Now expert groups are proposing less screening for prostate, breast and cervical cancer and have emphasized that screening comes with harms as well as benefits.
Two years ago, the influential United States Preventive Services Task Force, which evaluates evidence and publishes screening guidelines, said that women in their 40s do not appear to benefit frommammograms and that women ages 50 to 74 should consider having them every two years instead of every year.
This year the group said the widely used P.S.A. screening test for prostate cancer does not save lives and causes enormous harm. It also concluded that most women should have Pap tests for cervical cancer every three years instead of every year.
What changed?
The answer, for the most part, is that more information became available. New clinical trials were completed, as were analyses of other sorts of medical data. Researchers studied the risks and costs of screening more rigorously than ever before.
Two recent clinical trials of prostate cancer screening cast doubt on whether many lives — or any — are saved. And it said that screening often leads to what can be disabling treatments for men whose cancer otherwise would never have harmed them.
A new analysis of mammography concluded that while mammograms find cancer in 138,000 women each year, as many as 120,000 to 134,000 of those women either have cancers that are already lethal or have cancers that grow so slowly they do not need to be treated.
Cancer experts say they cannot ignore a snowballing body of evidence over the past 10 years showing over and over that while early detection through widespread screening can help in some cases, those cases are small in number for most cancers. At the same time, the studies are more clearly defining screening's harms.
"Screening is always a double-edged sword," said Dr. Otis Brawley, the chief medical officer of the American Cancer Society. "We need to be more cautious in our advocacy of these screening tests."
But these concepts are difficult for many to swallow. Specialists like urologists, radiologists and oncologists, who see patients who are sick and dying from cancer, often resist the idea of doing less screening. General practitioners, who may agree with the new guidelines, worry about getting involved in long conversations with patients trying to explain why they might reconsider having a mammogram every year or a P.S.A. test at all.
Some doctors fear lawsuits if they do not screen and a patient develops a fatal cancer. Patients often say they will take their chances with screening's harms if a test can save their lives.
And comments like Dr. Brawley's give rise to other questions as well. Is all this happening now because of worries over costs? And in any case, is all this simply an academic argument, since most doctors, faced with real patients, still suggest frequent screening and their patients agree?
The answer, cancer experts say, is, to a certain extent, all of the above. But, they say, there does seem to be a change in the air. Researchers used to be afraid to even broach the subject of screening's harms.
"It was the third rail," said Dr. H. Gilbert Welch of Dartmouth Medical School. "We were afraid to say exactly what we thought for fear of seeming too crazy." It was easy to get financing to study the benefits of screening, he added, but a study that looked at harms was "too far out of the culture."
Not now, he said.
And with that change has come a new look at screening.
"No longer is it just, Can you find the cancer?" Dr. Brawley said. "Now it is, Can you find the cancer, and does finding the cancer lead to a decrease in the mortality rate?"
Then there is the new emphasis on cost.
The current issue of The New England Journal of Medicine, for example, has an article by two prostate cancer specialists who note that one recent study concludes that $5.2 million must be spent on screening to prevent one prostate cancer death. And, add the authors, Dr. Allan S. Brett of the University of South Carolina School of Medicine and Richard J. Ablin of the University of Arizona, that figure is not inclusive. The true cost is undoubtedly even greater.
"We believe that the current P.S.A.-based screening paradigm does not compare favorably with competing health care priorities," they wrote.
The cost of screening, said Dr. Russell P. Harris, a screening researcher at the University of North Carolina, "is one of the factors that is pushing toward a tipping point."
But, medical experts note, many people, including doctors, are confused by the changing message, which is understandable.
"You don't turn decades of thought around immediately," said Dr. Timothy J. Wilt, a task force member from the University of Minnesota.
In part, doctors and patients are stuck in a sort of cancer time warp. The disease was defined in 1845 by a German doctor, Rudolf Virchow, who looked at tumors taken at autopsy and said cancer is an uncontrolled growth that spreads and kills. But, of course, he was looking only at cancers that killed. He never saw the others.
"Now we are backing away from that," Dr. Brawley said. In recent years, researchers have found that many, if not most, cancers are indolent. They grow very slowly or stop growing altogether. Some even regress and do not need to be treated — they are harmless.
"We are going from an 1845 definition of cancer to a 21st-century definition of cancer," Dr. Brawley said.
Dr. Brawley, too, noticed that more people are starting to understand the limitations of screening, and its risks.
Change, though, has been slow in the face of intense promotion of screening by medical practices, hospitals and advocacy groups and years of misunderstandings about screening's benefits and risks.
"You've got all this positive stuff" about screening, Dr. Brawley said. "And you have been taught since you were on your mother's knee that the way to deal with cancer is to find it early and to cut it out."
Yet he is optimistic.
"I think people are actually starting to understand that we need to be a little more rigorous in what we accept about screening," Dr. Brawley said. "I do sense there is some movement there."
