The debate about screening older men for prostate cancer was reignited last week after reports that the billionaire investor Warren Buffett, who is 81, said he received a diagnosis of early-stage prostate cancer after a routine blood test for prostate specific antigen, or P.S.A.
In 2008, the United States Preventive Services Task Force recommended that men 75 and older no longer be given a routine P.S.A. test. The test is notoriously unreliable in older men, who often have elevated P.S.A. scores as a result of natural aging or an enlarged prostate. And even when cancer is found as a result of a P.S.A. test in older men, it typically is so slow-growing that it will never cause harm.
Continued testing of men 75 and older, the task force concluded, was far more likely to result in significant harm, including unnecessary treatment that could cause pain, incontinence and impotence, among other risks.
But very few men and their doctors have heeded the task force advice, according to new research published in The Journal of the American Medical Association.
Researchers from the University of Chicago and the University of California, Los Angeles, studied data collected from the National Health Interview Survey, which every five years includes 13 questions about P.S.A. testing. Among the 5,332 men surveyed in 2005 and the 4,640 men queried in 2010, two years after the new guidelines were issued, the researchers found no difference in the rate of P.S.A. testing among older men. In both cohorts, about 43 percent of men 75 or older were being screened.
In fact, in 2010, P.S.A. screening was more common in men 75 or older than in men in their 40s and 50s. Experts continue to debate the relative benefits of P.S.A. testing at all ages, but most agree that younger men may have the most to gain from screening.
"To our disturbing surprise, the men most likely to benefit were being screened at about half the rate of men in their 70s or 80s, who are the men least likely to benefit," said Dr. Scott Eggener, co-director of the urological oncology fellowship program at the University of Chicago Medical Center and senior author of the study.
Not every medical group opposes P.S.A. testing of older men. The American Cancer Society and the American Urological Association discourage screening for men whose life expectancy is 10 years or less, but suggest that a man who is expected to live 10 years or longer discuss the risks and benefits of testing with his doctor.
Mr. Buffett has disclosed that he will undergo radiation treatment for the cancer, but he has not shared further details that would illuminate his risk, such as the Gleason score indicating how aggressive the cancer may be. Although his life expectancy, based on actuarial data, is an additional seven to eight years, he appears to be in robust health, and his doctors may feel that a life expectancy of 10 years or more is a strong possibility based on his health and family history.
However, many older men have health problems, such as diabetes or heart disease, that would shorten their life expectancy, and most experts agree they should not be tested.
Dr. Otis Webb Brawley, chief medical officer for the American Cancer Society, said that many doctors continue to test anyway, because they don't want to have a conversation with their patients about life expectancy.
"If you decide not to do the P.S.A., then you've got to have this conversation you really don't want to have with the patient," Dr. Brawley said. "For doctors to do that, it is emotionally challenging. Talking to someone else about their mortality is really uncomfortable for doctors."