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March 23, 2009
Results Question Annual Prostate Cancer Screening
The prostate-specific antigen (PSA) test can spot prostate cancer early. Surprisingly, annual tests might not lead to fewer prostate cancer deaths, according to a new report.
The prostate is a gland about the size of a walnut. Located just below the bladder, it produces fluid that makes up part of semen. Prostate cancer usually occurs in older men, and doctors often recommend that men 50 or older take the PSA test annually. Although there has been a drop in mortality from prostate cancer since the test has come into use, it hasn't been clear whether the PSA test has actually played a role in that drop.
The Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial is a 17-year project of NIH's National Cancer Institute (NCI) designed to provide answers about the effectiveness of certain cancer screening tests, including the PSA test. Of over 76,000 men, half were randomly assigned to annual screening with PSA tests for 6 rounds and digital rectal exams (DRE) for 4 rounds. In a DRE, a doctor manually feels for anything that's not normal. The men were referred to their usual health care provider for follow-up testing if their PSA level was greater than 4.0 nanograms per milliliter or if a DRE found an abnormality.
The other men were assigned to usual care, with no recommendations about prostate cancer screening. However, men in this group sometimes had the screening tests because of the growing public acceptance of them. Screening by PSA in this group increased from 40% at the beginning of the study to 52% up to a decade later. The use of DREs rose from 41% to 46%.
The first report from the trial appeared online on March 18, 2009, in the New England Journal of Medicine. After 7-10 years of follow-up, the rate of death from prostate cancer was very low and didn't differ significantly between the 2 groups. At 10 years, 17% more prostate cancers were diagnosed in the screening group (3,452, vs. 2,974 in the usual-care group). There were 92 prostate cancer deaths in the screening group, compared to 82 in the usual-care group. That difference isn't statistically significant. Follow-up of the PLCO participants will continue for several more years.
"What this report tells us is that there may be some men who are diagnosed with prostate cancer and have the side-effects of treatment, such as impotence and incontinence, with little chance of benefit," said NCI director Dr. John E. Niederhuber. "Clearly, we need a better way of detecting prostate cancer at its earliest stages and as importantly, a method of determining which tumors will progress."
Another report in the same journal, from a large European study, found that screening reduced prostate-cancer mortality by 7 deaths for every 10,000 men during 9 years of follow-up. That study design varied from the PLCO, and because the study is ongoing, the results are similarly not considered definitive. The European report also highlighted the risks of overdiagnosis and overtreatment. A whopping 23% of the screened men underwent biopsies, and about double the number of screened men had a radical prostatectomy or radiation therapy than those who were not screened.
NCI does not have a recommendation about prostate cancer screening. The U.S. Preventive Services Task Force recently concluded there was wasn't enough evidence about its benefits and harms to make a recommendation for men younger than 75. For men 75 and older, they recommend against screening. Their assessment, however, was done before the new reports came out. Given the uncertainties, NCI continues to pursue many avenues to find new ways of screening for prostate cancer.