A new Canadian commentary has reopened the emotional debate on the benefits of early breast-cancer screening, suggesting that over-diagnosis from mammogram use and the resulting, unnecessary treatment outweighs the limited advantages of the tests, at least in women under 50.
Cornelia Baines, a University of Toronto public health professor, also charges that the debate over mammograms has become dominated by vested interests, including the companies that make diagnostic imaging machines and the radiologists who analyze the scans — and whose associations are funded by those firms.
New proposals and government funding to expand breast-cancer screening to younger groups of women simply do not seem justified by the scientific evidence, Dr. Baines’ paper in the journal Open Medicine argues.
“It’s not just the issue of how big the benefit is — and it’s clearly very, very small — it’s the risk that it puts other women to, in terms of having over-diagnosed breast cancer — in other words breast cancer that won’t kill them,” she said in an interview. “That to me is a major wake-up call to women, if they wanted to listen.”
The question of how widely to screen for breast cancer has been heated at times, peaking a year and a half ago when the U.S. preventive services task force, an advisory body of doctors and scientists, recommended that women who are not at unusual risk begin getting mammograms at 50, not 40 as many U.S. experts had earlier advised. The proposal was denounced by some medical groups, cancer survivors and politicians, with members of the panel labelled “idiots” and their report derided as a plot by the Obama administration to put cost-cutting above health. In the end, the U.S. government disavowed the group’s findings.
In Canada, Dr. Baines’ provocative article comes months after the Ontario branch of the Canadian Breast Cancer Foundation issued a report — based on a consensus of experts at a conference — recommending that women at average risk of the disease should begin having yearly mammograms at age 40. The 2011 Ontario budget, meanwhile, allocated $10-million to screening of high-risk women aged 30 to 49.
Dr. Baines maintains there is scant evidence for either proposition.
She cited the U.S. task force’s conclusions that 1,900 women between 39 and 49 would need a mammogram every year for 10 years to prevent one breast-cancer death. For women in their 50s, 1,339 need to be screened yearly to save one life, and for those in their 60s, 377 women.
What is more, studies suggest that 25% of the cancers detected by mammograms would never have caused symptoms or proven fatal without any screening, Dr. Baines notes. In those cases, the result can be needless mastectomies or lumpectomies, a life-long side effect of screening that is rarely raised with patients before getting their mammogram, she said.
Representatives of the breast-cancer foundation and the Canadian Association of Radiologists were not available for comment Tuesday.
In its report urging screening of women in their 40s, the foundation argued that population-wide statistics overlook the potential benefits for individual women — the relatively few who might die without it.
“Screening is one of the few options available to get ahead of random chance and detect a tumour early,” it said. “In most cases, the earlier the treatment begins, the better the prognosis.”
The foundation’s report also said that less than 10% of tumours found in screening could be considered over-diagnosis, not 25%, as Dr. Baines maintained.
A spokeswoman for the Canadian Cancer Society said her organization does not urge that average-risk women in their 40s get regular mammograms.
The effects of screening on women under 50 have not been studied extensively and the evidence that does exist suggests the benefits are unclear, said Heather Chappell, the society’s director of cancer-control policy.
The hard data, though, often takes a back seat in the debate, she acknowledged.
“Everyone has the best intentions, of helping women,” said Ms. Chappell. “[But] sometimes the discussion can be more emotional, rather than based on evidence.”
Dr. Baines goes further, suggesting that what some have called the “mammography wars” are fuelled in part by self-interested manufacturers of imaging equipment and radiologists.
Regardless of motives, the debate can be “vicious,” she said. When she and colleagues published results of a trial in 1992 that questioned the benefits of early screening, a U.S. radiologist wrote to suggest she commit suicide, because “I was murdering so many women.”