Real-world treatment patterns and associated outcomes in patients with HER2-positive unresectable or metastatic breast cancer: the HER2 REAL Study.

BACKGROUND: The HER2 REAL (NCT04857619) retrospective study explored treatment practices and survival outcomes in patients with human epidermal growth factor receptor 2 (HER2)-positive unresectable breast cancer/metastatic breast cancer (mBC) in routine clinical care across six countries. METHODS: Adult patients (≥18 years) diagnosed with HER2-positive mBC, having ≥12 months of follow-up data from diagnosis and completing one or more line of therapy (LOT) were enrolled. The primary endpoint was treatment patterns. Secondary endpoints included clinicodemographic characteristics and survival outcomes using the Kaplan-Meier method and presented as median [95% confidence interval (CI)]. Data for the first two LOTs in the metastatic setting are presented. RESULTS: Of the 763 patients enrolled, 684 patients were analyzed for baseline characteristics. Majority [99.6% (681/684)] were women, 67.3% (379/563) were postmenopausal with median (range) age of 55 (20-91) years. At index date, 99.3% (597/601) of patients had stage IV disease, and 72.1% (465/645) reported visceral metastases. Immunohistochemistry score was available for 64.6% of patients. Median (range) study follow-up was 30.1 (1-167) months. A total of 96.1% (n = 657) and 84.5% (n = 578) of the patients had data on LOT1 and LOT2, available in the medical records. In LOT1, trastuzumab (TRA)+pertuzumab (PTZ)+chemotherapy (CT)-based regimen were prescribed to 58.1% and non-TRA+PTZ+CT-based to 41.6%; TRA+CT-based regimen to 20.2%, which is a subset of the TRA+PTZ+CT group. In LOT2, trastuzumab emtansine (T-DM1)-based regimen was prescribed to 45.5% and non-T-DM1-based, and TRA+CT-based to 53.1% and 11.8% patients, respectively. The median (95% CI) real-world overall survival (rwOS) was 41.4 (38.1-45.8) months for overall cohort. In LOT1, median rwOS was 46.8 (38.7-50.7) months for TRA+PTZ+CT-based regimens. In LOT2, median rwOS was 23.9 (20.5-29.5) months in the T-DM1 cohort. Disease progression or death and toxicity were major reasons for treatment discontinuation. CONCLUSIONS: This retrospective study shows heterogeneity in treatment patterns and survival outcomes in real-world patients with HER2-positive mBC, indicating the need for optimization of treatment in patients with HER2-positive mBC in real-world.