All provinces and territories should lower the starting age for breast cancer screening to 40, the Canadian Cancer Society said Thursday.

Some provinces already pay for mammograms starting at age 40, but the current guideline set by a national task force advises beginning breast cancer screening at age 50.

It's critical for women across the country to have "timely access to breast screening, no matter where they live," said Sandra Krueckl, the cancer society's executive vice-president of mission, information and support services.

"There's strong enough evidence from trials, from modelling studies and from real-world data to warrant that shift to 40," said Krueckl in an interview.

"We have been hearing for a long time now that there's concern about (women) age 40 to 49 and their ability to access (screening)."

About 13 per cent of breast cancer cases in Canada occur in women in that age group, Krueckl said.

Earlier diagnosis often means less invasive treatment is required and outcomes are more successful, she said.

The Canadian Task Force on Preventive Health Care, which sets clinical guidelines to help family doctors and nurse practitioners decide whether and when to suggest screening, currently recommends routine screening starting at age 50 for people at average risk of breast cancer.

The task force is scheduled to revise its guidance this spring, but said in an email that a "detailed" review of clinical trials, international best practices and other data is still underway and did not confirm what the updated advice will be.

"The Canadian Task Force respects the Canadian Cancer Society and its important work," it said.

"We look forward to discussing the draft recommendations on screening for breast cancer from our comprehensive evidence review later this spring."

Even if the task force recommends that screening begin at age 40, it's ultimately up to the provinces and territories to fund it, the cancer society said.

It's also "critically important" for primary-care providers to talk with their patients about breast cancer screening starting at 40 and not wait until they turn 50, Krueckl said.

"We also know that Black women are being diagnosed before age 50 more frequently and with more advanced disease," she said.

One in eight women in Canada is expected to be diagnosed with breast cancer in their lifetime, the cancer society says.

These are the starting ages for breast cancer screening in each province and territory, according to the Canadian Cancer Society:

  • In British Columbia, Nova Scotia, Prince Edward Island and Yukon, women can refer themselves for breast screening starting at age 40. 
  • Screening is available starting at age 45 in Alberta and the Northwest Territories. 
  • Ontario and New Brunswick have both committed to lowering the minimum age for screening from 50 to 40 in 2024.  
  • Saskatchewan has said it will lower screening eligibility to age to 40 in a "phased-in" approach starting in 2025. 
  • Manitoba, Quebec and Newfoundland and Labrador's screening programs continue to begin at age 50 
  • Nunavut has no organized breast screening program.

This report by The Canadian Press was first published May 9, 2024.