A Population-Based Analysis of Breast Cancer Incidence and Survival by Subtype in Ontario Women

Background: Breast cancer (bca) is the type of cancer most frequently diagnosed among women in Canada. Breast cancer is categorized into various molecular subtypes by the expression of estrogen receptor (er), progesterone receptor (pgr), and her2 (human epidermal growth factor receptor 2). Currently, Canada has no national cancer registry with epidemiology data by subtype. Thus, we conducted a study to determine incidence, survival, and clinicopathologic characteristics by bca subtype [triple negative breast cancer (tnbc); her2+; and hormone receptor–positive (hr+), her2–] in Canadian women newly diagnosed with bca. Methods: Female patients diagnosed between 1 April 2012 and 31 March 2016 (fiscal 2012–2015) were identified in the Ontario Cancer Registry, and individual patient data were linked to data in provincial health administrative databases. Descriptive statistics and Kaplan–Meier curves were generated. Results: In this cohort, 3277 women (9.5%) had tnbc, 4902 (14.3%) had her2+ bca, and 22,247 (64.8%) had hr+, her2–breast cancer. The annual incidence was 15 per 100,000 for the tnbc group, 21–23 per 100,000 for the her2+ group, and 97–105 per 100,000 for the hr+, her2– group. The lowest median overall survival (mos) of 8.9 months was observed in women with clinical stage iv tnbc. In comparison, the mos was 37.3 months in those with her2+ disease and 35.2 months in those with and hr+, her2– metastatic bca. Conclusions: In the present study, the most recent and largest administrative database analysis of a Canadian population to date, we observed a subtype distribution consistent with previously reported data, together with comparable annual incidence and overall survival patterns.