Prostate Cancer Screening Trials Results Announced

Two large scale trials, one American, one European, published their mortality results in the New England Journal of Medicine today. The results of these trials have been eagerly awaited with the hope that they may finally answer the question of whether screening for prostate cancer saves lives.

The European study of 182,000 men (Schroder et al), aged 50-74 years randomized to be offered a PSA test every 4 years, or no such screening, reported a lower risk of prostate cancer death compared with the control group (0.80, p=0.04) after a median of 9 years followup. The absolute risk difference was 0.71 deaths per 1000 men or a reduction of 20%. The authors say that to achieve this benefit, there is a high cost: “1410 men would need to be screened and 48 additional cases of prostate cancer treated to prevent one death from prostate cancer”. (This is similar to the numbers needed to treat to save one death in studies of mammographic screening for breast cancer and fecal occult blood testing for colorectal cancer). The reduction in death rates was restricted to men between the ages of 55 and 69 years when the study commenced.

In the US study (Andriole et al), 76,693 men were randomized to receive annually screening or usual care, which could include screening. Compliance with screening was 85% in the treatment group and 46-52% received PSA screening in the control group also. After a median 11 years of followup the death rate from prostate cancer did not differ in the two groups. The authors point out that the high level of screening in the control group could have diluted a modest effect of screening in the screened group. To be considered screened in the control group men must have been tested within 12 months, a much tighter requirement than the 4 yearly screening tested in the European trial. It is thus possible that ‘PSA contamination’ in the control group may have been even higher than the 52% reported. The authors say that it is also possible that improvements in treatment during the study period may also have blunted differences in death rates between the two groups.

The two trials thus do not yet resolve the controversy about the effectiveness of PSA screening in reducing deaths from prostate cancer. As the follow-up period is extended into the future, however, it is possible that any mortality differences may become clearer. Nevertheless the high cost of screening in terms of services and morbidity experienced by the large numbers men who are biopsied and treated is clear from these studies. Commentators still advise that men make their own, informed decision about whether to be screened.

www.nejm.org

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