public education strategies may be beginning to show effect with the goal of increasing prevention and earlier detection and treatment to enable decrease in melanoma mortality.

Author Information

Sam Rice, Department of Surgery, Lyell McEwin Hospital, Adelaide, South Australia; 
Lifeng Zhou, Planning and Funding, Waitemata District Health Board, Auckland; 
Richard Martin, Department of Surgery, Waitemata District Health Board, Auckland.

Correspondence

Dr Samuel Rice, Department of Surgery, Lyell McEwin Hospital, Adelaide, South Australia.

Correspondence Email

samuel.rice@sa.gov.au

Competing Interests

Nil.

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