Practice Patterns and Outcomes of Novel Targeted Agents for the Treatment of ERBB2 -Positive Metastatic Breast Cancer

Abstract

Importance: Clinical trials have shown that the addition of pertuzumab to trastuzumab-based chemotherapy for first-line treatment of ERBB2-positive metastatic breast cancer is associated with considerable improvement in overall survival (OS). In the second-line setting, trastuzumab emtansine (T-DM1) improves OS compared with capecitabine/lapatinib in patients previously treated with trastuzumab-based chemotherapy. However, there are few data describing long-term real-world outcomes with these agents. Objective: To describe practice patterns and outcomes associated with pertuzumab and T-DM1 in routine clinical practice. Design, Setting, and Participants: This population-based retrospective cohort study used the Ontario Cancer Registry linked to electronic treatment databases to identify all patients treated with pertuzumab and T-DM1 following reimbursement approval in Ontario, Canada, which has a single-payer public health system. Participants included women with stage IV ERBB2-positive metastatic breast cancer receiving treatment with pertuzumab for first-line metastatic indication from December 2013 through December 2017, and those treated with T-DM1 from May 2014 through December 2017. Pertuzumab and T-DM1 cohorts were analyzed separately. Data were analyzed December 2019 to December 2020. Exposures: Treatment with pertuzumab or T-DM1. Main Outcomes and Measures: The primary outcome was OS, determined using the Kaplan-Meier method. Factors associated with OS were identified using a Cox proportional hazard model. Results: The median (interquartile range [IQR]) age of the 795 women who received pertuzumab and 506 women who received T-DM1 was 57 (49-67) and 56 (48-66) years, respectively. Among the cohort of patients who received pertuzumab, the median (IQR) OS and time on treatment was 43 (16.2-unavailable) and 14 (6.0-26.2) months, respectively. In the T-DM1 cohort, the proportion of pertuzumab-naive patients decreased over time from 68 of 91 [74.7%] in 2014 to 16 of 89 [18.0%] in 2017 (P