A critical appraisal of the Canadian National Breast Cancer Screening Study.

Point: Mammography Screening—Sticking to the Science

“…In his November 2014 article 9 , Dr. Steven Narod defended the cnbss, which has been heavily criticized by other scientists on the basis of methodologic flaws and poor mammography quality [10][11][12] .…”

“…In 1993, I was co-author on an article, which Narod unfortunately failed to cite, that laid out the criticisms of the cnbss without casting aspersions about the motives or underlying reasons for the deficiencies in that trial 10 . Because of the onslaught against screening mammography presented in the paper by Narod and the editorials by Baum 13 and Foulkes 14 , I thought that it would be useful to revisit the problems that caused the cnbss to stand apart from the other randomized controlled trials of breast cancer screening in being the only trial that concluded with a higher breast cancer death rate in the group invited to screening compared with the control group.…”

“…But, in the initial (prevalence) round of screening, women received a cbe before their names were entered, and there would therefore be some knowledge at the screening site of palpable abnormalities before the official registration of the participant occurred. Boyd et al 10,18 observed that, in the data presented in the first cnbss1 publication, of 24 women with poor-prognosis breast cancers discovered in the prevalence round, 19 were assigned to the study (mammography) arm and only 5 to the control arm. Of the 19 cancers in women assigned to the study arm, 17 were palpable, and so those cancers were not simply found earlier because of the lead time afforded by mammography.…”

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“…One of these, the CNBSS study, has been the subject of extensive criticism. 6 That said, mammography is far from perfect. Mammography lacks sensitivity; some cancers are missed.…”

Response to: “[Miller’s] Response to: ‘Beyond the Mammography Debate: A Moderate Perspective’”

“…In my response to Steven Narod's defense of the cnbss 3 , I pointed to the critical 1993 review of those studies by Boyd et al 4 , which raised multiple concerns regarding the conduct of the cnbss. Two of the most important were the apparent imbalance in advanced cancers found in the prevalence round of the cnbss and the poor diagnostic quality of the images as determined by at least 5 external expert breast radiologists who reviewed cnbss images 5 .…”