174P Occurrence of brain metastasis and treatment patterns among patients with HER2-positive metastatic breast cancer

Abstract

The risk of brain metastasis (BM) is high (up to 50%) among patients diagnosed with HER2-positive (HER2+) metastatic breast cancer (MBC) compared with HER2-negative MBC. There are limited real-world data on the timing of BM development and subsequent treatment among such patients. The objective of this observational study was to assess BM occurrence and treatment among women with HER2+ MBC. Women ≥18 years old and diagnosed with HER2+ MBC between 6/1/2012 and 5/31/2018 were included in the study. Data were abstracted from electronic medical records from a network of community oncology practices maintained in the Vector Oncology Data Warehouse and included clinical and demographic characteristics, timing of BM diagnosis and treatment patterns. Of 372 study eligible patients, 165 (44.4%) had a record of BM. The majority of patients with BM were white (n=99; 60.0%) with a median age of 54 (range 29-83) years at MBC diagnosis. There were 82 patients (49.7%) with de novo MBC and 89 (53.9%) had hormone-receptor positive tumours. There were 37 patients (22.4%) with a record of BM at the time of initial MBC diagnosis (baseline), 63 (38.2%) developed BM during the first-line treatment, 23 (13.9%) during the second-line and 42 (25.5%) during the third-line or beyond. The median time to develop BM from initial MBC diagnosis was 12.5, 18.3 and 22.8 months, respectively. Post-BM systemic treatments varied. Among those with baseline BM (n=37), the most common regimens were trastuzumab plus pertuzumab along with taxane (n=13; 35.1%), trastuzumab monotherapy (n=3; 8.1%) and tamoxifen monotherapy (n=3; 8.1%). In patients who developed BM during follow-up (n=128), the most common regimens included pertuzumab plus trastuzumab (n=27; 21.1%), ado-trastuzumab emtansine monotherapy (n=13; 10.2%), and trastuzumab monotherapy (n=11; 8.6%). BM were common among patients with HER2+ MBC, and occurred at various points during the course of treatment. Post-BM systemic therapy varied widely, which may indicate a lack of standard of care for patients with HER2+ MBC after BM diagnosis and an unmet need in this patient population. Further analysis on treatment efficacy is required to understand whether treatment needs are met.