The Canadian National Breast Screening Study. Why? What next? And so what?

Why the National Breast Screening Study (NBSS)? In 1979, after reviewing the Breast Cancer Detection Demonstration Projects (BCDDP), the Beahrs Working Group made 11 recommendations. The NBSS protocol reflected a number of these recommendations, particularly the evaluation of screening women age 40-49 and the still unanswered question of the incremental benefit of mammography versus physical examination of the breasts among women age 50-59. Three years after publication of NBSS's 7-year results and in light of other published evidence from screening trials (as opposed to observational studies), it is reasonable to recommend screening with mammography and physical examination every 2 years for women age 50-59. In contrast, it is not reasonable to offer screening mammography to women age 40-49 other than in the context of a controlled trial, an opportunity currently available in the United Kingdom. The Beahrs recommendation, that "physical examinations should be continued in the Breast Cancer Detection Demonstration Projects as a routine screening modality for all ages," remains justifiable as long as so many women age 40-49 are having mammograms performed, given the relatively poor sensitivity of mammography in this age group. Criticism of the NBSS, mainly by radiologists, will continue until the NBSS yields results that support its critics' belief in the efficacy of screening. To date, responses to critics of the NBSS have focused on correcting misinformation and clarifying NBSS procedures. Useful critical commentary should await the results of a 10-year NBSS follow-up and the U.S. National Cancer Institute-sponsored meta-analysis of screening trials. Rigorous critical scrutiny should be directed at all trials.