Vast Study Casts Doubts on Value of Mammograms

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One of the largest and most meticulous studies of mammography ever done, involving 90,000 women and lasting a quarter-century, has added powerful new doubts about the value of the screening test for women of any age.

It found that the death rates from breast cancer and from all causes were the same in women who got mammograms and those who did not. And the screening had harms: One in five cancers found with mammography and treated was not a threat to the woman’s health and did not need treatment such as chemotherapy, surgery or radiation.

The study, published Tuesday in The British Medical Journal, is one of the few rigorous evaluations of mammograms conducted in the modern era of more effective breast cancer treatments. It randomly assigned Canadian women to have regular mammograms and breast exams by trained nurses or to have breast exams alone.

“It will make women uncomfortable, and they should be uncomfortable,” said Dr. Russell P. Harris, a screening expert and professor of medicine at the University of North Carolina, Chapel Hill, who was not involved in the study. “The decision to have a mammogram should not be a slam dunk.”

The findings will not lead to any immediate change in guidelines for mammography, and many advocates and experts will almost certainly dispute the idea that mammograms are on balance useless, or even harmful.

Dr. Richard C. Wender, chief of cancer control for the American Cancer Society, said the society had convened an expert panel that was reviewing all studies on mammography, including the Canadian one, and would issue revised guidelines later this year. He added that combined data from clinical trials of mammography showed it reduces the death rate from breast cancer by at least 15 percent for women in their 40s and by at least 20 percent for older women.

That means that one woman in 1,000 who starts screening in her 40s, two who start in their 50s and three who start in their 60s will avoid a breast cancer death, Dr. Harris said.

“It might be possible that mammography screening would work if you don’t have any awareness of the disease,” she said.

The Canadian study reached the same conclusion about the lack of a benefit from mammograms after 11 to 16 years of follow-up, but some experts predicted that as time went on the advantages would emerge.

That did not happen, but with more time the researchers could, for the first time, calculate the extent of overdiagnosis, finding cancers that would never have killed the women but that led to treatments that included surgery, chemotherapy and radiation.

Many cancers, researchers now recognize, grow slowly, or not at all, and do not require treatment. Some cancers even shrink or disappear on their own. But once cancer is detected, it is impossible to know if it is dangerous, so doctors treat them all.

Mammography’s benefits have long been debated, but no nations except Switzerland have suggested the screening be halted. In a recent report, the Swiss Medical Board, an expert panel established by regional ministers of public health, advised that no new mammography programs be started in that country and that those in existence have a limited, though unspecified, duration. Ten of 26 Swiss cantons, or districts, have regular mammography screening programs.

Dr. Peter Juni, a member of the Swiss Medical Board until recently, said one concern was that mammography was not reducing the overall death rate from the disease, but increasing overdiagnosis and leading to false positives and needless biopsies.

“The mammography story is just not such an easy story,” said Dr. Juni, a clinical epidemiologist at the University of Bern.

Even experts like Dr. H. Gilbert Welch, a professor of medicine at Dartmouth, who have questioned mammography’s benefits were surprised by Switzerland’s steps to reconsider its widespread use.

“Wow, times they are a-changin’,” Dr. Welch said.

In the United States, about 37 million mammograms are performed annually at a cost of about $100 per mammogram. Nearly three-quarters of women age 40 and over say they had a mammogram in the past year. More than 90 percent of women ages 50 to 69 in several European countries have had at least one mammogram.

Dr. Kalager, whose editorial accompanying the study was titled “Too Much Mammography,” compared mammography to prostate-specific antigen screening for prostate cancer, using data from pooled analyses of clinical trials. It turned out that the two screening tests were almost identical in their overdiagnosis rate and had almost the same slight reduction in breast or prostate deaths.

“I was very surprised,” Dr. Kalager said. She had assumed that the evidence for mammography must be stronger since most countries support mammography screening and most discourage PSA screening.

Source: New York Times. Click here for the original article.