Clinicopathologic and Genomic Landscape of Breast Carcinoma Brain Metastases.

Abstract

BACKGROUND\nAmong breast carcinoma patients with metastatic disease, 15-30% will eventually develop brain metastases. We examined the genomic landscape of a large cohort of breast carcinoma brain metastases (BCBMs) and compared them to a cohort of primary breast carcinomas (BCs).\n\n\nMATERIAL AND METHODS\nWe retrospectively analyzed 733 BCBMs tested with comprehensive genomic profiling (CGP) and compared them to 10,772 primary breast carcinomas (not-paired) specimens. For a subset of 16 triple-negative breast carcinoma (TNBC)-brain metastasis (BM) samples, PD-L1 immunohistochemistry was performed concurrently.\n\n\nRESULTS\nA total of 733 consecutive BCBMs were analyzed. Compared to primary BCs, BCBMs were enriched for genomic alterations in TP53 (72.0%, 528/733), ERBB2 (25.6%. 188/733), RAD21 (14.1%, 103/733), NF1 (9.0%, 66/733), BRCA1 (7.8%, 57/733), and ESR1 (6.3%,46/733) (p <\u20090.05 for all comparisons). Immune checkpoint inhibitor (ICPI) biomarkers such as tumor mutational burden (TMB)-High (16.2%, 119/733), microsatellite instability (MSI)-High (1.9%, 14/733), CD274 amplification (3.6%, 27/733), and APOBEC mutational signature (5.9%, 43/733) were significantly higher in the BCBM cohort compared to the primary BC cohort (p <\u20090.05 for all comparisons). When using both CGP and PD-L1 IHC, 37.5% (6/16) of the TNBC brain metastasis patients were eligible for atezolizumab based on PD-L1 IHC, and 18.8% (3/16) were eligible for pembrolizumab based on TMB-High status.\n\n\nCONCLUSION\nWe found a high prevalence of clinically relevant genomic alterations in BCBM patients, suggesting that tissue acquisition (surgery) and or cerebrospinal fluid (CSF) for CGP in addition to CGP of the primary tumor may be clinically warranted.\n\n\nIMPLICATIONS FOR PRACTICE\nWe found a high prevalence of clinically relevant genomic alterations in BCBM patients, suggesting that tissue acquisition (surgery) and or cerebrospinal fluid (CSF) for CGP in addition to CGP of the primary tumor may be clinically warranted. In addition, we identified higher positive rates for FDA-approved immunotherapy biomarkers detected by CGP in BCBM patients, opening the possibility for new on-label treatments. Last, we noted limited correlation between TMB and PD-L1 IHC which exemplifies the importance to test with both PD-L1 IHC and CGP for ICPI eligibility of TNBC patients with brain metastases.