PSA screening of asymptomatic men reduced risk of metastatic prostate cancer by 35 per cent

Jul 11 2005

Early screening of prostate cancer in asymptomatic men may reduce their risk of death from metastatic prostate cancer by as much as 35 per cent, researchers from the University of Toronto have found.

"Early screening with the prostate specific antigen (PSA) is quite controversial. There are many arguments both for and against the efficacy of this form of early screening," says Vivek Goel, professor of public health sciences and health policy management and evaluation at U of T and one of the senior authors of the study. "Our study shows a fairly significant benefit, and this benefit is demonstrated even among men who were not screened regularly as part of a screening program. There may be greater benefit from an organized screening program."

Published in the August issue of the Journal of Urology, Goel and Jacek Kopec, a professor at the University of British Columbia, did much of this work while both were part of U of T's public health sciences department. The researchers conducted a population-based case control study in the Greater Toronto Area of 236 men with advanced metastatic prostate cancer and a control group of 462 men who did not have metastatic prostate cancer. From 1999 to 2002, they matched subjects on age and area of residence and obtained self-reported information about their lifestyles, health history and utilization of health services. The researchers also received permission to review medical records and history of screening.

They found that PSA screening of asymptomatic men reduced their risk of metastatic prostate cancer by 35 per cent.

In North America, prostate cancer is the most frequently diagnosed cancer in men and the second leading cause of death by cancer in men, often as a result of the cancer spreading or metastasizing to other parts of the body. PSA tests are simple blood tests that detect an antigen in blood. While small amounts of this antigen are normal, higher levels could indicate problems like prostate cancer.

The controversy surrounding early PSA screening deals with false positives generated by high PSA scores. Hidden or localized prostate cancer does not always metastasize and people with this localized cancer may go on to live normal lives for years without incident.

"Just by chance alone you're going to be picking up some of those prostate cancers, and those people wind up getting labeled as prostate cancer patients," states Goel. "They get treatments for it, surgery, radiation, chemotherapy, hormonal therapy – all of which have side effects – not to mention the anxiety and angst associated with having prostate cancer as a label. But the reality also is that they may never have actually died of the prostate cancer because it was so localized."

When they compiled data results, Kopec and Goel, both of whom are public health epidemiologists, say they were surprised by the size of the protective effect. "What usually happens with tests like these is that clinicians tend to be very supportive while public health people tend to be more cautious," says Kopec. "The clinical members of our study team feel that these findings are confirming what they had believed all along; we were a bit more surprised. A 35 per cent difference is quite a large amount so from our perspective it is quite a significant link in the chain supporting that early prostate screening has a positive impact."

Ontario is among the half of Canadian provinces that does not cover the costs of PSA screening tests. Guidelines for physicians in Ontario recommend that men over 50 should be informed of the health risks and benefits of early screening by their family physician.