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Prostate specific antigen for early detection of prostate cancer: longitudinal study
British Medical Journal, 10/08/09

Holmstrom B et al. – No single cut–off value for prostate specific antigen concentration attained likelihood ratios formally required for a screening test. Prostate specific antigen concentrations below 1.0 ng/ml virtually ruled out a prostate cancer diagnosis during the follow–up. Additional biomarkers for early detection of prostate cancer are needed before population based screening for prostate cancer should be introduced.

Exclusive Author Commentary
Mattias Johansson, IARC, Lyon, 10/09/09

Albeit frequently practiced in today's healthcare, opportunistic PSA screening for prostate cancer in asymptomatic men remains a controversial subject. Whilst there is little doubt that the PSA test can assist physicians as one of several diagnostic tools, there are a number of aspects to consider before advocating mass screening. These include the validity of the actual screening test, availability of effective treatment, side effects from treatment, financial cost, and ultimately whether there is a measurable reduction in mortality in a screened population. In the study recently published in British Medical Journal we investigated the validity of the PSA-test in prediction of future prostate cancer diagnosis. The most important finding of our study was that no single cut-off for prostate-specific antigen (PSA) attained likelihood ratios formally required for a screening test. The direct implication of our findings in a screening situation is that no matter which PSA cut-off you adopt for selecting men for further diagnostic work-up, you will either have too many false positives, or too many false negatives. We also demonstrated the difficulties inherent to PSA testing graphically by the largely overlapping PSA distributions for prostate cancer cases and healthy men (see figure 1 in publication). In order to increase the sensitivity of the PSA-test recommendations tend now to suggest to lower the PSA cut-off to about 3 ng/mL, or even lower. Whilst this approach arguably will detect more cancers, it will also increase the number of false positives. We estimated that the proportion of false positives using a cut-off of 3 ng/mL would be 13%. Given that 5% of false positives is usually considered a maximum for population screening of asymptomatic subjects, it is clear that an unacceptable number of healthy men will be subject to painful, stressful and costly diagnostic procedures. In addition, and perhaps more serious, is the significant overdiagnosis of slow growing tumors causing unnecessary medical treatment and anxiety. This is in line with a recently published report from the European Randomized Study of Screening for Prostate Cancer where an aggressive approach was adopted with a PSA cut-off of 2.5-3 ng/mL in the screening arm. Whilst they noted a slight, but measurable, reduction in prostate cancer mortality in the screening arm, it came at the cost of a high risk of overdiagnosis. Curative treatment such as radical prostatectomy (surgical removal of the prostate gland) is associated with significant side effects including a high risk of erectile dysfunction and a small risk of severe urinary incontinence. In order to further assess the cost of overtreatment and overdiagnosis thorough quality-of-life evaluations are essential, both for men undergoing curative treatment, men on active monitoring, as well as regarding the psychological implications for men presenting with elevated PSA levels but without a cancer diagnosis. Follow-up reports on quality-of-life are expected from screening trials. Studies evaluating the financial implications of PSA screening will also be useful for policy and decision makers. Based on our findings, taken together with the results of the screening trials, we concluded that further biomarkers and diagnostic tools are needed before population based PSA-screening of healthy men can be recommended. In particular tools that help distinguish rapidly growing and potentially lethal tumors from slow growing tumors are warranted in order to minimize overdiagnosis and overtreatment. Furthermore, efforts should be made in informing the general public - as well as the treating physicians - of the benefits and risks of PSA testing and such information should be given to a man before the actual PSA-testing takes place. It is important that every man who considers PSA-testing is aware of the relatively modest chance of gain in survival, and the high risk of a sequence of tests and treatments that he might have been better served without.