in a paper published just two weeks ago in the journal of medical screening, researchers say the canadian national breast screening study (cnbss), which has been the basis of national breast cancer screening guidelines and long been considered a valuable and esteemed mammogram study, is packed with fateful flaws.
the study was based on two trials conducted in the 1980s, involving 90,000 participants between the ages of 40 and 59; 50,000 in the 40 to 49-year-old group and 40,000 women aged 50 to 59. each was supposed to be randomly assigned to either a control group or a study group.
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jennie dale, executive director of dense breasts canada , which is a group of breast cancer survivors and health professionals dedicated to raising awareness about the risks of dense breasts, says that cancer experts have been aware of the study’s flaws for three decades — but no one would listen.
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“we hear from women in their 40s who have been denied mammograms and later discover they have late stage breast cancer, which stems back to this study,” says dale, whose organization surveyed 2500 canadian women, 11 per cent of whom said they have been denied a mammogram in their 40s. “we’re trying to get the word out and to get the government to act responsibly, because this is criminal and women are dying needlessly.”
the public health agency of canada did release a statement in late november saying the task force is “arms-length from the government” and, therefore, “it would be inappropriate for phac to direct the task force on which studies to include or not include in their guidelines.” in other words, they admit little responsibility.
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meanwhile, the canadian cancer society’s dr. stuart edmonds, executive vice-president of mission, research and advocacy, said in a statement that the task force’s guidelines are based on far more evidence than just the one study, and does take into consideration advanced technologies.
in a similar statement, mj decoteau, founder and executive director of rethink breast cancer , said they, along with the canadian cancer society and the canadian breast cancer network , will be conducting an independent real-world evidence review to “clear any confusion on this issue,” and to build understanding of the impact and effectiveness of screening guidelines.
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a lack of expertise
with a breast cancer expert on the task force, it seems obvious that there will be less women in quaid’s position moving forward. but how was such an expert left out of a task force expressly focused on breast cancer?
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in other parts of the world, experts are included, and potential conflicts are managed. for example, the guidelines international network (gin), an berlin-based organization that develops clinical practice guidelines, involves experts, requiring them to formally declare potential conflicts of interest which are then evaluated on whether these conflicts create a legitimate concern or not.
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