186P A Real-World Study on Prevalence of and Outcomes Related to Brain Metastases among Patients with HER2-positive Metastatic Breast Cancer (Mbc)

Brain metastases (BM) are associated with poor prognosis and substantial morbidity and mortality among metastatic breast cancer (mBC) patients. There is limited real-world data on the prevalence of BM at metastatic diagnosis and across the metastatic treatment pathway. The goals of this study were to estimate the prevalence of BM among human epidermal growth factor receptor 2-positive (HER2+) mBC patients at mBC diagnosis and at start of each line of therapy (LOT), to describe the treatment patterns and to evaluate their overall survival (OS). Adult patients from the United States diagnosed with mBC from January 2013–May 2020 with biomarker results for HER2+ status were selected from the Flatiron Health electronic health record–derived database. Patients were followed from index date (date of mBC diagnosis) to death or last activity date. Descriptive statistics were used to describe baseline and clinical characteristics. OS was estimated using the Kaplan-Meier method. A total of 1,923 HER2+ mBC patients were included (mean age 60.4 years; 67.1% positive hormone receptor status [HR+]). The prevalence of BM at mBC diagnosis and by LOT are presented in the table. Patients with BM at mBC diagnosis (n=240) had a mean age of 55.3 years and 55.8% were HR+. The most common treatment in 1L and 2L were taxane/pertuzumab/trastuzumab (26.3%) and T-DM1 (30.4%), respectively. Median OS was 24 months for all HER2+ patients with BM and 37 months among those without BM at time of mBC diagnosis (Table).Table: 186PPrevalence of brain metastases and median OS in patients with HER2+ mBCIndex timepointPrevalence of BM% (95%CI)OS for patients with BM months (95%CI)OS for patients without BM months (95% CI)At mBC diagnosis, N = 1,92312.5 (11.0, 14.0)23.9 (18.5, 30.5)36.6 (33.9, 38.1)Start of 1L, N = 1,14711.2 (9.4, 13.1)25.5 (18.1, 33.8)35.4 (32.8, 37.7)Start of 2L, N = 64422.8 (19.6, 26.3)17.5 (14.5, 22.3)26.3 (24.0, 31.2)Start of 3L, N = 31233.0 (27.8, 38.5)14.1 (10.5, 17.5)19.4 (16.7, 24.0) Open table in a new tab Results from this real-world study of patients receiving care in community-based oncology clinics indicate that prevalence of BM in HER2+ mBC increases with number of prior lines of treatment and that survival is poorer in this population compared to those without BM.