Thousands of Canadian women in their 40s may have died needlessly from breast cancer due to a lack of access to mammographies as a result of two “skewed” studies that informed guidelines recommending against screening for this age group, a team of researchers says.
In a commentary published in the Journal of Medical Screening on Nov. 23, researchers from five universities said they have new evidence that the Canadian National Breast Screening Study trials conducted in the 1980s were not randomized properly, leading to unreliable results.
Results at the time found that routine mammograms did not reduce deaths in women aged 40 to 49. A second trial involving women from 50 to 59 was also carried out with similar results.
The researchers from the University of Toronto, University of Ottawa, University of British Columbia, University of Alberta, and Harvard Medical School said they are concerned about “serious errors in trial design and conduct” and therefore the studies “should not influence breast screening policies.”
“The bottom line for Canadian women is that this study suppressed screening, especially for women 40-49, for decades and likely indirectly resulted in a lot of lives lost,” they wrote.
“The study’s influence on policy has had a substantial impact on breast cancer outcomes in Canada and may have contributed to the avoidable deaths of over 400 Canadian women each year.”
‘Major Flaws’ Introduced in Trial
Sheila Appavoo, co-author of the commentary and associate clinical professor in the University of Alberta’s (U of A) Faculty of Medicine & Dentistry, said two “major flaws” were introduced during the trial for the 40 to 49 age group.
First, the female volunteers were given clinical breast examinations by expert nurses before being placed into supposedly randomized groups for either mammography or no screening, noted Appavoo in an article in the U of A’s Folio publication on Nov. 23.
However, due to the limited access to mammography outside of the trial, the study staff “put more symptomatic women with lumps or pain into the mammography group than in the control group.”
Secondly, in cases where screening centres had difficulty finding enough volunteers, women were recruited from breast surgeons’ offices, making the probability of having asymptomatic women in the study very low.
“That’s why the study results showed you had more of a risk of dying if you had been screened than if you hadn’t been screened,” Appavoo said.
Due to the trial results, she said the Canadian Task Force on Preventive Health Care (Task Force) recommends routine mammography starting at age 50.
“Because the Canadian guidelines recommend not screening until 50, a lot of women are denied that requisition,” she said.
To date, the Task Force’s website states that for women aged 40 to 49 they recommend “not screening with mammography.”
“The decision to undergo screening is conditional on the relative value a woman places on possible benefits and harms from screening,” it says.
As for those who still wish to be screened, it says “care providers should engage in shared decision-making with women who express an interest in being screened.”
In their commentary, the researchers said the “subversion of randomization” and the “inclusion of many symptomatic women in a screening trial” were also built into the study for women aged between 50 and 59, skewing the results.
In an email statement to The Epoch Times, Dr. Brenda Wilson, co-chair of the Canadian Task Force on Preventive Health Care, said the Task Force integrates “the best available evidence into its guidelines” and that the recommendation to screen with mammography at age 50 is “conditional.”
“[The Task Force] does not strongly advise against screening, rather it advises health professionals and women to discuss the option and reach a decision that works for the individual,” wrote Wilson.
“When there are substantive changes to that evidence, the Task Force updates a full review of the body of evidence, including any new evidence.”
The researchers, on the other hand, said they have “direct eyewitness evidence” of the “flaws” in the studies, arguing the trials “were not reliably randomized controlled trials, nor were they truly trials of screening.”
“Their results should no longer be used in meta-analyses of screening nor to inform policies on breast cancer screening,” they said.