Prostate cancer screening has yet to prove its worth
(29 June 2009: VIDYYA MEDICAL NEWS SERVICE) -- The recent release of two large randomized trials suggests that if there is a benefit of screening, it is, at best, small, says a new report in CA: A Cancer Journal for Clinicians. Authored by Otis W. Brawley, M.D. of the American Cancer Society and Donna Ankerst, Ph.D. and Ian M. Thompson, M.D. of the University of Texas Health Science Center at San Antonio, the review says because prostate cancer is virtually ubiquitous in men as they age, it is clear that a goal of "finding more cancers" is not acceptable. Instead, public health principles demand that screening must reduce the risk of death from prostate cancer, reduce the suffering from prostate cancer, or reduce health care costs when compared with a non-screening scenario. The authors suggest prostate cancer screening has yet to reach one of these standards to date.
No major medical group, including the American Cancer Society, currently recommends routine prostate cancer screening for men at average risk. In the United States, prostate cancer will affect one man in six men during his lifetime. Since the mid-1980s, screening with the prostate–specific antigen (PSA) blood test has more than doubled the risk of a prostate cancer diagnosis. The review says a decrease in prostate cancer death rates has been observed since that time, but the relative contribution of PSA testing as opposed to other factors, such as improved treatment, has been uncertain.
The report says a computer modeling study using National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) registries estimated that more than one in four cancers detected in whites (29 percent) and nearly half of cancers detected in blacks (44 percent) were overdiagnosed cancers. A similar model using data from Europe estimated a 50 percent overdiagnosis rate. The authors say patients who are diagnosed with clinically insignificant tumors are subject to unnecessary diagnostic tests and unneeded treatment and suffer psychosocial harms. They are also labeled "a cancer patient," which can have negative economic consequences. Also, say the authors, overdiagnosis significantly affects 5–year survival statistics, making them uninformative in demonstrating progress in cancer control.
The report says the future of prostate cancer will include better screening tests, better methods to assess a man's risk of prostate cancer, and prevention strategies, including the use of finasteride, a drug currently used for the treatment of urinary symptoms related to prostate enlargement.
In a separate but related editorial, Peter Boyle, Ph.D., D.Sc., of the International Prevention Research Institute, Lyon, France and report co-author Dr. Brawley say "the real impact and tragedy of prostate cancer screening is the doubling of the lifetime risk of a diagnosis of prostate cancer with little if any decrease in the risk of dying from this disease." They say in 1985, before PSA screening was available, an American man had an 8.7 percent lifetime risk of being diagnosed with prostate cancer and a 2.5 percent lifetime risk of dying from the disease. Twenty years later, in 2005, an American man had a 17 percent lifetime risk of being diagnosed with prostate cancer and a 3 percent risk of dying from the disease. They add that even in the best case scenario, applying the findings of a European trial that found PSA led to a 20 percent reduction in the risk of death, the average man who chooses screening decreases his risk of prostate cancer death from a lifetime risk of 3 percent to a lifetime risk of 2.4 percent. In exchange, he doubles the chances of becoming a prostate cancer patient, his risk of diagnosis rising from about nine percent to at least 17 percent.
They conclude that "men should discuss the now quantifiable risks and benefits of having a PSA test with their physician and then share in making an informed decision," and that "the weight of the decision should not be thrown into the patient's lap."
Article: "Screening for Prostate Cancer," Otis W. Brawley, MD; Donna Ankerst, PhD; and Ian M. Thompson, MD, CA Cancer J Clin, July/Aug 2009 doi:10.3322/caac.20026.
Editorial: "Prostate Cancer: Current Evidence Weighs Against Population Screening," Peter Boyle, PhD, DSc; Otis W. Brawley, MD, CA Cancer J Clin, July/Aug 2009 doi:10.3322/caac.20025.
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