Breast cancer is the most commonly diagnosed cancer and the second most common cause of cancer-related death among women in Ontario.1 More than 10 000 cases are diagnosed each year in the province.1 Several molecular subtypes of breast cancer have been identified b ased o n h ormone receptor and human epidermal growth factor receptor 2 (HER2) status.2 These molecular subtypes have been shown to affect survival: patients with hormone-receptor-negative tumours tend have greater mortality and lower survival than those with hormone-receptor-positive tumours. [3][4][5] Although the relation between breast cancer molecular subtype and survival has been studied in other jurisdictions, including British Columbia, 6,7 limited information is available for Ontario. The goal of this study was to determine how breast cancer molecular subtype affects survival among Ontario women and how survival for each subtype varies by selected demographic and tumour-based characteristics.
Methods
Setting and study populationThe study population included all cases of malignant breast cancer diagnosed in girls and women aged 15 years or more in Ontario between Jan. 1, 2010, and Dec. 31, 2012. We chose this period because data on molecular subtype were unavailable for cases diagnosed before 2010, and mortality data were unavailable for cases diagnosed after 2012. The relation between breast cancer molecular subtype and survival has been studied in several jurisdictions, but limited information is available for Ontario. The aim of this study was to determine breast cancer survival by molecular subtype and to assess the effect on survival of selected demographic and tumour-based characteristics.