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Monday, May 4, 2009
At first glance, it makes perfect sense.
Cancer is a disease characterized by growth; its extent typically indicates its severity. Screening to detect cancer early on, then, would seem like a logical preventative measure. In many cases, however, mass screening for early detection has little to no demonstrated value. Prostate cancer is one such case.
Pros and cons of screening
Physicians and scientists have long debated the benefits of routine prostate cancer screening. At present, most major medical associations, including the American Cancer Society, the American Urological Association and the U.S. Preventive Services Task Force, do not advise routine prostate cancer screening. Instead, they support a discussion of the pros and cons of screening between patients and their physicians.
Despite this, most men over 50 years old in the United States have had a prostate-specific antigen (PSA) test, in which the protein found in the prostate gland is measured through blood samples. And over the past 10 years, the number of prostate cancer-related deaths has decreased. The reason for the decrease, however, may not be increased screening, but improved methods of treatment.
Overdiagnosis leads to overtreatment
Screening methods for prostate cancer are somewhat imprecise. Abnormal results do not concretely mean cancer exists; the converse is true of normal results – most men with prostate cancer actually have “normal” PSA levels. This ambiguity can lead to overdiagnosis, which often translates into overtreatment – but aggressive treatment and the debilitating side effects that come with it, such as impotence or incontinence, may be unnecessary.
Donald Kaufman, MD
Prostate cancer is unique in its tendency to be slow-growing. Men are more likely to die of another cause before the cancer presents severe symptoms or becomes life-threatening. Many physicians are now recommending “active surveillance” in place of surgery or radiation, in which the cancer is regularly monitored for growth rather than treated directly.
“While we recognize that a PSA screening test is not in and of itself harmful and that a biopsy is reasonably safe, the real harm may take place if a positive biopsy leads to aggressive treatment of a limited, low-grade cancer never destined to become clinically significant,” says Donald Kaufman, MD, director of the Claire and John Bertucci Center for Genitourinary Cancers. About 30 percent of patients newly referred to the center are part of its active surveillance program.
Current studies hope to settle the prostate screening debate
Two ongoing studies in the medical community are attempting to settle the prostate cancer screening debate once and for all. The initial results of both were published in the March 18 edition of The New England Journal of Medicine. The first 11-year study of the National Cancer Institute included 76,693 men. Half of the men were assigned to 10 years of annual screenings; the other half were directed to continue receiving their usual health care without any specific recommendations. After 7 to 10 years of follow-up, the researchers concluded that the rate of prostate cancer-related death was “very low” and “did not differ significantly between the two study groups.”
Michael Barry, MD
The second set of results comes from a European trial of randomized prostate cancer screening in 162,342 men from seven European countries. The group who received screening was tested at an average of once every four years; the control group received no screening. The results demonstrated a 20 percent reduction in prostate cancer-related deaths in those who received PSA-based screening, but also showed a “high risk of overdiagnosis.” For every 10,000 men screened for 10 years, about seven fewer prostate cancer deaths would be expected. However, more than 300 more men would be diagnosed who would not have had to face a prostate cancer diagnosis without screening.
While the results suggest that routine prostate cancer screening does not significantly lower mortality rates – if it lowers them at all – no definitive conclusion can be drawn. The findings do demonstrate what physicians and medical organizations already believe: prostate cancer screening and treatment needs to be discussed between patients and physicians on a case-by-case basis.
Expert advice on prostate screening
“Serial PSA screening has at best a modest effect on prostate-cancer mortality during the first decade of follow-up. This benefit comes at the cost of the substantial overdiagnosis and overtreatment,” says Michael Barry, MD, of the Massachusetts General Hospital General Medicine Unit, in an editorial published as an accompaniment to the two studies. “A shared decision-making approach to PSA screening, as recommended by most guidelines, seems more appropriate than ever.”
“We advise a discussion between the physician and patient as to whether the patient desires screening,” says Kaufman. “We also emphasize that once a biopsy leads to a diagnosis of prostate cancer, that is a critical time for a full discussion between the physician and patient about a possible place for active surveillance in those who are most likely to benefit from the avoidance of aggressive treatment.”
In an age where medical diagnosis is increasingly in the hands of technologically advanced testing equipment, old-fashioned dialogue between patients and doctors remains as important as ever. Men ages 50 and older should talk to their physician about prostate cancer screening options; those at a greater risk for the disease due to family history or other factors should begin the discussion even earlier.
Learn more about the Mass General Cancer Center.
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