Grant: Operating Grant: Data Analysis Using Existing Databases and Cohorts

Until recently, women diagnosed with a type of breast cancer which is positive for the HER2 receptor and has spread to other parts of their body were initially treated with chemotherapy and an antibody called trastuzumab. If their cancer progressed despite treatment, a combination of two drugs, capecitabine and lapatanib, was used. A recent study showed that adding the antibody pertuzumab to the combination of chemotherapy and trastuzumab prolongs life in these women, and has been used in Ontario since 2013. In those who progress, another clinical trial demonstrated that a drug named trastuzumab emtansine (T-DM1) is better than capecitabine/lapatinib. T-DM1 has been used in Ontario since 2014. However, treatments shown to prolong survival in clinical trials do not always lead to the same benefits when they are used in the "real world", and sometimes lead to more or different side effects than those seen in studies. Further, not all patients have equal access to new drugs due to reasons such as risk of side effects in certain patients, or lack of awareness of study results and available funding by physicians. This research is being done to determine if patients receiving treatment for breast cancer in Ontario are receiving equal and adequate access to these new drugs, and whether the risks and benefits of pertuzumab and T-DM1 are still important when used in patients not enrolled in clinical trials. In order to do this research, we will use data from large Ontario databases which have collected data on patients receiving treatment for HER2-positive breast cancer. We will analyze these data to examine the proportion and characteristics of patients who have received these drugs, and determine whether their long-term outcomes are better than those treated before these treatments were available.