Survival outcomes for Australian women receiving trastuzumab for HER2-positive metastatic breast cancer following (neo)adjuvant trastuzumab: a national population-based observational study (2006–2014)

BACKGROUND: Patients treated with (neo)adjuvant trastuzumab who relapse and receive trastuzumab for metastatic breast cancer (MBC) are a growing population with little outcome data given their exclusion from most clinical trials. We aim to estimate survival outcomes for this trastuzumab ‘pre-treated’ population. METHODS: Population-based study of Australian women receiving trastuzumab for HER2-positive MBC between 2006 and 2014, who also received (neo)adjuvant trastuzumab. We used Kaplan–Meier methods to estimate the following: overall survival (OS) from initiation of trastuzumab for MBC; duration of trastuzumab for MBC; and time from last (neo)adjuvant trastuzumab to first trastuzumab for MBC. RESULTS: Of 3199 patients dispensed trastuzumab for MBC, 634 (20%) had received (neo)adjuvant traztuzumab. Pre-treated patients had a median (interquartile range) OS of 21.8 months (10.9–51.6), trastuzumab duration of 12.8 months (4.7–17.5), and time from last (neo)adjuvant trastuzumab to first trastuzumab for MBC of 15.6 months (6.5–28.6). Median OS for patients initiating trastuzumab <12 months and ⩾12 months from their last (neo)adjuvant trastuzumab were 17.1 months and 24.8 months, respectively. CONCLUSIONS: Patients starting trastuzumab for MBC following (neo)adjuvant trastuzumab had a median treatment duration of 1 year and OS of almost 2 years. These data help inform clinical practice and service planning for this under-researched population.