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Researchers say the studies that shaped the Canadian breast cancer screening guidelines are “defective.”

A group of Canadian and American researchers say they found a “significant flaw” in the work that shaped Canada’s modern breast cancer screening guidelines.

A new commentary suggests that a methodological error in two Canadian trials found that mammograms for women in their 40s did not reduce breast cancer mortality.

However, seven other trials conducted around the world found the opposite. Female mammograms have reduced mortality in that age group.

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In a news release at the University of British Columbia, radiologist and clinical professor Dr. Paula Gordon learns that these flawed studies have affected screening policies and have resulted in the loss of women’s lives. Is painful. “

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“We hope that by shedding light on these key issues, policy makers will be able to revisit current guidelines.”

The commentary was written by Gordon and colleagues at the Toronto-based Sunnybrook Institute, Ottawa Hospital, University of Alberta, and Harvard Medical School.Was published in Journal of Medical Screening this week.


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A study in the 1980s, known as the Canadian National Breast Screening Study (CNBSS), had two study groups, but according to this paper, most women had a clinical breast exam before joining the group.

They should have been randomly placed in study groups, but in some cases the authors argued that they influenced which group the breast test results were placed in, including staff interviews and whistleblower testimony. I quoted the evidence.

Many of the women who already have cancer are in the group that received the mammogram, they said. For over seven years, many of these women died more than the less sick women, and supported studies of “bias” in the effectiveness of mammogram mortality prevention in routine care and physical examination.

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“Given these serious issues, the test results are unreliable and should not be used to inform breast cancer screening policies,” said Dr. Martin Jaffe, lead author of the Sunnybrook Institute. increase.

According to a Yaffe study, “even a slight imbalance” in the allocation of women who participated in CNCS with advanced cancer, the results will shift from showing reduced mortality.

A possible reason for the imbalanced exam is that a “good faith” nurse urged women who had lumps or other findings on breast examinations to join the exam group for immediate mammograms. is.


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Dr. Anthony Miller, who headed the original CNCS, called the commentary claim “wrong” and said there was “good evidence” of randomization of female research participants in the 1980s. He endorsed the first trial published in 1992 and its findings.

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“I don’t think it’s research at all,” said an emeritus professor at the University of Toronto’s Dalla Lana School of Public Health in an interview after reading the published paper.

“Some people rely on their work to decide once again that mammography will attack the Canadian National Breast Screening Study because they have not found the benefits of mammography.”

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He added that CNBSS is the only breast screening study in the world that was able to collect risk factors for breast cancer in all women who participated. He said the commentary would “confuse” the masses.

“I don’t think mammography screening is beneficial,” he said.

“Mammography is a great tool for diagnosing women when they have a reason to worry about their breasts, and that’s the way it should be used as a diagnostic tool.”

Mammograms can be used for screening to do “all sorts of peculiar things,” such as detecting lesions that haven’t progressed to harmful ones, he said. Ultimately, they can lead to potentially dangerous “overtreatment”.


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Concerns about the results of the study and its randomization have been reported for years.

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However, in 1997, an external investigation into the study “could not reveal credible evidence” that the random assignment of women in court was somehow “destroyed.” According to the report, the destruction, if any, was minimal and “may have had a minor impact” on the findings.

In 2019, the Canadian National Breast Screening Study was selected as one of the Top Five Research Papers of the British Medical Journal for 10 years.

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Susan Kinghorn, a medical radiologist who worked on CNBSS, said she was given a list of 10 or 12 study participants at the beginning of the day when she was supposed to receive the mammogram.

Based on a list of 20 to 24 females in all, they were supposed to be random, she told Global News, but sometimes the names of the females on her original list are of physical breast examinations. Will change later.

“I was told I shouldn’t doubt it, I was just going to do it. Smith had to have a mammogram,” she said. “Suppose Mrs. Jones was on the list. That same day she was removed from the list and Mrs. Smith replaced her.”

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Kinghorn always had a total of 10 to 12 names and didn’t “sound exactly”, but she said she was a new graduate and was grateful for her work. When she asked, she said her concerns were dismissed and what really matters was that the patient was “checked out.”

In the end, Kinghorn completed only four to five weeks of the three-month contract for pilot studies.


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Currently, the Canadian Task Force on Preventive Medicine does not recommend regular mammograms unless women between the ages of 40 and 49 have an existing condition or a higher risk than average.

The Canadian Cancer Society recommends that women in that age group consult their doctor about the benefits of mammograms and advises women aged 50-74 to get mammograms every two years.

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The impact of research on policy may have contributed to the avoidable deaths of more than 400 Canadian women each year, Yaffe said.

“Screening saves lives,” said co-author Dr. Jean Seeley, head of breast imaging at Ottawa Hospital. “If localized breast cancer is detected early, the 5-year survival rate is 98%.”

© 2021 Global News, a division of Corus Entertainment Inc.



Researchers say the studies that shaped the Canadian breast cancer screening guidelines are “defective.”

Source link Researchers say the studies that shaped the Canadian breast cancer screening guidelines are “defective.”

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