TORONTO – A new paper questions the science behind the Canada National Breast Cancer Screening Study (CNBSS) from the 1980s, a controversial study that has divided researchers in many years.
Researchers from Toronto’s Sunnybrook Research Institute, Ottawa Hospital, the University of British Columbia, the University of Alberta and Harvard Medical School published the results of their test of CNBSS in the Journal of Medical Examination this week, Alleged that the original study had significant flaws, particularly in the randomized aspect of the study.
The CNBSS was a series of trials conducted in the 1980s at 15 screening centers in six provinces: Nova Scotia, Quebec, Ontario, Manitoba, Alberta and British Columbia. Nearly 90,000 women between the ages of 40 and 59 took part in the study.
Its purpose was to determine if cancer screening programs were helping to save women’s lives, and to assign participants to two groups – one group consisted of women aged 40 to 49 and 50 to 59. mammogram and another control group, where both age groups had a single physical exam.
All participants were followed by the study for several years.
During the 5-year screening period, CNBSS found that 666 cases of invasive breast cancer were diagnosed in the group that received mammograms and 524 cases were diagnosed in the control group that received physical exams. Of those diagnosed, 180 women in the mammogram group and 171 women in the control group died of breast cancer during 25 years of follow-up.
The overall risk of dying from breast cancer diagnosed during the screening period and the cumulative mortality from breast cancer were similar between the women in the mammogram group and those who did not. women in the control group, CNBSS found.
The researchers then determined from that data that mammograms for women ages 40 to 49 did not reduce breast cancer death rates for women at average risk of the disease.
The CNBSS findings have influenced healthcare policy and guidance about when women can participate in screening programs, with guidelines from the Canadian Task Force on Preventive Health Care. (CTFPHC) currently does not recommend screening for breast cancer with mammograms for women aged 40 to 49 if they do not have any pre-existing factors, such as a direct family member with breast cancer. breast cancer or the BRCA gene.
In a statement emailed to CTVNews.ca on Tuesday, CTFPHC co-chair Dr Brenda Wilson said the organization “conducts a detailed and rigorous evidence review to develop guidance. Our guidelines, including those on breast cancer screening, are recognized as the best in the world… One reason for this is the careful and detailed process that the Task Force uses. used to weigh the evidence, available in their documentation. ”
When asked if the CTFPHC would review the guidelines outlined by the new paper, the statement said, “The Task Force integrates the best available evidence into its guidelines. When there are fundamental changes to that evidence, the Task Force updates its full review of the evidence body, including any new evidence. We do not comment on individual studies or opinion pieces without going through that process.”
RESEARCH PERSON TO SHARE
One of the co-authors of the new paper, radiologist Dr Jean Seely, head of breast imaging at the Ottawa Hospital, told CTVNews.ca in a phone interview on Tuesday. that experts around the world have “long suspected” that there are problems with the science of CNBSS.
“Surname [the CNBSS] are the only randomized controlled trials out of eight showing no benefit from screening mammography,” she said. “A lot of questions have been raised over the years [which] suggests that there may have been a problem with the randomization process, which allowed more women with clinically advanced cancer to be assigned to the study’s screening group. “
Seely says those doubts are what prompted her and her fellow researchers to examine the central nervous system more closely, and during the investigation, they determined that the trial participants were clinical breast examination before being assigned to one of the two experimental groups.
The new paper suggests that breast screening affects whether women are included in the control group or the group that gets mammogram screening.
“We have very credible eyewitness testimony that shows it happened in two different locations,” Seely said. “The basic evidence is that – with the best of intentions – the nurses who examined the women allotted them to the mammogram arm with the intention of getting their attention.”
The study’s lead author Dr. Martin Yaffe of the Sunnybrook Research Institute echoed Seely’s concerns.
“Our study revealed a number of protocol violations in the CNBSS related to how patients were randomly assigned to experimental groups – whether or not to have their breasts examined,” Yaffe said. “Given these important issues, the trial results are unreliable and should not be used to inform breast cancer screening policies.”
The paper’s authors argue that CNBSS should not provide screening guidance because of “broken randomization,” according to Seely.
“We now know that many women with symptomatic breast cancer have been recruited… so there really shouldn’t be an announcement of screening guidelines today,” says Seely, adding that learned that the quality of mammograms was poor during the trial period.
Seely says she’s “surprised” that the alleged data corruption could have happened and the study still published.
“I am also concerned when we have convincing evidence that this has happened… I think as a Canadian, I feel a bit embarrassed or ashamed,” she 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 get screened.”
However, Dr Cornelia Baines, professor emeritus at the University of Toronto’s Dalla Lana School of Public Health who has worked on CNBSS, categorically denied the evidence of the new papers in an email and phone conversation with CTVNews.ca.
Baines wrote in an email: “Speculation and anonymous comments are not proof. “The JMS article shows that women aged 40-49 seek screening mammograms in CNBSS because of symptoms. In fact, women have access to diagnostic mammograms regardless of age already in our universal health care system. Unlike the US, Canadian women do not need to seek free care in research trials.”
“Nurses do not need to preclude the randomization process because of a positive clinical outcome,” she continued. “A positive test requires a referral to the study surgeon, who is completely free to request a diagnostic mammogram.”
Baines says that screening center coordinators are independent of examiners and there are only four criteria for admission to CNBSS: the woman’s age, the woman is not pregnant, has no history of breast cancer, and they have not had it. sick. mammogram in the 12 months prior to the study.
“We expect women to be honest and almost all of them are,” she wrote. “In 2019, the BMJ rated our 2014 paper on CNBSS’s 25-year results as one of the five best papers it has published in the decade.”
“I’ll be brief – the radiologists themselves don’t like our study [and] Baines said in a phone conversation with CTVNews.ca
Currently, there is no universal breast cancer screening program nationwide. A woman in her 40s in BC can be screened for breast cancer, as a woman of the same age in Nova Scotia. However, in Ontario, a woman needs a referral from her GP.
The authors of the new paper argue that any woman in her 40s should get screened to detect the disease more quickly.
For law professor Jennifer Quaid, early screening is something she often thinks about after experiencing breast cancer.
“I got great care and treatment…but what pisses me off is that it’s preventable. I think it should have been picked up earlier,” the University of Ottawa professor said in a phone interview with CTVNews.ca on Tuesday.
Quaid, now in her 50s, discovered a small lump in November 2019 but paused seeing her doctor due to work needs and the subsequent COVID-19 pandemic, making in-person visits to her clinic. Doctors are often delayed or discouraged. In the summer of 2020, she saw the doctor who ordered a mammogram for her.
“Technology came back and said ‘the radiologist wants to have a quick chat with you,’ at which point I knew something was wrong,” says Quaid. She was eventually diagnosed with cancer. Stage three breast cancer requires a total mastectomy and total lymph node reduction.
“I just had a very successful vacation where I got every grant I applied for and wrote some pretty important papers,” says Quaid. “So I felt like I was getting ready to warm up and suddenly it was like someone just pulled the floor away from you. That was probably the worst moment.”
Quaid had surgery and underwent chemotherapy followed by radiation until mid-March 2021.
“I don’t want to be blamed,” she said. “You know, people do the best they can. But my doctor knows that… I have breast cancer in the family, but not my mother, and I have no sisters and my grandmother does not have breast cancer. So, under the Ontario rules, I’m not eligible [for screening]. ”
Quaid wanted to screen women for breast cancer earlier, because analysis of tumors removed from her body during surgery showed they had been there for at least one to two years.
“I will never be able to go back to exactly how I was before,” she said. “I also lost a productive year at the top of my career and I will never get it back. So if I can stop another person from going through that, it’s worth it. ”