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Canadian Study Shows Little Benefit of Mammography for Women Under 50 - 2002-09-06

Mammograms are an effective tool for detecting breast cancer in women, age 50 and older. But women in their 40's do not often get the disease. So doctors have been divided in recent years about the value of giving the breast x-ray screening test to younger women. Canadian researchers say that mammograms for women in their forties may do more harm than good.

The researchers say that when a woman has symptoms of breast cancer or her doctor suspects something, mammograms are enormously valuable. But their 10-year study of 50,000 women found that mammography screening does little to save the lives of women under 50. There were 105 deaths in the group that got mammograms versus 108 deaths among those that did not.

Cornelia Baines, a professor of public health at the University of Toronto and a co-investigator of the study says, "Now unfortunately, a lot of women will say when they hear me talking, 'Well, Dr. Baines, it can't do me any harm. I just want to go and get a mammogram. And then if I've got cancer, I'll know I've found it as early as possible. But if I don't have cancer, then I'm reassured and it won't do me any harm.' And they genuinely believe that. They do not know the potential harms that submitting to mammography may confer upon them."

For starters, Dr. Baines says there's something called a false negative mammogram.

"That is a mammogram that tells the lady you don't have cancer when she does," she said. "You may not realize it but mammography becomes increasingly less accurate the younger you are. And in women in their 40's, on average, mammography will miss one out of three breast cancers."

More significantly, because younger women have denser breast tissue than older women, what eventually prove to be harmless calcifications and other lumps tend to show up on their mammograms. This leads to a false positive rate that some experts find troubling, especially since it causes women to be put through a battery of nerve-wracking and uncomfortable tests, including biopsies, that turn out to be needless.

It's estimated that eight to ten percent of women ages 40 to 49 have an unnecessary biopsy as a result of a false positive mammogram.

Even some of the cancers in this younger age group that are detected do not need to be treated. That is the view of Dr. Steven Goodman, a professor of medicine at Johns Hopkins University in Baltimore, Maryland.

"There's no question that there's a certain number of tumors detected that would not progress [to cancer]," he said. "So what scientists and women have to confront is whether...the harm incurred of finding those and acting on them ..whether that harm is outweighed by the health benefit. As you get younger [the younger you are], it becomes a very, very close call."

U.S. experts recommend that women begin getting mammograms every one or two years beginning at age 40. The recommendation by the U.S. Preventive Services Task Force was made after it reviewed the results of eight randomized controlled studies, including preliminary data from the Canadian study.

Steven Woolf served on the task force. Dr. Woolf says while most of the studies show mammograms save lives in younger women, he concedes they have a difficult decision to make.

"I think it's conforting very often to be told with a fair amount of certainty this is something you should do or you should not do," he said. "But that's false comfort sometimes not to be told the full story. And medicine like everything else in life is a mixed bag and there are some benefits and some harms."

The results of the Canadian National Breast Cancer Screening Study, and summaries of the studies considered by the U.S. Preventive Services Task Force, are published in the journal Annals of Internal Medicine.