A recommendation from an influential United States panel that women begin receiving mammograms at 40 instead of 50 has reignited a long-smouldering fight over whether Canada should encourage women in their 40s to get screened for breast cancer.
The U.S. Preventive Services Task Force lowered the age by a decade in large part because the number of American women diagnosed with breast cancer in their 40s has increased by 2 per cent a year since 2015, a faster growth rate than in the past.
The U.S. recommendation is expected to have some sway in Canada, despite breast-cancer diagnoses among Canadian women in their 40s growing more slowly – 0.5 per cent a year since 2015 – than in the U.S., according to Statistics Canada data provided to The Globe and Mail.
Debates over Canadian mammography guidelines have raged for years. The fights often pit breast-cancer advocates and medical specialists who favour earlier and more frequent screening against the Canadian Task Force on Preventive Health Care, a federally appointed panel that has concluded the harms of false positives and overdiagnosis outweigh the benefits of mammograms for some groups.
In a recent twist, the Canadian Cancer Society in December withdrew its support for the task force’s mammography advice, saying the science had evolved enough to merit a fresh look. The Canadian task force was already planning to revisit its breast-cancer screening recommendations this year.
Funded by the Public Health Agency of Canada, the Canadian Task Force on Preventive Health Care produces evidence-based guidelines for the family doctors and nurse practitioners who deliver most primary care.
The task force’s breast-screening guidelines, last updated in 2018, recommend women 40 to 49 not be screened with mammography. The recommendations also say that women in their 40s who want a mammogram should be able to get one through “shared decision making” with their doctors, but many provinces have policies that make that difficult.
Guylène Thériault, a member of the Canadian task force, said women in their 40s shouldn’t feel “obligated” to get regular mammograms, especially considering the anxiety that can arise from false positives and the real harms of treating women for small and slow-growing cancers that might never make them sick.
“They should ask for the pros and cons and we should have the respect for our patients to tell them there are pros and cons,” said Dr. Thériault, also a family physician in Gatineau.
A December report by the Public Health Agency of Canada’s office of audit and evaluation found the task force “consistently used a balanced mix of clinical and methodological expertise [for] its guideline development process by engaging with a wide variety of internal and external partners and stakeholders,” but hasn’t met its commitment of producing three guidelines a year since 2018, in part because members are unpaid volunteers with other jobs.
The Public Health Agency of Canada’s office of audit and evaluation submitted a report in December that found the task force “consistently used a balanced mix of clinical and methodological expertise [for] its guideline development process by engaging with a wide variety of internal and external partners and stakeholders,” but hasn’t met its commitment of producing three guidelines a year since 2018, in part because members are unpaid volunteers with other jobs.
Paula Gordon, a clinical professor of radiology at the University of British Columbia and a former medical director of the breast program at B.C. Women’s Hospital, does patient-engagement work through one of the groups that opposed the task force’s advice, the Canadian Society of Breast Imaging.
Dr. Gordon said she’s heard “over and over and over again” from younger women who begged their family doctors for a mammogram, only to be told they didn’t need to be screened before 50. “And then they had a big breast cancer when they were in their 40s. So it’s not rare. And it’s devastating to those people and their families.”
She and some other doctors criticize the task force for limiting its review of the evidence for mammography to randomized control trials. Dr. Thériault of the task force said it was vital for the panel to rely on the highest-quality studies and RCTs are the gold standard.
However, most of the RCTs evaluating mammography are decades old; the eight trials the Canadian task force relied on for the 2018 guidelines were begun between 1963 and 1991.
In its draft guidelines released Tuesday, the U.S. task force concluded the RCT evidence for mammography hadn’t changed meaningfully since the panel’s last recommendations in 2016. The group changed its stand primarily because of rising breast-cancer diagnoses for U.S. women in their 40s, said John Wong, a general internist at Tufts University in Massachusetts and member of the panel.
The U.S.’s inability to close the gap between white women and Black women – who are approximately 40 per cent more likely to die from breast cancer – also played a role, he said.
It’s not clear why more fortysomething women in the U.S. are getting breast cancer, but when task force researchers plugged the higher incidence rates into mathematical models, “we found that we have the potential to save about 20 per cent more lives by moving the start age to 40,” Dr. Wong said. That led the panel to advise average-risk women 40 to 74 to get a mammogram every two years.
The Canadian guidelines from 2018 didn’t use the kind of modelling that was pivotal in the new U.S. recommendation.
Anna Wilkinson, a GP-oncologist at the Ottawa Hospital, urged the Canadian task force to consider a wider variety of evidence. She was one of the authors of a study published last summer in the journal Current Oncology that used data from the Canadian Cancer Registry to find that provinces that screen women in their 40s every year had lower proportions of advance breast cancer compared with women in their 50s from provinces that don’t hold annual mammograms.
(Despite the task force recommending against mammograms for women in the 40s, some provinces allow women to self-refer for screening and offer annual callbacks to those who want them.)
“Our research showed that if we screen women in their 40s, their cancers are diagnosed at much earlier stages, when they’re way more treatable,” Dr. Wilkinson said. “Their survival is better, the side effects of the treatment are better, and they’re less likely to die.”
Editor’s note: An earlier version of this article incorrectly said the U.S. task force recommends mammograms for ages 40 to 79, when it is in fact 74. The earlier version also said some breast-cancer patient groups and medical societies helped persuade the federal government to order a wholesale review of the Canadian Task Force on Preventive Care. In fact, their advocacy had no role in the Public Agency Health of Canada conducting a regularly scheduled audit of the task force.