Regular screening for prostate cancer may have little effect on cancer mortality, according to a pair of clinical studies published last week. The studies have reignited a years-old controversy over whether screening is worthwhile. If a simple blood test can reduce your risk of dying from prostate cancer, why wouldn't you take it?
Because prostate cancer probably won't kill you, and the treatment is risky and unpleasant. Prostate cancer is extraordinarily common, even among men who never realize they have the disease. Autopsy studies find evidence of the condition in 27 percent of men over 50 and 63 percent of men over 80, yet the great majority of those people die from some other cause. Among men diagnosed with prostate cancer—a small number compared with the undiagnosed cases—the five-year survival rate is almost 99 percent. Many of these patients live for 30 years or more before dying of some other cause.
That's not to say that prostate cancer is completely benign. It kills about three men out of 10,000 per year, and aggressive forms spread to the bone, often leading to a very painful death. The problem is that there's no way to distinguish the unlucky patients from the many who would never even notice their prostate cancer, meaning that the vast majority of treatment is unnecessary.
Treatment for the condition can be quite dangerous in its own right. The least invasive option uses a drug to block the activity of testosterone, which might otherwise accelerate the growth of the cancer. Side effects include testicular shrinkage, feminization (hot flashes and enlarged breasts), and osteoporosis. Radiation therapy or brachytherapy can cause damage to adjacent tissue, such as the colon and rectum, which sometimes doesn't manifest until years after treatment ends. Surgery to remove the prostate can sever the nerve that enables men to have erections or can lead to urinary incontinence. Because of these risks, and the low mortality rate associated with prostate cancer, many have argued that it isn't worth it to test for the disease, even though the screening process involves little more than a low-risk blood test and the eminently safe (but anxiety-inducing) digital rectal exam. Physicians note that most patients, frightened by the idea of cancer, will elect for extreme and often ill-advised treatment.
The data reported last week are unlikely to quell the debate. The U.S. study, which showed no reduction in mortality as a result of screening, did not analyze a large number of prostate-cancer deaths, and there were some potential flaws in its design. For example, 52 percent of the people in the "control group" ended up being screened for cancer. The European study involved several different testing centers with divergent protocols. Moreover, because neither study exceeded 10 years in duration, the full benefits of the screening may not yet have materialized. Meanwhile, screening advocates note that deaths from prostate cancer in the general population have been declining by 4 percent per year since 1994, which coincides rather neatly with the FDA approval of the blood screening test.
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Explainer thanks Robert Faust of the University of Maryland Medical Center, Patricia Hoge of the American Cancer Society, and Jyoti Mathad and W.T. Oberle of Mercy Medical Center.