Earlier this month, a major study caused international headlines when it found that mammograms do not reduce mortality from breast cancer in women between 40 and 59 years old. The study, published by the BMJ (formerly known as the British Medical Journal), followed almost 90,000 women in Canada for 25 years; the women had been randomized to receive either mammograms plus breast exams, or breast exams alone.
The death rate was comparable in both groups. The researchers also reported that one-fifth of the tumors detected among women getting the mammograms were “over-diagnosed”—that is, they were not likely to lead to death even if they had not been treated.
This study is just the latest to weigh in on the benefits—or lack of benefits—attributable to mammograms, and its findings might lead to even more confusion among women about whether or not they should undergo such screening. To understand the implications of the study, I interviewed Robert Hiatt, M.D., Ph.D., a professor of epidemiology and biostatistics at the University of California, San Francisco (UCSF) and associate director of the UCSF Comprehensive Cancer Center.
What is the main message of the study?
Dr. Robert Hiatt: This study is from a pretty careful and well-respected group of researchers. It re-ignites a very long debate about the value of mammography, and adds to an increasingly skeptical view of the value of mammography as we have long thought of it in this country. In this case, the comparison group was one in which the women had clinical breast exams—pretty good clinical breast exams, because the examiners were well-trained. Essentially what they’re saying is, you’re not going to see much benefit from mammograms in an advanced country where you’ve got the capacity to track women through high-quality clinical breast exams on a regular basis, and where effective treatment is available if something is detected early enough.
What doesn’t the study tell us?
RH: This is a population-based study that treated all women as if equally at risk. It didn’t look at the possible benefit of mammograms for women at different levels of risk. Breast cancer behaves differently in some women than others—women with certain genetic markers are at higher risk, as are women with greater breast density and those of increasing age. Women at higher risk are more likely to develop cancers, period, and are also more likely to benefit from screening because of the rapidity of the development of those cancers. This study didn’t look at that at all.
If mammograms aren’t effective, why do so many women believe the technology saved their lives?
RH: When a woman is screened and something is found and treated successfully, it is natural for her to do quite well and attribute her good fortune to the screening—the action step under her or her doctor’s control. However, that very same woman could have had a good outcome without the screening if the tumor was not going to progress, or if it was a small lump found early enough for curative therapy. It is hard to tell someone that she didn’t really need the screening or the surgery that followed, and we as clinicians usually can’t predict which tumors will progress and which won’t. That is the holy grail of screening research—to be able to differentiate between dangerous tumors and benign tumors that are detected early.
What do these findings mean for a woman deciding whether or not to cancel an upcoming mammogram appointment?
RH: I think individual women should continue on whatever regimen they have—the one that's been recommended by their doctors. Over the last 20 or 30 years this question of the value of mammograms has come up frequently, and I’m afraid women have been whipsawed by conflicting advice. So before jumping to another posture, I think I would let this study be evaluated against other data and see what expert opinion emerges after those reviews.