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 Abstract 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.