48 Clinicopathological Outcomes and Biomarker Shifting of Breast Cancer Brain Metastases

Brain Cancer Canada Travel Award Recipient INTRODUCTION Breast cancer brain metastases (BCBMs) are associated with a poor prognosis. The project aims are to characterize the clinicopathological outcomes of patients with BCBMs at LHSC and compare biomarker profiles between primary tumor and BM. Methods Patients who had BCBMs surgically-resected or biopsied at LHSC were identified. Retrospective chart review was conducted. Kaplan-Meier curves were generated and Cox-regression analyses were conducted to determine clinical outcome predictors. RESULTS Seventy-five female patients were identified. Mean age at BCBM diagnosis was 56.1 years and mean time to developing BCBM was 5.4 years (range: 0-23.0 years). Triple-negative (18/75, 24.0%) and HER2+ (14/75, 18.7%) were the most common subtypes. Median OS after BCBM diagnoses was 2.4 years. Solitary BCBM (p=0.0276) and no extracranial systemic disease (p=0.0276) were associated with longer OS after BCBM diagnosis. 51 patients had paired immunohistochemistry (IHC) markers of their primary BC and BMs. 11/51 (21.6%) patients exhibited a subtype switch with hormone receptor loss (5/11, 55.6%) being the most common change. Triple-negative subtype, multiple BMs, presence of neurological deficits, tumor >3 cm, and hydrocephalus were negative prognostic factors. After multivariate Cox-regression, however, only triple-negative subtype and multiple BMs remained significant. Subtype switching did not appear to impact OS (p=0.34). CONCLUSIONS The management of BCBM remains challenging with survival remaining poor. Within our cohort, a noticeable proportion of patients exhibited biomarker profile shifting between the primary BC and BCBM. This may have clinical implications and further investigations are required to understand its mechanisms and impact on treatments.