Does screening mammography save lives?

Related article: Which women are most likely to die from breast cancer—those screened annually starting at age 40, biennially starting at age 50, or not at all? Mark D. Pearlman, MD (Examining the Evidence, November 2013)

James Dickinson, MBBS, PhD, a family physician and member of the Canadian Task Force on Preventive Health Care (a forerunner of the USPSTF), which has published its own set of guidelines on breast cancer screening, has a different perspective. Dr. Dickinson teaches at the University of Calgary in Alberta.

“One of the tendencies—particularly in medicine driven by commercial interests—is that as soon as there is even the slightest hint that something is worthwhile, there’s a rush to have everybody do it and make lots of profit from it. People don’t wait for the evidence. They jump to assume guilt or innocence without even looking for the evidence.”

“I give all credit to the Canadian trial investigators,” Dr. Dickinson says. “The world had jumped ahead of them and just assumed that breast screening worked. But they kept looking. They set up a good trial to start with and then followed it through and helped us understand that things aren’t as good as we would like them to be.”

Andrew M. Kaunitz, MD, professor and vice chair of obstetrics and gynecology at the University of Florida–Jacksonville also believes that the Canadian study’s findings are reliable. Dr. Kaunitz serves on the OBG Management Board of Editors.

“As pointed out in an editorial accompanying the Canadian trial, this study’s findings of a lack of efficacy of screening mammograms are ‘strikingly similar’ to other recent studies assessing breast cancer screening.”^9–11

“Further, mammograms are costly and associated with a high rate of false-positive findings,” Dr. Kaunitz says.

“Too many weak links”
Among the main criticisms of the Canadian trial is a claim of flawed methodology.

“The Canadian trial is an update of a flawed study that was previously discredited for good reasons,” says Dr. Monsees. “In short, the quality of the mammograms was poor, and the overall study design did not reflect a true randomization process.”

“For example, true randomization requires eligible patients to be randomly divided into two or more groups, without any knowledge of their specific conditions that might bias trial results,” Dr. Monsees explains. “In the most valid randomized trials, this was accomplished by invitation. Without knowing anything about the women, investigators randomly assigned them to a group invited to be screened and a group not invited. In this manner, two equal groups were produced, with no way to corrupt the randomization process.”

“In the Canadian National Breast Screening Study, in contrast, once the ­women volunteered, they were given a clinical breast examination, and women with breast lumps and large lymph nodes in their underarms were identified. This information was provided to study coordinators, who assigned women on open lists to the mammography group or the control group,” Dr. Monsees says.

“Those of us in the imaging field know that the quality of mammography is only as good as the weakest link in the imaging chain. This study had far too many weak links. These criticisms are not new; they were raised during and after the trial and remain valid today.”

Dr. Pearlman does not believe that the Canadian trial reflects modern breast cancer screening.

“There are things in the Canadian trial that differ from what we see in modern mammography,” he says. “In the Canadian trial, in women diagnosed with breast cancer, they noted whether there was a palpable mass in the area of cancer. In the Canadian trial the percentage of palpable masses was approximately 66%, and that’s very very different from what we see with modern mammography. In current practice, about 15% of breast cancers diagnosed by mammography are palpable. And so it appears that, for some reason, they were seeing more advanced breast cancers when they were screening by mammography.”

Another concern focuses on the technology used in the trial.

“It appears that the Canadian investigators pulled old machines into service for the trial,” Dr. Pearlman says.

In addition, more recent advances, such as digital mammography and tomosynthesis, were not available at the time of the Canadian trial.

“Overall, the Canadian trial appears to be looking at a different group of women than what we typically see in the United States in women diagnosed with breast cancer,” says Dr. Pearlman. “And if they were, then it makes sense that there would be no benefit in mortality, since they were detecting more advanced breast cancers in that population.”