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| Journal of the New Zealand Medical Association,
20-June-2003, Vol 116 No 1176
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Screening for prostate cancer: a survey of New Zealand
general practitioners
John Durham, Melissa Low and Deborah McLeod
Prostate cancer is an important health issue for New Zealand
men. In 1999, the latest year for which complete figures are available, the
age-standardized rate for prostate cancer registrations was 98.2 per 100 000
population.1 It is the third most common cause
of cancer deaths in males, following lung and colorectal cancer, and accounted
for 14% of all male cancer deaths and 3.85% of all male deaths in 1999, with an
age-standardized mortality rate per 100 000 population of
18.5.2
There has been a rapid increase in the rate of new
registrations for prostate cancer since about 1991. New registrations increased
by 63% between 1993 and 1994, and 23% between 1994 and 1995. From 1995 to 1997
there was a 6.2% decrease in the annual rate of new registrations but the rate
increased again in 1999.1 The great majority of
new registrations in 1999 were based on a histological diagnosis. It is likely
that the specimens provided for most of these patients were taken from needle
biopsies of the prostate gland performed because of abnormal findings on digital
rectal examination (DRE) or prostate specific antigen (PSA) testing. More than
58% of all new registrations were in men aged more than 70 years. Prostate
cancer had a fatality/case ratio of 0.21, with nearly five times more
registrations than deaths. In 1999 there were a total of 552 deaths from
prostate cancer; 81.9% of these deaths were in men older than 70 years and 38.9%
in men older than 80 years.2
It is possible that this sudden and rapid increase in the
incidence of prostate cancer is a result of screening using the PSA test.
‘Screening’ refers to the application of a test to people who are as
yet asymptomatic for the purpose of classifying them with respect to their
likelihood of having a particular disease.3 In
1996, the New Zealand National Health Committee (NHC) sponsored a review by an
independent Prostate Cancer Screening Working Party of the potential risks and
benefits that might arise from prostate cancer screening. The Working Party
reported that there were significant potential risks associated with
confirmatory tests and treatment, and that these risks outweighed the as yet
unproven benefits of earlier intervention that would be achieved by screening
asymptomatic men for prostate cancer. A joint policy statement advising against
routine prostate screening for men without symptoms was issued publicly by the
NHC in New Zealand and the Minister for Human Sciences and Health in Australia
on 12 August 1996. The NHC recommended that:
‘Because screening has not
been demonstrated to improve the quality and length of men’s life through
early diagnosis, a systematic prostate cancer screening programme for men
without symptoms should not be introduced. The matter should be kept under
review.’4
At about the same time as the 1996 NHC recommendations, a
survey of 500 New Zealand general practitioners (GPs) reported the views and
practices of GPs in relation to screening for prostate
cancer.5 This study found that approximately
one third of GPs believed that no one should be screened using either the PSA
test or DRE and 40% of GPs felt that all men over 50 years in age should be
screened with one or other test. These results were similar to surveys in other
countries where primary care physicians had high and increasing rates of PSA
testing, with PSA tests forming part of the routine examination of men more than
fifty years of age.6,7
The aim of the current study was to determine whether the
rapid increase in the incidence of prostate cancer was consistent with GPs
continuing to undertake PSA screening, and to identify current practice with
respect to prostate cancer screening.
MethodsMedimedia, who have a
commercially available database of 2684 New Zealand GPs, provided a
computer-generated, random, national sample of 600 GPs. The sample was
stratified on the basis of postcodes to include equal numbers of rural and urban
GPs. The full Medimedia database consisted of 1603 GPs with an urban postcode
and 1081 GPs with a rural postcode. Twenty five GPs from the initial sample were
ineligible for the study, leaving a final sample of 290 urban and 285 rural GPs.
The reasons for exclusion of GPs from the sample were that 10 had left general
practice, four were on long-term leave and 11 were no longer at the address
provided.
The questionnaire used was developed specifically for this study and was piloted on a different sample of 10 GPs to ensure that it was understandable and had face validity. Screening behaviour was measured using closed questions about practice screening programmes, a series of case vignettes of typical screening situations, the performance of screening tests, risk factors for prostate cancer, and treatment options. The questionnaire defined ‘population screening’ as offering a test to all men of a certain age, ‘opportunistic screening’ as offering a test to men presenting with an unrelated problem, and ‘selective screening’ as testing men with specific symptoms or risks.3 Distribution of the questionnaire was initially by post. Non-responders received two reminder questionnaires; the first of these was posted and the second was sent by fax. The following are examples of the case vignettes used when asking GPs to indicate which screening tests, if any, they would use for some of the different possible presentations of men who might have prostate cancer:
The full
questionnaire is available on request from the authors.
The responses to all quantitative questions were coded and entered directly into a database. The results are presented as a frequency analysis of responses to each question. Where appropriate, statistical tests of independence of the categories in the frequency tables used were the chi-square test and the generalised Fisher exact (Fisher-Freeman-Halton) test. In order to account for the different proportions of urban and rural GPs, the response frequencies in each sample were weighted using the respective sampling fractions, and 95% confidence intervals (CI) were calculated when making inferences about the responses of all GPs. ResultsResponse
rate Responses were received from 381 (66.3%) of the eligible GPs. The
demographic information for the responding population is shown in Table
1.
Table 1. Demographics of the responding
population
The responders and non-responders were compared for gender
and year of registration. There were no significant differences in these
parameters between the responders and the non-responders.
Rural GPs were significantly more likely to work in a group
practice of four or more doctors compared with urban GPs (p = 0.0455).
Otherwise, there was no statistically significant difference between rural and
urban GPs for gender, age, years in practice or number of sessions worked per
week. Female GPs were significantly more likely than male GPs to be younger (p
<0.0001), and to have worked in general practice for a shorter period (p
<0.0001), with fewer GPs in the same practice (p = 0.0008) and for fewer
sessions per week (p <0.0001).
All responses were analysed for differences between urban
and rural GPs, and between male and female GPs. No statistically significant
differences were found except in the response to the question about the value of
the NHC guidelines. In the responses to this question female GPs were
significantly more likely not to have seen the guidelines (p =
0.0088).
Screening for prostate
cancer GPs were asked which tests they would perform for: a man
presenting for a general checkup with no significant family or medical history;
a man concerned about his risk of prostate cancer who has a brother with
prostate cancer and an aunt who had died of breast cancer in her forties; and a
man presenting for advice about prostate screening. Respondents could choose to
do more than one test and also had the option to do no tests. Answers to these
questions are shown in Table 2. The responses suggest that 73.7% (95% CI
69.3–78.2%) of GPs would do a PSA test as part of a health checkup and
74.5% (95% CI 70.1–78.9%) would do a PSA for a man asking about prostate
screening. This figure increased to 93.2% (95% CI 90.6–95.8%) of GPs who
would do a PSA test for the same man with a family history of prostate and
breast cancer.
Table 2. Use of screening tests indicated by
responders
In order to estimate how effective GPs felt that the
screening tests were in identifying asymptomatic prostate cancer, the
questionnaire asked respondents to provide an approximate estimate of the
positive predictive value (PPV) of these tests. Of respondents who replied, 27%
provided an estimate of the PPV for the PSA and DRE tests that agreed with the
levels reported in the literature.8 A majority
of the respondents (56.2%) overestimated the PPV for DRE, and more than one
third (36.0%) overestimated the PPV of the PSA test.
Screening programmes in
general practice The questionnaire asked GPs to indicate which, if any,
groups of patients they currently screened for prostate cancer and which types
of screening programmes they thought should be performed in New Zealand (Table
3).
Table 3. Screening programmes used and preferred in
general practice
*respondents were able to select more than one
option
This suggests that some form of screening programme is
offered by 97.5% (95% CI 96.0–99.0%) of all GPs and 50.0% (95% CI
45.0–55.2%) support a population-screening programme for prostate cancer.
Twenty six GPs claimed that they used all three types of screening in their
practice and only 25 GPs mentioned that there was no demonstrated benefit of
population screening for prostate cancer. Thirty six GPs said that their
practice offered screening for prostate cancer by the practice nurse, but only
nine of these GPs said that this involved a specific protocol for the use of
prostate cancer screening tests.
There was a range of opinion about which age groups should
be screened for prostate cancer in New Zealand. Most GPs thought it appropriate
to include men between 50 and 70 years, and relatively few GPs wanted to screen
men under 40 years or over 80 years (Table 4).
Table 4. Age groups felt to be appropriate for
screening by GPs
Fifty six per cent of the respondents
thought that the screening interval should
be two years and only 6% greater than two years.
GPs were also asked how useful they had found the NHC
guidelines on prostate screening. The guidelines were thought to be of some use
or better by 35% of the GPs who replied to the questionnaire, but 36% reported
not having seen the guidelines.
Risk factors for prostate
cancer Selective screening programmes depend on being able to identify
asymptomatic individuals who may be at risk of developing the target disorder.
The questionnaire asked GPs to identify a range of factors as either being of no
risk, low risk, or high risk in the development of prostate cancer. Most
respondents correctly identified increasing age (86.9%) and a first-degree
relative with prostate cancer (82.9%) as being associated with an increased
incidence of prostate cancer, but only 29.7% recognised the association with
breast cancer. High dietary fat intake was thought to be a risk factor by 45.9%
of respondents but smoking (62.9%) and benign prostatic hyperplasia (63.6%) were
incorrectly identified as risk factors by many GPs. The majority of respondents
were not sure about the significance of Maori (52.5%) and Asian (63.5%)
ethnicity as risk factors.
Follow up of abnormal tests
or after diagnosis of prostate cancer Two vignettes asked GPs which tests
they would use in men returning for follow up. The first of these was a man
returning one year after radiotherapy for prostate cancer, and the second was a
man returning after an abnormal PSA result of 6 ng/ml and a free PSA of 28%. In
the latter scenario, the PSA test would be repeated by 64% of the GPs, and the
other GPs would investigate the abnormal test by some combination of DRE,
transrectal ultrasound (TRUS) examination or specialist referral. More than 90%
of the respondents would order a PSA test as part of the follow up one year
after radiotherapy. A TRUS would be ordered by 27% of the GPs as part of the
investigation of the abnormal PSA.
Management of prostate
cancer An important part of any screening programme is the information
given to participants about their treatment options if they are found to have
the target disorder. The GPs were asked to suggest the most appropriate
treatment for men who had been found to have localised prostate cancer and were
thought to have either more or less than 10 years’ life expectancy (Table
5). ‘Other therapy combinations’ all included radical prostatectomy
and/or radiotherapy and hormone treatment.
Table 5. Suggested treatment of a man with localised
prostate cancer and less or more than 10 years’ life expectancy
For a man with less than 10 years’ life expectancy and
localised prostate cancer 68.5% (95% CI 63.8–73.2%) of GPs thought that
non-curative treatment (watchful waiting or hormone therapy) would be
appropriate. For the same man with more than 10 years’ life expectancy
only 11.1% (95% CI 7.9–14.3%) thought that this would be appropriate
management.
DiscussionThis survey found that 74% of GPs
in New Zealand say that they will do a PSA screening test for prostate cancer
when a 55-year-old man either asks about prostate cancer screening or has a
routine, annual health check. Ninety three per cent of GPs would do a PSA test
if this same man had a family history of prostate cancer. The survey also found
that nearly all GPs offer some form of prostate cancer screening and 50%
supported a national screening programme for prostate cancer. This increase in
the number of GPs who believe in the value of prostate cancer screening, since
the earlier survey by Morris,5 is consistent
with the observed sustained increase in the rate of new registrations for
prostate cancer.
Between 1993 and 2002 there have been at least 19 published,
systematic reviews of prostate cancer
screening.9 These reviews have consistently
concluded that there is no evidence that screening for prostate cancer will
reduce mortality, and that radical treatment of prostate cancer has a risk of
significant increased morbidity. It appears that the majority of New Zealand GPs
support a screening programme with no proven benefit and the potential to cause
considerable harm.
Pressure from groups outside general practice may be one
reason for this high level of screening. In responding to the questionnaire,
some GPs commented that the Prostate Awareness Society, the media and urologists
encouraged men to actively seek screening for prostate cancer. Another possible
explanation for the increased level of screening is that GPs feel that they
would be exposed to an increased risk of medical litigation if they discouraged
patients from having screening tests and these patients were subsequently found
to have prostate cancer. A study in Australia found that 61% of GPs thought that
they would be at risk if they did not screen an asymptomatic man requesting a
PSA test and that national evidence-based guidelines against prostate cancer
screening provided only limited medicolegal
protection.10
The best available estimates for disease-specific survival
for localised prostate cancer are in the region of 90% after 10
years.9 In the only reported randomized
controlled trial comparing radical prostatectomy with watchful waiting in early
prostate cancer there was no statistically significant difference in overall
mortality between the two groups after eight years of follow
up.11 This survey found that 42% of GPs would
recommend screening for men aged 70–79 years and only 2.9% of GPs would
consider watchful waiting for men with prostate cancer and more than 10
years’ life expectancy. These figures suggest that the information about
disease-specific survival for localised prostate cancer may not be well known or
understood by many GPs. However, there was a strong trend towards watchful
waiting in those men with a short life expectancy, and a more active approach of
prostatectomy and radiotherapy in those men with a greater life expectancy. GPs
may find it difficult to diagnose a condition and not treat it actively unless
there was a likelihood that the disease was not going to be the ultimate cause
of mortality.
Other results from this survey also suggest that GPs need
more information about the effectiveness of population screening for prostate
cancer. A few GPs expressed concerns about the accuracy of the available
screening tests, but only 27% were able to give a reasonable estimate of the
positive predictive value of the PSA test and DRE, and most overestimated the
accuracy of these tests. Age and a positive family history of prostate cancer
were correctly identified as risk factors by most GPs, but the majority were
uncertain about the relevance of other potential risk factors. The variation in
the responses to a PSA result of 6 ng/ml with a free-to-total PSA of 28% implies
some lack of understanding of the significance of the free-to-total PSA result
and the ‘normal’ range of the PSA test when used in a screening
programme.12 This result implies a reduction in
the probability of having prostate cancer from 1-in-5 with the PSA result alone,
to 1-in-12 with the additional free-to-total PSA result. It is doubtful if this
reduction in risk would persuade many men not to have a prostate biopsy. The
spontaneous variation in the PSA level between consecutive measurements within a
90-day period can be as much as 1 ng/ml.13
Repeating the screening test would still produce a result above the generally
accepted cut-off point of 4 ng/ml and no change in the risk of prostate cancer
indicated by the original test.
In general, this survey suggests that there is a clear need
for good, easily accessible information for both GPs and their patients about
the value of screening for prostate cancer and the interpretation of the results
of the available screening tests.
Author information:
John Durham, Senior Lecturer; Melissa Low, Medical Student; Deborah McLeod,
Research Manager, General Practice Department, Wellington School of Medicine and
Health Sciences, University of Otago, Wellington
Acknowledgements:
This survey was carried out as a summer studentship by Melissa Low, funded by
the New Zealand Guidelines Group. We are grateful to all GPs who completed the
questionnaire.
Correspondence: Dr
John Durham, Ora Toa Medical Centre, 227 Bedford Street, Cannons Creek, Porirua.
Fax: (04) 237 5925; email: john.durham@oratoa.co.nz
References:
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