Last November, a Canadian task force of medical professionals concluded women in their 40s at average risk of developing breast cancer should not be routinely screened with mammography. The potential harms of so-called false positives and unnecessary biopsies outweighed the potential benefits of screening in average-risk women, the Canadian Task Force on Preventive Health Care guidelines said, stoking an ongoing and contentious debate.
The task force made five additional breast cancer screening recommendations for average-risk women, including on the use of magnetic resonance imaging and breast self-exams. Three Sunnybrook staff with expertise in breast cancer care and imaging recently sat down to discuss all the recommendations.
“Women should really seek out information to find out if they really are average risk, because many women aren’t aware of the full impact, for example, of family history on both sides of the family and other risk factors that may increase their risk of breast cancer.”
Dr. Andrea Eisen, co-chair of Cancer Care Ontario’s Breast Site Group, is head of Sunnybrook’s Familial Cancer Program, which provides risk assessment of hereditary cancer syndromes to patients and their families with a focus on breast, ovarian and colorectal cancers.
“From personal experience, having had callbacks for mammograms and biopsies that turned out to be benign, it’s incredibly stressful... There are more women who have the stress that turns out to be for nothing, than there are women who actually have their cancer diagnosed.”
Dr. Ellen Warner is a medical oncologist at Sunnybrook’s Odette Cancer Centre who led a study proving the benefits of adding MRI to mammography for screening very high-risk women. She is also the author of a recent review article in the New England Journal of Medicine on breast screening for average-risk women.
“The reason the Canadian Task Force on Preventive Health Care have taken this position is they believe the benefits of the lives saved through screening are not much greater than those harms. I disagree strongly with the recommendations.”
Dr. Martin Yaffe, PhD and senior imaging scientist at Sunnybrook Research Institute, led the invention of digital mammography and is co-leader of the Smarter Imaging Program, an initiative of the Ontario Institute for Cancer Research.
What are your thoughts on the task force’s recommendation on screening mammography for women who are in their 40s?
DR. YAFFE: I disagree with the task force recommendations. Most women don’t have breast cancer. The whole idea behind screening is that you’re trying to find breast cancer in the few women who do, so there is the opportunity to save their lives through earlier treatment.
The task force looked at eight trials of screening with mammography and they pooled the data from those eight trials. Across the board they found about a 15 per cent mortality reduction from screening women in their 40s. They compared that to what they considered to be the harms of screening, including what we refer to as false positives, over-diagnosis and over-treatment.
The reason they have taken this position is they believe the benefits of the lives saved through screening are not much greater than those harms. I disagree strongly with the recommendations. First of all, the 15 per cent mortality reduction they identified is a gross underestimate because it’s based on old mammography done in a time when imaging was primitive compared to what it is today. Seven of those trials were done in the 1960s, ’70s and ’80s. The eighth and most recent one finished just after 2000, and there, when you look at the women who actually did receive the mammography, the result was a 24 per cent mortality reduction from screening women in their 40s.
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