Fewer men are being screened for prostate cancer, and fewer early-stage cases are being detected, according to two studies published Tuesday in The Journal of the American Medical Association.

The number of cases has dropped not because the disease is becoming less common but because there is less effort to find it, the researchers said.

The declines in both screening and incidence “could have significant public health implications,” the authors of one of the studies wrote, but they added that it was too soon to tell whether the changes would affect death rates from the disease.

Because prostate cancer often grows slowly, the panel said, screening finds many tumors that might never have harmed the patient. But they are treated anyway. As a result, it concluded, testing saves few lives and leads too many men into unneeded surgery or radiation, which often leaves them impotent and incontinent.

An editorial accompanying the articles, by Dr. David F. Penson, the chairman of urologic surgery at Vanderbilt University Medical Center, acknowledged that too much screening could do harm but suggested that the pendulum had swung too far the other way.

Rather than issuing a blanket recommendation against screening, Dr. Penson said, it would be better to “screen smarter” by testing most men less often and focusing more on those at high risk.

One of the new studies, by researchers from the American Cancer Society, found that early-stage diagnoses of prostate cancer per 100,000 men age 50 and older dropped to 416.2 in 2012, from 540.8 cases in 2008, with the biggest decrease occurring from 2011 to 2012 - after a draft of the task force guidelines was released in October 2011. The authors estimated that the total number of diagnoses decreased to 180,043 in 2012 from 213,562 in 2011 - a difference of 33,519 cases.

That difference may indicate that many men were spared needless treatment - exactly what the task force had hoped to accomplish with its guidelines. But the authors also said, “Less screening or discontinuing screening may lead to missed opportunities for detecting biologically important lesions at an early stage and preventing deaths from prostate cancer.”

The percentage of men 50 and older who reported PSA screening in the previous 12 months dropped to 30.8 percent in 2013, from 37.8 percent in 2010.

Although the study could not prove that the drop in screening caused the drop in diagnoses, the authors said it was the most plausible explanation.

The findings were based on data from cancer registries and national surveys that asked men about prostate screening.

A second study, by researchers from several medical centers, also found a significant decline in PSA testing after the 2012 task force recommendations.

“With PSA testing, we often detect cancers that don’t need to be treated - clinically indolent, meaningless cancers,” Dr. Penson said in an interview. “It is true that more men die with prostate cancer than of it.”

He said the recognition that many prostate cancers were indolent, or slow-growing, and not deadly had led to major changes in medical practice, making doctors less inclined to automatically operate if cancer is found.

The cancer society recommends that men discuss screening with their doctors to decide whether they should have it.

Some men, told the pros and cons, decide against having any screening. Others opt for the testing, and if cancer is found, want it removed even though it might not be deadly.

But some who choose to be tested prefer another approach if cancer is found: “active surveillance,” which may involve repeated PSA tests and a biopsy every other year to find out if the cancer is growing and becoming more aggressive.

Dr. James A. Eastham, the chief of the urology service at Memorial Sloan Kettering Cancer Center in New York, said two long-term studies had shown that this type of monitoring was a reasonable way to determine which patients needed treatment. Most patients considered low-risk turned out to have very low rates of cancer progression.

“Some do go on to treatment eventually, but the majority do not die of prostate cancer,” Dr. Eastham said. About 2 percent do die from the disease, he added. And he said that even with the best possible active surveillance, some patients will still be overtreated.

Dr. Penson said that when active surveillance is explained, “of course men look and say, ‘That would be great if I can avoid having surgery or radiation.’ ”

“ ‘If you think this cancer is not a problem, Doc, I’ll take that every day and Sunday.’ It’s not hard to convince patients,” Dr. Penson added.

Dr. Eastham and Dr. Penson said there had been two extremes in testing, neither satisfactory. First, doctors screened all men over 50 with PSA tests and operated on all cancers. But now they may be heading toward the other extreme of not screening anybody.

Both doctors said that screening should be based on a man’s preferences and individual risk, and that better ways to screen were needed, methods that would let doctors zero in on the cancers that needed to be treated and could be cured. Promising new imaging techniques and blood tests for biomarkers that would reveal cancer are in the works, they said.

“But they’re not ready for prime time, so we’re stuck with the hand we’ve been dealt, the PSA test, which is an imperfect test,” Dr. Penson said. “But we can do a better job with it.”

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By DENISE GRADYNOV