Does Screening at 40-49 Years Boost Breast Cancer Survival?

VANCOUVER, British Columbia — Canadian women aged 40-49 years at no or moderate risk for breast cancer who participated in organized mammography screening programs had a significantly greater breast cancer 10-year net survival than similar women who did not participate in such programs, according to data presented here at the Family Medicine Forum 2024. 

The data call into question draft guidelines from the Canadian Task Force on Preventive Health Care, which suggest not systematically screening women in this age group with mammography.

Overdiagnosis Challenged

Given that some jurisdictions in Canada have organized screening programs and some do not, there was an opportunity to compare breast cancer 10-year net survival of women who lived in jurisdictions with and without such programs, explained family physician Anna N. Wilkinson, MD, associate professor at the University of Ottawa, Ontario, Canada and Ottawa regional cancer primary care lead.

“The question was [whether] we could use big cancer data to figure out what’s going on,” she told Medscape Medical News. 

To investigate, Wilkinson and co-investigators reviewed data from the Canadian Cancer Registry linked to mortality information and assessed outcomes for women aged 40-49 and 50-59 years diagnosed with breast cancer from 2002 to 2007. They compared 10-year net survival estimates in jurisdictions with organized screening programs for 40- to 49-year-olds with jurisdictions without them. 

“Net survival is important because it’s a survival measure that looks at only the cancer in question,” Wilkinson explained.

Investigators determined breast cancer to be the primary cause of 10-year mortality in women aged 40-49 years diagnosed with the disease (90.7% of deaths). 

Furthermore, the 10-year net survival in jurisdictions that screened these women (84.8%) was 1.9 percentage points higher than for jurisdictions that did not (82.9%). 

The difference in 10-year net survival favoring jurisdictions that offered screening was significant for women aged 45-49 years (2.6 percentage points) but not for those aged 40-44 years (0.9 percentage points).

Given that 90% of the deaths in women in their 40s who had a breast cancer diagnosis were due to breast cancer, Wilkinson challenged the concept of women in their 40s being overdiagnosed with breast cancer, meaning that the cancers detected were indolent and did not require treatment nor result in death.

Earlier detection would generally mean finding disease at an earlier stage and the need for less invasive treatment, she noted. “And one of the biggest benefits [of screening women in their 40s] is that you have diagnosis at earlier stage disease, which means fewer intensive therapies, less time off work, less long-term morbidity, and less cost to our healthcare system.”

Modeling Shows Little Screening Benefit

The task force’s draft guidelines, released earlier this year, were based on evidence from 165 studies including randomized, controlled trials, observational studies, time-trend studies and modeling. They suggest not systematically screening women 40-49 with mammography who are not high risk.

Family physician Guylène Thériault, MD, chair of the task force and its breast cancer working group, and director of the Pedagogy Center at the Outaouais Campus, McGill University, Montreal, explained that to come to that conclusion, the task force had assessed the impact of organized screening for women in Canada aged 40-49 years and calculated the impact of mammography for every 1000 women over 10 years.

The model suggested that screening would yield 368 false positives, leading to 55 biopsies, and then to a breast cancer diagnosis in 19 women. Of those 19, the task force estimated 17 or 18 would not die of breast cancer over 10 years, two would be treated for breast cancer that would not have caused problems, ie\ overdiagnosis, and one to two would die of breast cancer.

Without screening, on the other hand, the model suggested that 983 of 1000 women aged 40-49 years would not be diagnosed with breast cancer, and 17 would be, 15 of whom would not die from breast cancer over 10 years (no overdiagnosis, no deaths prevented) and two would die.

It is important that family physicians provide their patients with this information to assist in shared decision making about screening, Thériault said.

Wilkinson concluded that screening programs that included women in their 40s were associated with a significantly higher breast cancer 10-year survival, without an increased rate of diagnosis. She suggested that the study findings inform the screening guidelines for women aged 40-49 years. Stay tuned.

The study was supported by the University of Ottawa’s department of family medicine. 

Wilkinson, MD, is a consultant for Thrive Health. Thériault, MD, disclosed no relevant financial relationships.