Prostate-specific antigen (PSA) screening and follow-up investigations in Māori and non-Māori men in New Zealand

Prostate cancer has been identified as the primary contributor to cancer burden in New Zealand men; with prostate cancer burden for Māori men being 50% higher compared with non-Māori men [1]. Māori men were reported to have higher mortality from prostate cancer, despite having lower incidence rates [2‐4].

Although screening for prostate cancer is not recommended in New Zealand due to the controversy about its harms versus benefits [5‐7], it is common in New Zealand general practice [8, 9]. Screening rates in New Zealand are similar to other countries with privatised primary care services, such as the USA, Canada and Australia [10‐12]. In 2010, approximately 80% of prostate-specific antigen (PSA) tests were undertaken in asymptomatic men [13], which means that by definition they were screening tests [14]. Despite the limitations of the PSA test when used as a screening tool, it is currently considered to be the best single test for early detection of prostate cancer [15].

A significant proportion of general practitioners (GPs) in New Zealand believes that screening for prostate cancer is beneficial [13, 16]. A recent study has found that 80% of PSA testing in New Zealand primary care was initiated by GPs, not by patients [13]. Similar screening behaviour and beliefs have been reported from other countries [17‐19].

In the USA, differences in screening practices, such as availability and interval of screening contribute to ethnic disparities in prostate cancer incidence and mortality [20]. It is unclear whether the low prostate cancer incidence and high mortality for Māori men are due to disparities in screening or biopsy rates, resulting in later tumour stage at diagnosis for Māori men, and/or over-detection of indolent cancers for non-Māori men.

An in-depth understanding of the patterns of PSA screening in primary care is needed in order to explain the differences in prostate cancer incidence and mortality between Māori and non-Māori men in New Zealand so that evidence-based interventions can be developed to eliminate unfair and avoidable inequities.

The aim of this study was to ascertain annual PSA screening rates for Māori and non-Māori men using computerised records from general practices linked with laboratory data. Men with elevated PSA result were followed-up to examine management pathways, including referral and biopsy rates by ethnicity. The influence of practice characteristics on difference in screening rates between Māori and non-Māori men was also explored.

Māori men were half as likely to be screened for prostate cancer compared with their non-Māori peers. Lower screening rates have been commonly associated with lower prostate cancer incidence rates [11, 20, 24, 25]. Several New Zealand studies have pointed out that incidence rates for prostate cancer are lower in Māori men compared with non-Māori men [26‐28]. Our population-based study is the first to show that lower PSA screening rates are a significant factor contributing to lower prostate cancer incidence rates for Māori men.

Only 2% of screened men had an elevated PSA, so an overwhelming majority was shown to have a normal PSA result. However, screened Māori men were twice as likely to have an elevated PSA result compared with non-Māori men. This finding may be partly due to the fact that Māori men were less likely to have been tested in the three years prior to 2010, implying that there is a greater potential for detecting prostate issues in Māori men compared with more frequently tested non-Māori men.

There were no significant differences in the rates of follow-up investigations and cancer detection between Māori and non-Māori men with an elevated PSA result. In general, 39% of men with an elevated PSA result were referred to a specialist in the follow-up period, meaning that the majority of these men were managed in general practice. One of the reasons why general practitioners (GPs) do not immediately refer men with elevated PSA result may be their awareness of the fact that an increase in PSA level can be caused by prostatic diseases other than prostate cancer, such as prostatitis and benign prostatic hyperplasia [29, 30]. GPs may feel that repeated PSA tests are needed to assess the actual risk of prostate cancer before referring to a specialist.

Overall, 67% of referred men went on to have a biopsy. It is recommended that the decision when to proceed to prostate biopsy should be primarily based on PSA level and the result of digital rectal examination, but other factors, including patient’s age, family history, and co-morbidities may be considered by the specialist [6, 31]. These factors may also influence GPs’ decision to refer for a specialist assessment in the first place.

In our study, there was a large variation between practices in PSA screening rates. This finding is consistent with studies from other countries [32‐34]. It has been shown that besides patient characteristics, such as age and co-morbidities, GP and practice characteristics, including the number of GPs in the practices and the number of patients seen by the GP influence screening behaviour [17, 35‐37]. In addition, studies on screening behaviour of physicians report that GPs believe in the benefits of PSA screening, which is probably one of the reasons why they commonly initiate it [13, 17, 35]. It has also been shown that GPs expressed difficulties in understanding and explaining to patients the complexities of screening for prostate cancer [13, 17, 38]. Such difficulties have been attributed to the lack of consensus in screening guidelines between different national organisations as well as internationally [18, 39]. For example, at the time of our research the Urological Society of Australia and New Zealand [40] has recommended that asymptomatic men aged 55-69 years should be offered a prostate-specific antigen (PSA) test and digital rectal examination (DRE) after the patients have been advised on the risks and benefits of PSA screening, while in contrast, the Ministry of Health (The National Screening Advisory Committee) has not supported population-based screening for prostate cancer [7].

In the vast majority of practices Māori men were less likely to be screened, however, two Māori provider practices showed relatively equal screening rates for Māori and non-Māori men. Concurrently, Māori provider practices showed the lowest overall screening rates among the 31 practices. Māori provider practices differed from other provider practices with respect to a higher proportion of Māori patients but they were also smaller in terms of both number of patients and GPs. With the knowledge that screening is mainly GP-driven, it is unclear why GPs are less likely to initiate prostate cancer screening for Māori men. More research is needed into reasons for the 50% lower screening rates for Māori versus non-Māori men in New Zealand.

This study makes an important contribution to New Zealand’s national dialogue on prostate cancer inequities between Māori and non-Māori men, prostate cancer screening and cancer inequities in general. We found that lower PSA screening rates in Māori men are a major determinant of a lower prostate cancer incidence. Due to potential harms of prostate cancer screening [7], it is not clear whether Māori men would benefit from increased screening rates. Māori men were more likely to have an elevated PSA result compared with non-Māori men, suggesting that a larger proportion of Māori men was at risk of prostate cancer compared with non-Māori men. There was a large variation in PSA screening rates among practices, with Māori provider practices showing the lowest overall screening rates. Although there were no differences between Māori and non-Māori men in the proportion of follow-up investigations, overall less than half of the men with an elevated PSA result were referred to a specialist for further examination. The large variation in screening patterns among practices may be partly attributed to inconsistent recommendations for screening by various organisations, but this argument would not hold for the observed differences by ethnicity. One recommendation that has been found to be consistent for a majority of organisations is that decisions around screening should be made following an in-depth discussion about the pros and cons of screening between the patient and his health care provider. Screening in New Zealand is currently mainly GP-driven, so there is obviously a need for more education for GPs, probably more discussion time between GPs and patients around screening and prostate cancer detection, and for strategies leading to improvements in health literacy, thereby creating an environment, in which shared decision-making between GPs and patients can be achieved.

More research is needed to better understand GP decision-making about screening pathways for prostate cancer, which will in turn help to further clarify the causes of higher mortality rates for Māori compared with non-Māori men with prostate cancer. To sum up, opportunistic screening is relatively common in New Zealand but varies widely by practice and ethnicity. Better understanding of prostate cancer risk on an individual basis, employing shared decision-making regarding screening and consistent follow-up strategies for men considered to be at higher risk of prostate cancer may help to target resources and thus improve outcomes, particularly for Māori men in the future. The ultimate goal should be to devise strategies for prostate cancer control that unite best practice, equity, and cost-effectiveness of health care services.