Why not screen such men? Experts point to the slow-growing nature of most prostate tumors, and the fast-shrinking lifespan of septuagenarians.
At age 75, "whether you have prostate cancer or not, most likely you'll die of something else," said University of Texas geriatrician Elizabeth Jaramillo, lead author of the JAMA study.
Even in younger men, studies have shown screening saves few if any lives, while treatment often causes urinary and sexual side effects. The problem is that no study can confidently say which cancers are trivial, and which are deadly.
The Texas researchers, who analyzed 1,963 primary-care physicians' PSA screening practices, found hundreds of those doctors tested the majority of patients over 75.
Jaramillo said many family physicians remained unaware that in the last five years, expert groups - including the American Urological Association, traditionally a fervent defender of the PSA test - had recommended that doctors discuss the pros and cons of screening with patients.
And for older patients, the cons outweigh the pros. Physicians "are not always taught to look at life expectancy," she said.
Old habits die hard, said a recent article in the Journal of Family Practice: "Physicians often opt to order a PSA test rather than take the time to explain the potential harms and benefits and listen to the patient's thoughts and feelings."
Nonetheless, Medicare and private insurers continue to rely on doctors' orders.
"If a man chooses to be screened with the advice of his doctor, Independence Blue Cross will cover one PSA screening test per year for men age 50 and older," Don Liss, the company's vice president of medical management, said by e-mail.
Said Jaramillo: "It seems pretty logical that not covering it would help cut down on overtesting rates."