As chief medical and scientific officer of the American Cancer Society, Otis Webb Brawley -- who is also a professor of oncology and epidemiology at Emory University -- is the public face of the cancer establishment. He operates in a world of similarly high-achieving, multiple-credentialed, respectable professionals, where insults tend to be delivered, stiletto-style, in scientific language that lay people aren't meant to understand. So it can be more than a little jarring to hear, for example, James Mohler, chairman of the urology department and associate director of the Roswell Park Cancer Institute in Buffalo, say of his friend: ''I have known Otis for over 20 years. He doesn't come off as being ignorant or stupid, but when it comes to prostate-cancer screening, he must not be as intelligent as he seems.'' Or Skip Lockwood, the head of Zero, a prostate-cancer patient advocacy group, charge that Brawley is more concerned about saving men's sex lives than about saving the men themselves.

Brawley has become the target of these attacks because of his blunt and very public skepticism about the routine use of the prostate-specific antigen, or P.S.A., test to screen men for early prostate cancer. ''I'm not against prostate-cancer screening,'' Brawley says. ''I'm against lying to men. I'm against exaggerating the evidence to get men to get screened. We should tell people what we know, what we don't know and what we simply believe.''

The P.S.A. test, which was approved by the U.S. Food and Drug Administration in 1986, has become an annual ritual for millions of middle-aged men who assume that finding prostate cancer early will prevent death. By 2008, nearly half of men over 50 reported that they were screened in the previous 12 months. Despite the seeming logic of the P.S.A. test, the evidence that it saves lives is far from conclusive, and Brawley is not the only one questioning it. A growing cadre of doctors, epidemiologists, patients and cancer biologists are rethinking its value. And the most recent studies, while not ending the debate, indicate that routine P.S.A. testing appears not to reduce the number of deaths, and if it does, the benefit is exceedingly modest.

Patients and their doctors are now faced with radically polarized views about the logic of routine testing. On one side are physicians like Mohler, who argue that the test can reduce a man's chances of dying of prostate cancer, plain and simple. This side of the debate is passionate, backed by the persuasive conviction of men who have survived prostate cancer and well financed by the multibillion-dollar industry that has grown up around the testing and treatment of the disease.

The other camp makes a less emotionally satisfying argument: on balance, scientific studies do not support the claim that screening healthy men saves lives. Screening, Brawley and others argue, can lead healthy men into a cascade of further testing and treatments that end up injuring or even killing them. As Richard Ablin, who discovered a prostate-specific antigen, put it in an Op-Ed in The New York Times, using the P.S.A. test to screen for cancer has been ''a public health disaster.''

So what should a man do when his doctor suggests a routine P.S.A. test? The U.S. Preventive Services Task Force, a panel of independent experts that evaluates the latest scientific evidence on preventive tests and treatments, is charged with making recommendations in just such situations. It already recommends against routine screening for men over 75. According to an internal document, in 2009 the task force conducted an in-depth analysis of data and seemed poised to give routine P.S.A. testing a ''D'' rating -- ''D'' as in don't do it -- for any man of any age. But this was around the time that the task force stated that routine mammography for women ages 40 to 50 was not necessary for every woman. That recommendation caused a public uproar, and Ned Calonge, the task-force chairman at the time, sent the P.S.A. recommendation back for review. One year later, in November 2010, just before midterm elections, the task force was again set to review its recommendation when Calonge canceled the meeting. He says that word leaked out that if the November meeting was held, it could jeopardize the task force's financing. Kenneth Lin, the researcher who led the review, quit his job in protest, and now, nearly two years after its initial finding, it remains uncertain when the task force will release its rating for P.S.A. screening.

Cancer screening is a growing field; existing tests are becoming more sensitive, and new tests are constantly developed. We now have CT scanning for lung cancer, and there is also a blood test marketed by Johnson & Johnson known as a ''liquid biopsy,'' which searches for stray cancer cells in the bloodstream. More testing inevitably brings more treatment, because the urge to correct every cellular anomaly, no matter how small or potentially harmless, is practically irresistible. But if there is one lesson from the P.S.A. test, it is that more information and intervention do not always lead to less suffering.