Temporal trends in breast cancer surgery in Ontario: can one randomized trial make a difference?

To assess the effect of a single randomized clinical trial, the National Surgical Adjuvant Breast Project (NSABP) B-06, on the surgical management of breast cancer in women. Retrospective cohort study. All hospitals in Ontario. A consecutive sample of 37,447 women with breast cancer newly diagnosed from Jan. 1, 1980, to Dec. 31, 1989, linked to a surgical procedure record in the Ontario Cancer Registry. The most invasive surgical procedure used within 90 days of diagnosis. Unilateral breast-ablative surgery (BAS) was performed in 57.3% of the women and breast-conserving surgery (BCS) in 31.6%. The annual rate of BAS declined from 77.5% in 1980 to 44.2% in 1989 and the rate of BCS rose from 12.5% in 1980 to 43.5% in 1989. The decline was linear from 1980 to 1984 and then accelerated significantly in 1985 (p < 0.0001), after the results of the NSABP B-06 trial were published. One randomized clinical trial can have an immediate and profound effect on medical practice.