The Verdict's Still Out
Are mammograms lifesavers or a waste of time? An independent panel of cancer experts has again raised doubts about the X-rays, announcing on Wednesday that there was insufficient evidence to show that they prevented women from dying from breast cancer. The group, the P.D.Q. screening and prevention editorial board, found flaws in seven major studies indicating that mammograms could prevent breast-cancer deaths in women over 40. NEWSWEEK science writer and Senior Editor Sharon Begley assesses the possible impact of the panel's findings:
What are the implications of the panel's statements? Are the members saying that early detection is unnecessary?
Sharon Begley: Oncologists have found time and again that the earlier breast cancer is detected, the more likely is the woman to survive the disease. How, then, can mammograms not save lives? Let's be clear what the National Cancer Institute's expert panel concluded: that there is no incontrovertible evidence that mammograms prevent breast-cancer deaths. We have been down this road before: in 1997 an expert panel of the National Institutes of Health voted not to recommend regular mammograms for women in their 40s. The panel concluded: "breast cancer mortality is no lower in women who [received mammograms in their 40s] than in controls." But then, the value of mammograms for older women seemed clear. Now even that is out the window.
How can this square with the finding that early detection is key to survival? Let's take younger women first. In women 40 to 49, breast cancer is rare: 16 cases per 1,000 women. Since relatively few die of the disease in the first place, it would take an awfully powerful detection technique, not to mention effective treatment, to make much of a statistical dent in the death rate. And mammography in younger women isn't that accurate, partly because it does not see well through their dense breast tissue. According to the NCI panel, mammograms miss as many as 25 percent of invasive cancers in 40- to 49-year-old women. What about older women, whose less-dense breast tissue is more amenable to mammograms? Let's say a woman has a slow-growing, "indolent" tumor. With or without mammography, those are usually curable, typically by lumpectomy. So women skipping regular mammograms would have just as high a survival rate as women who have them. Indolent tumors might make up half of all breast tumors. But if a tumor is aggressive, even by the time a mammogram finds it, a few cells will have likely broken off to seed another organ with cancer. In other words, early detection may still be too late. A 1996 study found that women in their 40s had much faster-growing tumors than older women, possibly because cancer-causing genes kick in at a younger age or because higher levels of estrogen feed these tumors. So in both indolent and aggressive cancers, mammograms make little difference. That's why their benefits are not showing up in studies, and that's why the NCI panel concluded that evidence of their benefits is lacking.
Does this mean insurance companies are now likely to cut back on paying for mammograms?
That's very unlikely. The final verdict on mammograms is not in, so as long as there is a chance that they save lives-and remember, what the panels concluded this week as well as in 1997 is that the benefit is not proved--insurers will almost certainly continue to cover them. Insurers did refuse to cover bone-marrow transplant costs for women with breast cancer, but in that case they were right: the procedure did not extend life or health.
Does this finding only apply to women in their 40s?
The 1997 analysis cast doubt on the value of mammograms for younger women--that is, those under 50. The current panel has extended those doubts to older women.
It's obvious why insurers and researchers are concerned about this issue. But for an individual woman, what's the downside of having an unnecessary X-ray?
This is a key point: The radiation dose in a mammogram is so low that it poses virtually no risk of triggering a cancer in healthy cells. "Virtually" because there is a small percentage of women who carry a genetic mutation that makes them supersensitive to radiation. The greater risk is of false positives-that is, detecting something that is not cancer. Another crucial consideration is whether a woman and her doctor understand the limitations of mammograms. Even having an annual screening doesn't mean a woman can skip monthly self-examination of her breasts. A clean mammogram does not mean a woman is cancer-free.
Given all this conflicting information, what should women do now?
The National Cancer Institute has not changed its recommendation that women have regular mammograms, starting in their 40s. Even researchers who cast doubt on whether mammograms save lives agree that there is little harm in having them as recommended by a woman's doctor, as long as the women understands their limitations and the danger of false positives. The bottom line is clear if not pretty: you can't count only on mammograms.