Last month, a national U.S. task force finalized its guidance that recommends routine mammography start at 40.Eric Gaillard/Reuters
A highly anticipated update to Canada’s national breast screening guidelines says people in their 40s shouldn’t be routinely screened for the disease, but also shouldn’t be stopped from getting a mammogram if they want one.
The Canadian Task Force on Preventive Health Care is releasing its new recommendations Thursday as the debate over the right time to start screening for average-risk individuals is becoming increasingly polarized, leading some organizations and provinces to shift their positions.
Earlier this month, the Canadian Cancer Society released a new position statement calling for routine breast screening to begin at the age of 40. The government of Newfoundland and Labrador also announced this month that it’s lowering its recommended screening age to 40, after a similar move by Ontario last fall. Last month, a national U.S. task force finalized its guidance that recommends routine mammography start at 40.
Despite the changes, Guylène Thériault, co-chair of the national task force, said panel members and expert advisers didn’t find compelling scientific evidence that would warrant a lowering of the screening age for average-risk individuals. Instead, the guidelines are focused on providing information to help people at various ages determine whether screening is right for them.
“I don’t think that in this day and age, any woman should just go get in line and get screened,” she said. “They should have the information because there are benefits and there are harms.”
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The new version makes it clear that individuals who want screening, after being told about the possible risks and benefits, should be able to access it every two to three years. People aged 50 to 74 should be offered screening every two to three years, but for those 75 and older, evidence shows that the harms likely outweigh any benefit, the guidelines say.
One of the central questions the task force faced was how to properly balance the potential benefits of screening mammography with the possible harms. While the evidence is clear that screening mammograms can play a pivotal role for women in their 50s and beyond, the age at which breast cancer incidence goes up dramatically, it’s less clear for people in their 40s. According to the Canadian Cancer Society, 13 per cent of breast cancer cases occur in people in their 40s in Canada, and there has been a small, quarter-of-a-per-cent increase in that age group in recent years.
But the potential benefit of detecting cases in that age group must be weighed against the risks, which include unnecessary biopsies, overdiagnosis of cancer that would not have posed a health risk, as well as the fear and anxiety that occur when people undergo avoidable follow-up procedures.
The guidance also says that there’s no evidence that supplemental screening with MRI or ultrasound leads to better outcomes for people with dense breasts. And the same was true for women with a family history or other predisposition to the disease. But the guidelines emphasize the need for individuals to make their own choices after looking at the available information.
Dr. Thériault noted that the task force included a wide range of evidence, as well as analyses of women’s values and preferences around screening, to come to its conclusions. And while many proponents suggest earlier screening starting at age 40 will save lives, the data are less clear. Dr. Thériault noted that 1,000 women would have to be screened for 10 years to prevent one breast cancer-related death. And several women in that group would undergo unnecessary biopsies or experience overdiagnosis of cancer.
She said she’s open to seeing evidence that shows otherwise and that the guidelines will be open to a public consultation process to seek additional feedback.
“If we missed something, we will go back and look at it,” Dr. Thériault said.
Michelle Nadler, a medical oncologist with the Princess Margaret Cancer Centre in Toronto who was an expert adviser to the task force, said that while screening mammograms are important, using them more often in younger age groups doesn’t necessarily equate to better patient outcomes.
“We know that the more aggressive a cancer, the more likely it may occur in between screens,” Dr. Nadler said. “Screening helps some people, but it doesn’t help everybody.”
Breast cancer screening refers to programs that look for cancer in people who are not experiencing any symptoms. If an individual has symptoms, such as a lump, the mammogram is used to diagnose, not screen. And the current screening guidelines don’t apply to people who have a family history or genetic mutations that put them at a higher risk for breast cancer.
Studying the benefits of screening is incredibly complex, in part because there are a number of inherent biases in the interpretation of the data. For instance, a person who undergoes breast screening and is diagnosed with cancer may live for another 10 years. But if that same person chose not to get screened and was only diagnosed years later, after developing symptoms, she could still die at the same time. In other words, it’s difficult to ascertain when screening “saves” lives.
But studies of breast cancer mortality are more reliable and less prone to the bias of survivor-based studies. Breast cancer mortality for women in their 40s has steadily declined in recent decades. And last fall, a paper in the New England Journal of Medicine found that in Switzerland and Denmark, which don’t routinely offer screening to women in their 40s, breast cancer mortality was lower than in the United States, where around 60 per cent women in that age group get screened.