EXPRESSION OF ANDROGEN RECEPTOR IN BREAST CANCER BRAIN METASTASES

Given availability of central nervous system (CNS)-penetrant systemic therapies that target the androgen receptor (AR), we evaluated the expression of the AR “target” in breast cancer brain metastases (BrM). METHODS: An established, retrospective cohort of 57 patients with metastatic breast cancer who underwent surgery for BrM at the Sunnybrook Odette Cancer Centre (SOCC) between 1999 and 2013 was studied. AR expression in BrM samples was assessed in triplicate using immunohistochemistry (IHC). AR positive status was defined as nuclear AR expression ≥10% in tumor-infiltrating cells as a percentage of tumor area using the SP107 antibody. RESULTS: The median age of patients was 52 years (range 32-85 years). 17 (30%) patients had hormone receptor positive (HR+) /HER2-negative, 28 (49%) had HER2+, and 12 (21%) had triple negative breast cancer (TNBC) BrM. The median expression of AR was 20% (CI 1.6-38.3%) and 32 of 57 (56%) BrM were AR positive based on a cut-point of ≥10%. A significantly smaller proportion of patients with TNBC had AR+ BrM (n=2/12, 17%), compared to patients with HR+/HER2-ve (n= 9/17, 53%) or HER2+ (n=21/28, 75%) disease (p=0.04). Patients with AR positive versus AR negative BrM had similar overall survival (12.5 vs. 7.9 months, p= 0.6), brain-specific progression-free survival (8.0 vs. 5.1 months, p= 0.95), and time from breast cancer diagnosis to BrM diagnosis (51 vs. 29 months, p=0.16). CONCLUSION: AR is expressed in the majority of breast cancer BrM and represents a promising therapeutic target.