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Ontario is lowering the age at which women can start self-referring for mammograms to 40 from 50, a policy shift the province unveiled even before a national task force releases its review of Canada’s breast-cancer screening guidelines.

The plan, which takes effect in the fall of 2024, is expected to result in an additional 130,000 women getting mammograms every year, Ontario Health Minister Sylvia Jones said. “Every cancer that we discover earlier means a less invasive treatment and better outcomes,” she said in an interview after the announcement. “It just gives patients options, really.”

The question of when to start screening for breast cancer has been hotly debated in Canada for years, but the temperature of the discussion rose after an influential U.S. task force published draft guidance in May urging women aged 40 to 49 to get mammograms every two years.

That advice differed from Canada’s. The Canadian Task Force on Preventive Health Care, in a document last updated in 2018, recommended against regular screening for average-risk women in their 40s, saying the benefits of early detection were outweighed by the harms of false alarms and overdiagnosis of slow-growing cancers that might never have caused a patient harm. Despite that conclusion, the Canadian guidelines also say patients in their 40s who really want a mammogram should be able to get one through “shared decision-making” with a doctor.

After the U.S. panel released its new advice, Ottawa gave the Canadian task force an extra $500,000 to expedite a regular review of its guidelines, the results of which are supposed to be published late this fall.

Although influential, the Canadian task force’s recommendations aren’t binding. Most provinces and territories hew closely to the official advice, but there are exceptions, including Alberta, which last year lowered its starting age to 45, and British Columbia and Nova Scotia, which allow women in their 40s to self-refer for mammograms.

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Today in Ontario, women in their 40s can get a mammogram if they have a doctor willing to write a referral. When the policy changes in a year, women in that age bracket will be able to refer themselves, regardless of whether they have a co-operating doctor or a doctor at all.

Martin Yaffe, a senior scientist at Sunnybrook Health Sciences Centre whose research focuses on early detection of breast cancer through imaging, said he hoped Ontario’s announcement would either affect the task force’s final recommendations or make their advice less influential.

“I think they should be irrelevant unless they exercise a major change in how they look at things, because I think their recommendations have been harmful to women,” Dr. Yaffe said.

Other experts say the case for mammography in women aged 40 to 49 is less clear. Steven Woloshin, a general internist and co-director of the Center for Medicine and Media at The Dartmouth Institute in New Hampshire, recently co-authored a piece in the New England Journal of Medicine opposing the U.S. draft recommendations on the grounds they don’t give women enough latitude to make an informed decision that seriously considers the data on harms of false alarms and overdiagnosis.

“You can’t make an informed decision if you don’t have the data,” Dr. Woloshin said.

As for the Canadian Task Force, its co-chair, Guylène Thériault said in a statement on Monday that panel members continue to “focus on our evidence-based work and look forward to sharing our results with the goal of providing credible and unbiased recommendations to support the health and well-being of women.”

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