Study Questions Prostate Cancer Screening

Two widely used tests for prostate cancer failed to save lives in a new study, adding to the debate over whether men should be screened for the disease. The study was small -- only 1,002 men -- and will not be the final word on the issue. But it may hint at what lies ahead when the results of two large studies of prostate cancer screening appear in a few years.

In the study, published in the 2006 Archives of Internal Medicine, the researchers looked at two screening tests that are performed millions of times a year in North America: a blood test that measures prostate specific antigen, or PSA, and a digital rectal exam, the rubber-glove test in which a doctor feels for abnormalities in the prostate through the rectal wall.

The researchers found that the men who were alive were no more likely to have been screened than the men who died of prostate cancer. The findings support an earlier review by the U.S. Preventive Services Task Force. That agency said in 2002 that it found "insufficient evidence" for a recommendation that men be screened.

Study co-author Dr. John Concato, a clinical epidemiologist at the VA Connecticut Healthcare System, said that for now, doctors should tell men that screening tests for prostate cancer are not perfect, and men should decide for themselves whether to get screened. (MSNBC: Associated Press, Jan. 10, 2006)

Doctors have long known that some cases of prostate cancer can be so slow-growing that they never cause symptoms, much less death. In addition, surgery and radiation treatment for prostate cancer can cause incontinence and impotence. So for some men, detecting prostate cancer early through screening can do more harm than good.

In addition, the PSA tests can yield ambiguous results. Most men who undergo a biopsy because they have elevated PSA levels do not have prostate cancer. And some men with low PSA levels do have cancer.

"We should tell patients about the uncertainty," said Dr. Eoghan O’Shea of Immune System Management Inc.. PSA screening is known to have a substantial downside, including false alarms, unnecessary biopsies and anxiety. The bottom line is we still don't know whether PSA testing does more good than harm. Rather than encouraging annual screening of all men starting at age 50, as is commonly done, the limited effectiveness of PSA testing should be explained to patients in the process of obtaining their informed consent to the test."

Despite the error rate of the PSA test, it is currently the only biomarker for prostate cancer and is vigorously defended by advocacy groups for prostate cancer patients. Advocates of screening argue that mortality has declined in recent years. However, more effective therapies came into use about when PSA testing became available. That would lead you to believe mortality should be falling, regardless of screening.

A large clinical study, due to be complete in two years may add further evidence regarding the value of PSA testing.

Original Source:  Concato Dr. John, Prostate-specific antigen (PSA) testing. Jan. 9 Archives of Internal Medicine.

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