Declining use of mastectomy for invasive breast cancer in Canada, 1981-2000

Objective: To evaluate the rate and magnitude of change in surgical practice for breast cancer in Canada in relation to publication dates of clinical trials and consensus conferences. Methods: Hospital separations with a diagnosis of invasive breast cancer were extracted from the Hospital Morbidity File from 1981 to 2000. Age-standardized rates of in-patient procedures for breast-conserving surgery and mastectomy were analyzed by province and age group and by geographic region. Results: In Canada, mastectomy rates decreased from 62.2 to 37.9 per 100,000 between 1981 and 2000; declines were largest between 1984 and 1985, following publication of the NSABP B-06 clinical trial in March 1985, and between 1991 and 1993, after the US NIH Consensus Conference in February 1991. Mastectomy rates plateaued between 1985 and 1991, and from 1993 to 2000; the transitory peak in 1988 corresponded to publicity surrounding Nancy Reagan's choice of mastectomy in 1987. Regional variations from the main pattern led to increasingly divergent mastectomy rates over time. Women aged 80+ were less likely to be treated by any surgery. Interpretation: Publication of clinical trial results and consensus conferences were associated with changes in surgical treatment for breast cancer in Canada. However, divergent mastectomy rates among Canadian regions point to inconsistent adoption of less invasive therapy despite a publicly-funded health care system and national consensus guidelines.