The draft guidelines stem from a review of more than 165 recent randomized controlled trials, observational studies, mathematical models, and other data.
The guideline working group included four breast cancer experts (a medical oncologist, a radiation oncologist, a surgical oncologist, and a radiologist), three patient partners, six family physicians, a nurse practitioner, evidence review teams, and other experts.
To avoid potential conflicts of interest, the oncologists provided input but did not vote on the final recommendations, Guylène Thériault, MD, a family physician and chair of the task force and Breast Cancer Working Group, said in an interview.
The guideline recommends that, after the potential benefits and harms of screening have been considered, mammography should be accessible every 2-3 years to women (ie, people assigned female at birth) between ages 40 and 74 years who are at average or moderately increased risk.
Women with a personal or extensive family history of breast cancer or genetic mutations that would increase breast cancer risk; those who have symptoms, such as a lump; those who feel they may be at high risk; and those who are transgender women should consult a healthcare provider about appropriate options, according to the updated guidelines, which do not apply to these patients.
The draft guidelines were published online on May 30 and are open for public comment until August 30.
‘Three Big Questions’
To develop the guidelines, the work group asked “three big questions,” said Dr. Thériault. The first was the effectiveness of breast cancer screening for women aged 40 years and over. For this question, this systematic review, unlike the 2018 guideline update, included not only randomized trials but also observational data to ensure that the work group considered all available data.
“The second question was about comparative effectiveness,” which is something the United States considered for the latest US Preventive Services Task Force (USPSTF) update, said Dr. Thériault. The USPSTF asked questions such as “What happens if we start screening patients at age 40 years? Or at age 50 years? What happens if we stop at age 74 years? Or if we use different tests such as 3D versus digital mammography?”
The Canadian Task Force relied on the evidence that the USPSTF found after grading it with its own criteria, she said. The results were similar, and so are the recommendations in this area. “For example, we don’t recommend supplementary screening for women with dense breasts because there are no studies to inform patient-oriented benefits.”
The third question was about the values and preferences of women regarding breast cancer screening, which is something the United States didn’t examine. “We had looked at that issue in 2018, and this time around, even though we expanded the type of studies, we got the same message: That there are differences between women in their 40s and those who are age 50 years and over.”
“The majority of women in their 40s think that the harms outweigh the benefits and are not interested in screening,” said Dr. Thériault. “But when I say the majority, that’s not every woman. So, we had to recognize that there is variability. And the majority, but not all, of women ages 50-74 years thinks the benefits are higher than the harms. That’s why we say in our recommendation that from ages 40 to 74, it’s a personal choice.”