Prostate cancer screening in the general population is likely to reduce disease-specific deaths by less than a third, according to results from a 20-year Swedish study.
The findings, published March 31 in BMJ, involve the longest follow-up of any prostate cancer screening study to date, thanks in part to the ease of tracking Swedish patients through national databases and registries (BMJ 2011;342:d1539 [doi:10.1136/bmj.d1539]).
For their research, Dr. Gabriel Sandblom of the Karolinska Institute, Stockholm, and his colleagues examined results from a study enrolling 9,026 randomly selected men, aged 50-69 years, in Norrköping, Sweden. The study began in 1987, with every sixth man, or 1,494 in all, randomized to undergo prostate cancer screening every 3 years. The first two screenings used digital rectal examination only; in subsequent screenings, prostate-specific antigen testing was added. Men in the control group (n = 7,532) were not invited to be screened.
For the fourth and final screen in 1996, only subjects aged 69 years or under were invited. All men with cancer diagnosed up to Dec. 31, 1999, were included in the analysis, and survival was followed through the end of 2008.
The investigators found that more cancer was detected in the screened group (5.7%) than in the control group (3.9%), and that a significantly greater proportion of men in the screened group (56.5%) had localized tumors than in the control group (26.7%). Disease-specific mortality was 35% for men diagnosed in the screening group and 45% for controls; overall mortality for men with prostate cancer was 81% in the screening group and 86% in controls.
The risk ratio for death from prostate cancer was 1.16 (95% confidence interval 0.78-1.73), which the investigators noted was similar to that found in earlier, larger studies of shorter duration.
"The confidence interval of the risk ratio was narrow enough to conclude that screening and treatment of men with tumors detected through screening as practiced in the present study are unlikely to reduce mortality from prostate cancer by more than a third," they wrote. "Though screening could lead to a reduction of up to a third in mortality from prostate cancer, this would be at the risk of overdetection and overtreatment."
Dr. Sandblom and his colleagues recommended in their analysis that before undergoing prostate-specific antigen testing, "asymptomatic men should be informed about the potential hazards of treatment with curative intent in case prostate cancer is diagnosed." These hazards, they wrote, include erectile dysfunction, urinary incontinence, bowel symptoms, discomfort, and psychological stress.
The investigators cited as strengths of their study the low dropout rate; high compliance of their subjects; uniform treatment; complete data on tumor stage and grade; and detailed information on cause of death, thanks to comprehensive government registries and databases. The investigators acknowledged that although the size of the study population was not sufficient to draw definite conclusions, it was enough "to show major differences in prostate cancer–specific survival."
The study was funded by Swedish government agencies. Dr. Sandblom and his colleagues declared no conflicts of interest.