Prostate Exams: When Are They Necessary?

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Howard Sochurek / Corbis

A thermograph of prostate cancer

Science is not shy about ambiguity, never more so than when it comes to medical advice. So here's the latest recommendation on prostate-cancer screening: Men should continue to have both a manual prostate exam and a blood test for prostate-specific antigen (PSA) every year — bearing in mind that neither test may affect your odds of surviving prostate cancer. (Read "Can a Urine Test Detect Deadly Prostate Cancer?")

Those seemingly contradictory conclusions are part of the results of the Prostate, Lung, Colorectal and Ovarian Cancer Screening trial (PLCO), a sweeping, 17-year project conducted by the National Cancer Institute (NCI). The prostate findings were published online on March 18 in the New England Journal of Medicine, and while they may leave many men scratching their head, they do offer some valuable information about the benefit of screening. (Read "Vitamins Do Not Prevent Prostate Cancer, Study Finds.")

The prostate portion of the study looked at a sample group of nearly 77,000 men in 10 health-care centers across the U.S. Half the men were randomly assigned to receive regular PSA tests and physical exams. Since investigators could not ethically recommend that the other group not receive the screenings — which are, for now, considered the first defense against prostate cancer — they were simply given no particular recommendation at all. Half that group went ahead and had the exams on their own, and the remaining men did not.

The results confirmed the value of annual screening in detecting cancer. After seven years, 2,820 cases of cancer were caught in the group that had been instructed to have annual checkups, vs. 2,322 in the group that was left on its own — a difference of 22%. The reasonable conclusion is not that the second group just happened to be healthier but that a significant share of their cancers went undetected. So case closed, right?

Not necessarily — at least not when you consider mortality. At the end of the seven years, 50 men in the screening group had died of prostate cancer, compared with 44 in the other group; at the end of 10 years, those numbers were 92 to 82. There were actually more deaths in the screening group, but the differences were too small to be statistically significant; in other words, it was a wash.

"When we find prostate cancer," says Dr. Gerald Andriole of Washington University in St. Louis, Mo., who participated in the study, "we don't know if it's a killer or a toothless lion — the kind of cancer men will die with, not of."

But shouldn't doctors attack any cancer aggressively? Usually, but in the case of the prostate, things are less clear. Many cases of prostate cancer are very slow-growing, so slow that, depending on a man's age and overall health, he may die of something else before the cancer can ever hurt him. Meanwhile, aggressive treatments, particularly surgery, can lead to impotence or incontinence or both — a high price to pay for a disease that was not going to trouble you much.

"There are men who have the side effects of treatment who would never have died or suffered those ill effects," says lead author Dr. Chris Berg, of the NCI.

The question for any man with a positive PSA test or manual exam is, Which group does he belong to? The NCI admits that screening tests alone cannot determine which tumors are deadly, and researchers won't know until they follow the study's entire sample group to see how all the men fare well beyond the seven- or 10-year point — which is their plan. Perhaps some whose cancer was not a problem at the decade mark will be claimed by the disease five or 10 years later. "We need longer follow-ups to determine if more screening will translate to fewer deaths," says Berg.

Just as important, science is working to develop tests that are more precise than the fallible feel method or even the PSA reading. Ideally, once a blood test reveals elevated antigens, it could also spot particular markers for cancers that are aggressive enough to be deadly and distinguish them from markers for cancers that are tamer.

"Looking at the advances in genetic profiling," says Andriole, "I think this kind of advance is just around the corner. But is it two years, five years? We're not sure."

For now, Andriole recommends a screening approach tailored to the particular patient. "If the man sitting in front of me was an elderly man with a medical condition and he looked like he had a limited life expectancy — say seven to 10 years," Andriole says, "I think I could have a good conscience in telling him that the PSA test is not necessarily for him."

For men with more time left, the smart approach is probably to stick with the exams. A positive test may mean a biopsy, and those results will determine the need for treatment. It's not precise, but it is science — and for now, that's the best we've got.

Read "The Year in Medicine 2008: From A to Z."