RMTD-06 Treatment Patterns and Outcomes of Hr+/Her2- Breast Cancer With Brain Metastases: A Single-Center Retrospective Study

BACKGROUND Approximately 14% of patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (mBC) develop BrM during their lifetime, which is associated with a poor prognosis. We sought to assess the treatment patterns and outcomes of patients with HR+/HER2- breast cancer brain metastases (BCBrM). METHODS We conducted a single-centre retrospective cohort study of 204 patients (≥18 years of age) diagnosed with HR+/HER- mBC who were treated for BrM at the Sunnybrook Odette Cancer Centre between 2008 and 2018. We used descriptive statistics to summarize patient and treatment characteristics and Kaplan-Meier analyses for survival outcomes. The log-rank test was used to compare outcomes of patients with endocrine sensitive versus endocrine resistant disease. RESULTS Among 204 patients with HR+/HER2- BCBrM, the median age at BrM diagnosis was 56 years (range 31 – 93) and the median time between diagnosis of mBC to development of BrM was 15 months (interquartile range [IQR] 3 – 36 months). 135 (66.2%) patients had endocrine resistant disease, 53 (26%) patients had endocrine sensitive disease; endocrine sensitivity was not available for 16 patients (7.8%). The first line of systemic treatment following BrM diagnosis was chemotherapy for 46.1% of patients and endocrine therapy for 28.9% of patients. The median brain-specific (bs) progression-free survival (PFS) was 7 months (95% CI: 5.2 – 9) and median overall survival (OS) was 10 months (95% CI: 8.5 – 13.4). In subgroup analyses, bsPFS (5 months versus 11 months, p<0.001) and OS (7.3 versus 20.7 months, p<0.001) were significantly shorter among patients with endocrine resistant breast cancer than those with endocrine sensitive disease. CONCLUSIONS Patients with HR+/HER2- BCBrM have poor outcomes. A substantial proportion of patients with endocrine resistant disease have particularly short bsPFS and OS, highlighting the need for novel systemic treatment approaches with efficacy in the brain.