by ecancer reporter: Clare Sansom

The US Preventive Services Task Force (USPSTF) is charged with making recommendations for the use of clinical services in preventive medicine, such as screening. Each of their recommendations is based on a systematic, evidence-based review, weighing up the balance between the benefits and harms of a particular procedure.

In October 2011, the USPSTF released its recommendations for the use of the prostate-specific antigen (PSA) test for screening for prostate cancer; controversially, this recommended that the test should not be used in any age group. Roger Chou of Oregon Health & Science University, Portland, Oregon, USA and Michael LeFevre of University of Missouri School of Medicine, Columbia, Missouri, USA have now written a commentary on these recommendations for the Journal of the American Medical Association.

In this, they explore the evidence for the recommendations, examining whether the evidence used in the review has under-estimated the benefits or over-estimated the harms associated with the PSA test for prostate cancer.

Chou and LeFevre first explore the reported evidence for the benefits provided by prostate cancer screening. This used prostate cancer specific mortality as the primary benefit and assessed the results from two large, high-quality trials of the PSA test - the European Randomized Study of Screening for Prostate Cancer (ERSPC) and the US Prostate, Lung, Colorectal, and Ovarian (PLCO) cancer screening trial – that appeared to report conflicting results.

Both trials reported results that failed to reach statistical significance, with the ERSPC trial reporting a small decrease in mortality risk with screening and the PLCO trial an even smaller increase in risk. Problems were reported with the methodology of both trials, particularly in the PLCO trial with the high proportion of men in the no-screening group who had PSA testing outside the trial and in the ERSPC trial with the screened and non-screened groups receiving different treatment.

However, it was not possible to discern whether these were responsible for the difference in the reported results.

Other evidence provided for the benefit of screening that was used to form the USPSTF recommendations included the Gőteborg report, which shows a statistically significant benefit from screening but could be largely discounted as it is not independent of the ERSPC study, and epidemiological findings.

There has certainly been a substantial decrease in prostate cancer mortality over recent decades, but this began before screening was widely introduced and could be assumed to be mainly due to other factors, particularly improvements in the treatments available.

They then discuss the harms caused by PSA screening as presented in the USPSTF recommendations. There is no doubt that the standard treatments for localised prostate cancer, surgery and radiotherapy, can be associated with occasional peri-operative death and with significant morbidity including cardiovascular complications, urinary incontinence and erectile dysfunction.

Men who are treated un-necessarily for very slow-growing prostate cancers detected through screening are at risk of these. In the US, about 75% of men with low-risk cancers are treated by one of these modalities. A more judicious use of such treatments, with active surveillance or “watchful waiting” considered for a higher proportion of men with low-risk cancers, would be likely to reduce these harms. 

Chou and LeFevre concluded their commentary by saying that the value of prostate cancer screening would remain controversial, and that, regardless of the USPSTF recommendations, some men would continue to be offered and accept screening.

Furthermore, they recommended that men should be advised of the benefits and risks of screening; that no-one should be screened without his informed consent; and that a more selective use of risky, curative procedures in men with low-risk disease would reduce screening-associated harms and, therefore, increase the relative value of the test.

Reference

Chou, R. and LeFevre, M.L. (2011). Prostate Cancer Screening – The Evidence, the Recommendations, and the Clinical Implications. JAMA 306(24), 2721-2. doi: 10.1001/jama.2011.1891