Alan Cassels, a pharmaceutical policy researcher, has weighed in on screening mammography (“Too many misled on breast-cancer screening,” May 21). He does women a disservice.
He quotes only the 25-year update of the Canadian National Breast Screening trial, and does not include the fact that this was the only trial of mammography screening that didn’t show decreased mortality. It is an outlier, and in 2002, the World Health Organization determined that it should be disregarded in future considerations of the benefit of mammography.
The flaws in the Canadian trial have been documented ad nauseam. But every five years, they publish an update and cause a media frenzy and confusion for women.
When the results of better trials are averaged, women invited to have mammography showed reduced death from breast cancer of 25 to 30 per cent. More important, in women who actually have mammograms (many women invited in trials do not, but are still counted in the mammogram group when deaths are counted) the mortality reduction is in the 40 to 50 per cent range.
But Cassels, whose declared conflict of interest is in selling his anti-screening book, says that promoting mammography is possibly dangerous. He quotes the harms of overdiagnosis and overtreatment, and cites Dr. Peter Gotschze and the Cochrane Review, which have been roundly criticized by authorities in public-health, epidemiology and statistics from all over the world because of their manipulation of data. Gotschze cherry-picked studies that supported his hypothesis and disregarded favourable studies, based on his misunderstanding of the methodology of cluster randomization in screening trials.
Mammography is not perfect. It doesn’t find all cancers, and when women are recalled when we find something on a mammogram that needs more tests, there is unavoidable transient anxiety and even sometimes a needle biopsy done with freezing to rule out cancer. But women know that this is reasonable, and would choose to have the test, rather than let a patronizing administration decide that they should be spared the anxiety and lose the opportunity to find a small cancer.
Canadians deserve to hear the truth, not Cassels slagging the Canadian Breast Cancer Foundation. They appear to have a better understanding of the science than he does. He should stick to his area of expertise.
Paula Gordon, MD, is a clinical professor at the University of British Columbia.
