TORONTO — A new paper questions the scientific process behind the Canadian National Breast Cancer Screening Study (CNBSS) from the 1980s, a controversial study that has divided researchers for years.

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Researchers from Toronto’s Sunnybrook Research Institute, Ottawa Hospital, University of British Columbia, University of Alberta and Harvard Medical School Published its examination of CNBSS in Journal of Medical Screening This week, it alleged that the original study had significant flaws, particularly in the randomization aspect of the research.

NS CNBSS was a series of tests In the 1980s, 15 screening centers were carried out in six provinces: Nova Scotia, Quebec, Ontario, Manitoba, Alberta and British Columbia. 90,000 women aged 40 to 59 participated in the study.


It aimed to determine whether cancer screening programs helped save women’s lives, and assigned participants into two groups – one with women ages 40 to 49 and 50 to 59 who received mammograms and the other a control group. Where both age sets had the same physical test.

All participants were studied for several years.

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Over the five-year screening period, the CNBSS found that 666 invasive breast cancers were diagnosed in the group that received the mammogram and 524 were diagnosed in the control group that received a physical exam. Of those diagnosed, 180 women in the mammography group and 171 women in the control group died of breast cancer during a follow-up period of 25 years.

The overall risk ratio for death from breast cancer diagnosed during the screening period and the cumulative mortality from breast cancer were similar between women in the group who received a mammogram and in the control group, the CNBSS found.

Researchers then determined from that data that mammograms for women ages 40 to 49 did not reduce mortality from breast cancer for women at average risk of the disease.

The CNBSS findings have influenced health care policy and guidelines for when women should be able to participate in screening programs, Canadian Task Force on Preventive Health Care (CTFPHC) Guidelines Breast cancer screening with mammograms is not currently recommended for women aged 40 to 49 if they do not have any pre-existing factors, such as a direct family member known to have breast cancer or the BRCA gene. Was.

In an emailed statement Tuesday to, CTFPHC co-chair Dr. Brenda Wilson said the organization “conducts rigorous, detailed evidence review to formulate guidelines for our guidelines, including breast cancer screening.” is recognized as the best in the world… Part of the reason is that the task force uses a careful and detailed process to weigh the evidence, which is available in its guideline documentation.”

When asked whether the CTFPHC would revisit the said guidelines in light of the new paper’s allegations, the statement said, “The task force integrates the best available evidence into its guidelines. When there are significant changes to that evidence.” , then the task force updates its full review of the body of evidence, including any new evidence. We do not comment on individual studies or opinion pieces without going through that process.”

Researchers divided

One of the new paper’s co-authors, radiologist Dr. Gene Seeley, who heads breast imaging at Ottawa Hospital, told in a telephone interview Tuesday that experts around the world have “long-held suspicions”. Was that there were issues with the science of CNBSS.

“They [the CNBSS] These were the only randomized controlled studies out of eight to show no benefit from screening mammography,” she said. “A lot of questions have been raised over the years.” [which] Turns out there was probably a problem with the randomization process, which allowed more women with clinically advanced cancer to be allocated to the screening arm of the study.

Seely says that those doubts prompted him and his fellow researchers to examine the CNBSS more closely, and in the process of their investigation determined that the trial participants had no choice but to be assigned to one of two test groups. Had a clinical breast exam before.

The new paper shows that breast exams influenced whether women were placed in the control group or the group to receive mammogram screening.

“We have very reliable eyewitness testimony showing that this happened at two different sites,” Seely said. “The ground evidence is that – with the best of intentions – the nurses who examined the women were allocating them to the mammography branch with the intention of getting their attention.”

Lead study author Dr Martin Yaffe of the Sunnybrook Research Institute echoed Seeley’s concerns.

“Our research reveals several protocol violations within the CNBSS in terms of how patients were randomized into trial groups – whether or not to receive breast screening,” Yaffe said in a release. “Given these important issues, test results are unreliable and should not be used to inform policies on breast cancer screening.”

The paper’s authors argue that CNBSS should not inform screening guidelines because of “corruption of the randomization process,” according to Seeley.

Seeley said, “We now know that women who had symptomatic breast cancer were actually recruited …

Seely says she was “surprised” that there might have been alleged data corruption and that the study was still published.

“It’s also disturbing to me that we have strong evidence of this. I think being a Canadian I felt a little embarrassed or ashamed,” he said. “I think the bottom line is that women shouldn’t be hurt by this and they should be empowered to have good health and be screened.”

However, Professor Emerita in the Dalla Lana School of Public Health at the University of Toronto, Dr. Cornelia Baines, who worked on CNBSS, explicitly denied the evidence in the new papers in an email and telephone conversation with

“Speculation and anonymous comments do not constitute evidence,” Baines wrote in an email. “The JMS article suggests that women aged 40-49 were seeking screening mammograms at CNBSS because of symptoms. In fact our universal health care system had women’s access to diagnostic mammograms, regardless of age. America In contrast, Canadian women do not require free care in research trials.”

“Nurse examiners were not required to fail the randomization protocol because of a positive clinical test,” she continued. “A positive test required a referral to the study’s surgeon, who was completely free to order a diagnostic mammogram.”

Baines says the screening center coordinators were independent of the examiners, and there were only four criteria for admission to the CNBSS: a woman’s age, that the women were not pregnant, had no history of breast cancer, and had not had 12 from the study. A mammogram a month ago.

“We expected women to be honest and virtually everyone was,” she wrote. “In 2019, the BMJ rated our 2014 paper on the CNBSS 25-Year Outcomes as one of the five best published in the decade.”

“I will tell you briefly – it is radiologists who do not like our study” [and] Carrying it forward for three decades, you would be surprised that even 30 years after such attacks, the CNBSS is still highly respected by people other than radiologists,” Baines said in a telephone conversation with CTVnews.

human cost

Currently, there is no universal breast cancer screening program across the country. In BC a woman in her 40s can get screened for breast cancer, as can a woman in the same age group in Nova Scotia. In Ontario however, a woman needs a referral from her family doctor.

The authors of the new paper argue that screening should be available for any woman in her 40s to catch potential disease early.

For law professor Jennifer Quaid, early screening is something she often thinks about after her experience with breast cancer.

“I received excellent care and treatment… but what annoys me is that it could have been prevented. I think it should have been raised earlier,” the University of Ottawa professor told on Tuesday. Said in a telephone interview with.

Quaid, now in his 50s, found a small lump in November 2019, but stopped seeing his doctor because of the demands of his career and the subsequent COVID-19 pandemic, where in-person visits to the doctor’s office took place. was often delayed or discouraged. In the summer of 2020, she saw her doctor, who ordered a mammogram for her.

“The tech came back and said ‘the radiologist wants to have a quick chat with you,’ at which point I knew something was wrong,” Quaid said. She was diagnosed with stage three breast cancer that required a complete mastectomy and a complete lymph node reduction.

“I just came out of a very successful sabbatical where I got every grant I applied for and wrote some important papers,” Quaid said. “So I felt like I was ready to launch and suddenly it felt like someone pulled the floor off from under you. That was probably the worst moment.”

Quaid had surgery, and went through chemotherapy, then radiation, until mid-March 2021.

“I don’t want to feel like I’m blaming,” she said. “You know, people do the best they can. But my GP knew that … I have breast cancer in my family, but I don’t have a mother, and I don’t have a sister and my grandmother has breast cancer.” Didn’t have cancer. So I didn’t qualify under Ontario rules [for screening],

Quaid wants women to be screened for breast cancer first, as analysis on tumors removed from her body during surgery…