Sept. 3, 2002 -- It's not a question of whether women should get regular mammograms. Experts disagree on when they should start. And the latest study showing that women in their 40s are just as likely to die of breast cancer whether or not they get mammograms only further ignites the debate.
Nearly everyone agrees that women aged 50-69 should have regular mammograms. But what about women in their 40s? The U.S. Preventive Services Task Force (USPSTF) now advises women aged 40-49 to get mammograms, but notes that the benefit is small.
Small indeed, according to a new USPSTF report in the Sept. 3 issue of the Annals of Internal Medicine. The report reviews all clinical trials of mammograms. To keep one woman younger than 50 from dying of breast cancer, the report says, it's necessary to screen almost 1,800 women for 14 years.
"Over time, mammography is almost as effective in younger women as in older women," lead researcher Linda L. Humphrey, MD, MPH, says. "The benefits are quite modest." Humphrey is associate professor of medicine at Oregon Health Sciences University and director of the Women's Health Fellowship Program at the Portland Veterans Affairs Medical Center.
There may not even be that much of a benefit, according to another study in the same issue of the Annals. The Canadian National Breast Screening study is a clinical trial in which more than 50,000 women aged 40-49 received either annual mammograms or training in self-examination with free medical follow-up. Earlier results from this trial showed that the women who got mammograms actually had more breast-cancer deaths. The latest data shows that after 11-16 years, those who got mammograms did no better than those who did not.
"What our study shows is that mammography detects more cancers. Mammography detects smaller cancers. Mammography detects cancers with less spread to the lymph nodes. Yet if you compare women aged 40-49 who got this screening with women who did not, the number of breast-cancer deaths after 13 years is precisely the same," study researcher Cornelia J. Baines, MD, tells WebMD. Baines is professor emerita at the University of Toronto.
"Despite the best intentions, some studies have such serious flaws that their findings simply do not reflect the underlying truth," Smith says in a statement. "The goal of screening is to reduce the incidence rate of advanced disease, so that treatment begins earlier. The Canadian investigators failed to accomplish this, so we see no difference in their death rates."
A study recently co-authored by Smith compared the medical records of Swedish women who actually got mammograms with those of women who did not. It found a 45% reduction in breast cancer in the screened women.
The leader of the Canadian study, Anthony B. Miller, MD, dismisses these findings.
"That Swedish population study was terrible," Miller tells WebMD. "It has all the biases of historical comparisons. It was not randomized, they over-interpreted their data, they cannot from their data determine how much of the reduction in cancer deaths was due to better treatments and how much was due to mammography. Yet, they say the benefit was largely due to mammography."
An editorial by Steven Goodman, MD, PhD, MHS, of Johns Hopkins Sidney Kimmel Cancer Center, Baltimore, accompanies the Canadian and USPSTF studies.
"It is wrong to look at the Canadian study as a line in the sand," Goodman tells WebMD. "It does not say there is no effect from mammography in women aged 40-49. It says there is a range of possible effects, and this is closer to zero than other studies. All the clinical studies of mammography are similar -- they overlap in the region of very modest benefit."
Whatever the benefit of mammograms in 40-something women, Goodman warns that it must be weighed against the risks. The main risk is a false-positive finding -- that is, a mammogram that says a biopsy is needed when there turns out to be nothing wrong. Such findings lead to biopsies, lumpectomies, and even mastectomies. They also cause a great deal of anxiety.
"The chance of a false-positive mammogram and subsequent biopsy is 40-50% if you have 10 mammograms," Goodman says. "And the benefit is extremely small if it exists at all. For a woman in her 40s, the risk of dying from breast cancer is only 1 in 350-400. The benefit is on the order of 1 in 2000 -- one of the smallest benefits known to medicine."
What Should Women Do?
WebMD asked each of the breast-cancer experts cited above what they would tell a woman in her 40s to do about breast-cancer screening. Their replies:
Humphrey: "I practice medicine. My own belief is that mammography probably is effective and better than nothing -- but it has risks. It is really important to discuss the risks with women. I tend to recommend it in my practice: mammograms every one to two years. I recommend more frequent mammograms in younger women than in older women, as cancers may be faster growing in younger women."
Goodman: "I do not have a clinical practice, so it's far too easy for me to say what to do from my ivory tower. But my wife and our friends are exactly in that age group. Most of them, not all, are choosing not to have mammograms because they understand that negative consequences are quite probable. It is such a close call with real issues on both sides of the scale. I would never, ever say to someone, 'You should do or not do this.' I would say, 'These are the positives, these are the negatives, you decide. There are real harms and real benefits that come very close to even."
Smith: "This does not change the American Cancer Society's position on mammography." That position: Women age 40 and older should have a screening mammogram every year.
Miller: "We are not telling women to do nothing. We are telling women to do quite a lot. Women must be trained to perform self exams and, if they are worried, to see their doctors."
Baines: "What I tell women is to be aware of their breasts. We should look for changes and for [differences] compared to the last time we looked. It doesn't require breast self-examination to do this. It is a question of looking in the mirror and saying, 'Hey, one round part of my breast isn't as round,' or 'One part is thicker than before.' Then go to your doctor and insist on a diagnostic mammogram. I know all this is difficult. We need a better tool for early detection."