Studies that shaped Canada’s breast cancer screening guidelines ‘flawed,’ researchers say

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A group of Canadian and US researchers say they have found “significant flaws” in the studies that have shaped Canada’s modern breast cancer screening guidelines.

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one in new comment, they suggest that lives have been lost because of methodological errors in two Canadian trials that found mammograms did not reduce mortality from breast cancer for women in their 40s.

However, seven other trials conducted around the world found the opposite: mammograms for women reduced mortality in that age group.

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“It is deeply saddened to learn that the impact of these flawed studies on screening policies has resulted in women losing their lives,” Dr. Paula Gordon, a radiology researcher and clinical professor at the University of British Columbia, said in a news release on Wednesday.

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“We hope that shedding light on these key problems will encourage policymakers to revisit existing guidelines.”

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The commentary paper was written by Gordon and colleagues from the Toronto-based Sunnybrook Research Institute, Ottawa Hospital, the University of Alberta and Harvard Medical School. Posted in Journal of Medical Screening This week.

The 1980s study, known as the Canadian National Breast Screening Study (CNBSS), had two trial groups, but the paper says that most women had a clinical breast exam before being placed in the groups.

They should have been placed randomly into test groups, but in some cases, their breast exam results influenced which group they were placed in, the authors claimed, using staff interviews and whistleblower testimony, among other types of evidence. By citing.

He noted that more women who were already ill with cancer ended up in the group receiving mammograms. Over seven years, more of those women died compared to a group with fewer ill women, supporting a study “bias” against the effectiveness of mammograms in preventing death in routine care and physical exams.

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“Given these important issues, the test results are unreliable and should not be used to inform policies on breast cancer screening,” said lead author Dr Martin Yaffe from Sunnybrook Research Institute.

Yaffe’s research found that “even a small imbalance” in the assignment of women entering the CNBSS with advanced cancer would make its results far from showing a lower mortality rate.

One possible reason for the imbalanced tests, the authors theorize, is that a nurse with “good intentions” urged that women whose breast exam revealed lumps or other findings be placed in a trial group who should have a mammogram immediately.

Dr. Anthony Miller, who led the original CNBSS, called the commentary’s claims “false” and said that there is “good evidence” of randomization of female study participants in the 1980s. He persisted with the preliminary tests and their findings, published in 1992.

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“I don’t think this is a study at all,” Professor Emeritus Dalla Lana School of Public Health at the University of Toronto said in an interview after reading the published paper.

“It’s some people whose jobs depend on mammography decide to once again attack Canada’s National Breast Screening Study because we didn’t see a benefit from mammography.”

The CNBSS is the only breast screening study in the world that was able to aggregate breast cancer risk factors in all the women who participated, he said. He said the commentary paper would “mislead” the public.

“I do not believe that mammography screening is beneficial,” he said.

“Mammography is a good tool for diagnosis if women have reasons to be concerned about their breasts, and as such should be used – as a diagnostic tool.”

Used for screening, mammograms can do “all kinds of weird things,” like detect lesions that don’t progress to something harmful, he said. Ultimately, they can lead to potentially dangerous “over-treatment.”

Concerns about the study’s findings and its randomization have been reported for years.

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In 1997, however, a external check The research “failed to uncover credible evidence” that the random assignment of women to trials was “distorted” in any way. The report said that even if there was sabotage, it would have been minimal and “could have had only a minor effect” on the findings.

In 2019, the Canadian National Breast Screening Study was named in the British Medical Journal top five research papers of the decade

Susan Kinghorn, a medical radiation technologist who worked on the CNBSS, said she was given a list of 10 or 12 study participants at the beginning of the day who were to receive mammograms.

She told Granthshala News that she was considered random based on a list of 20 to 24 women, but sometimes the names of the women on her original list were changed after a physical breast exam.

“I was told I didn’t have to question it, I just had to go ahead and do it because ‘Mrs. Smith needed to have a mammogram,'” she said. “Suppose there was a Mrs Jones on the list, later in the day they would remove Mrs Jones from the list, and Mrs Smith has replaced Mrs Jones.”

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Kinghorn always had 10 to 12 names in total, and although it “wasn’t perfect” she said she was a fresh graduate and was grateful to have the job. When she asked the question, she said her concerns were dismissed and that what really mattered was that the patients were “checked out.”

In the end, Kinghorn completed only four to five weeks of his three-month contract on the trial study.

As it stands, the Canadian Task Force on Preventive Health Care does not recommend Routine mammograms for women between 40 and 49 unless they have pre-existing conditions or are at higher-than-average risk.

NS…

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