Canada follows the US in the rise of bilateral mastectomies for unilateral breast cancer: a 23-year population cohort study

Introduction The use of contralateral prophylactic mastectomy (CPM) continues to grow despite the absence of evidence supporting a survival benefit. This study's objectives were to (1) describe the trends in the rates of unilateral and bilateral mastectomy (BM) in women diagnosed with unilateral breast cancer (UBC) in Ontario, Canada from 1991 to 2013, and (2) identify factors associated with BM to treat UBC. Methods This retrospective cohort analysis included all women aged 18 and older diagnosed with UBC between January 1991 and December 2013. Health administrative data from the Institute for Clinical Evaluative Sciences, the Ontario Cancer Registry, and the Discharge Database were used to identify all breast cancer and mastectomy cases. Age-adjusted mastectomy rates were plotted over time. Univariable and multivariable analyses included clinically significant covariates. Results From 1991 to 2013 there were 172,165 cases of UBC and 64,886 mastectomies (37.7%) performed in Ontario. 13.6% of the mastectomies were bilateral. BM rates increased over sixfold (from 4 to 25%) across all age groups under age 70 over a 23-year period. On multivariable analysis, younger age, higher income, rural community, earlier breast cancer stage, lobular histology, availability of reconstruction and teaching hospitals were associated with increased odds of BM. Conclusions This is the largest population study of breast cancer patients in Canada and shows an increasing rate of BM for UBC. The results are similar to those already described in the US and highlight the importance of continued efforts to promote efficient communication and evidence-based decision-making prior to breast surgery.

Automated summary

This study examined trends in mastectomy rates for UBC patients in Ontario from 1991 to 2013, finding a sixfold increase in BM rates across all age groups under 70. Factors associated with increased odds of BM included younger age, higher income, rural community, earlier breast cancer stage, lobular histology, availability of reconstruction, and treatment at a teaching hospital.