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Canadian provinces and territories that allowed women aged 40-49 to self-refer for organized breast cancer screening programs had lower breast cancer mortality rates compared with those that did not, a new study says.Michael Hanschke/Reuters

Canadian women diagnosed with breast cancer in their 40s were more likely to be alive 10 years later if they lived in a province with an organized screening program that permitted women of their age to refer themselves for mammograms, a new study says.

Researchers from Statistics Canada and the Ottawa Hospital concluded that, in provinces they defined as “screeners,” 84.8 per cent of women diagnosed in their 40s survived for at least a decade, compared with 82.9 per cent of women in provinces that make it difficult to get a mammogram before age 50 – an absolute difference of 1.9 percentage points.

The study could not determine whether it was mammogram access or something else that improved survival. (Only a randomized control trial might be able to do so.) It just shows that higher 10-year survival rates correlate with residing in a province where organized breast-cancer screening programs include women in their 40s.

However, University of Ottawa radiology professor Jean Seely, an author of the study, believes the findings are, “such an underestimation of the benefit of screening,” because even in provinces with the most welcoming approach, Statscan surveys suggest barely half of women in their 40s get regular mammograms.

Wilkinson: As a cancer ward doctor, I see the tragic results of the lack of early breast cancer screening

The new paper, published Friday in the Journal of Clinical Oncology, is the latest salvo in the Canadian mammogram controversy, which is expected to heat up again this fall. That’s when the Canadian Task Force on Preventive Health Care is scheduled to release the first update to its breast-cancer screening advice since 2018.

The study, which drew on data from the Canadian Cancer Registry, included 21,103 cases of invasive breast cancer diagnosed in women 40 to 49 between 2002 and 2007, with follow-up data to 2017.

In May, the United States Preventive Services Task Force released a draft recommendation lowering the starting age for mammograms to 40 from 50.

The current Canadian guidelines recommend against screening mammograms for average-risk women under 50, largely because the authors consider the risks of false positives and over diagnosis to outweigh the benefits for young women, who have lower rates of breast cancer than their older counterparts.

However, the Canadian guidelines, which don’t apply to women with known risk factors such as a family history of breast cancer, say that women 40 to 49 who want a mammogram should be able to get one through “shared decision-making” with a doctor.

Although the Canadian guidelines are national, provincial and territorial governments take different approaches to mammograms, which are low-dose X-rays of the breast.

Some allow women in their 40s to self-refer, without a doctor’s endorsement, to an organized program that includes annual recalls. Others require women in that age bracket to find a doctor willing to refer them for a screening mammogram. (Screening refers to tests done on people with no symptoms. A woman who finds a lump in her breast can ask her doctor for a mammogram referral, but that wouldn’t count as screening.)

Dr. Seely, who is also the head of breast imaging at the Ottawa Hospital, and her co-authors took advantage of divergent provincial and territorial policies to design a study that divided jurisdictions that screen women in their 40s – defined as places with organized programs that include self-referral and annual recall – and those that don’t.

The screening jurisdictions were British Columbia, Alberta, Nova Scotia, Prince Edward Island and the Northwest Territories. The rest were designated as comparators, except for Nunavut, which was excluded because of lack of data.

The study found a 1.9 percentage point difference in 10-year net survival rates between women in screening and comparator jurisdictions.

The survival benefit was more pronounced in women 45 to 49. There was a 2.6 percentage point survival benefit for women in that bracket, which Anna Wilkinson, a GP-oncologist at the Ottawa Hospital and another author of the study, said approached the survival benefit seen with tamoxifen, a widely used treatment for breast cancer.

For women 40 to 44, however, the difference was a statistically insignificant 0.9 percentage points.

Backers of the Canadian task force’s current recommendation against screening women for breast cancer in their 40s have long been critical of taking into account observational studies that can’t prove cause and effect, preferring to rely on randomized control trials of screening mammography, the majority of which are decades old.

However, the task force has indicated it is widening its net beyond RCTs in the current review. Ottawa gave the panel an extra $500,000 to expedite the process.

Guylène Thériault, a Quebec family physician and co-chair of the Canadian task force, said panel members would evaluate the new study to see whether it fits their criteria.

“We want to hear from as many sources as possible to help inform the breast cancer screening guideline update,” Dr. Thériault said in a statement.

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