DISP-19. ETHNIC DISPARITIES IN METASTASIS PATTERNS AND TREATMENT UTILIZATION AMONG METASTATIC BREAST CANCER PATIENTS WITH BRAIN METASTASIS: A RETROSPECTIVE ANALYSIS OF US HEALTH SYSTEMS DATA (2019-2023)

Abstract INTRODUCTION The treatment landscape for metastatic breast cancer (MBC) with brain metastasis (BM) has evolved due to novel therapies. However, outcomes remain poor and vary among groups. This study investigated ethnic disparities in metastasis (mets) patterns and treatment use among MBCBM patients (pts). METHODS We analyzed deidentified data from seven US health systems in the Guardian Research Network from December 2019 to December 2023. Pts with MBC were categorized by IHC scores: hormone receptor+/HER2-, HER2-low (IHC 1+ or 2+ with negative FISH), HER2 positive, and Triple Negative (TNBC). We used descriptive and comparative statistical analysis. RESULTS Of 421 MBC pts, 200 (47.5%) had HER2+, 167 (39.7%) had HR+/HER2-, and 54 (12.8%) had TNBC. 159 (37.7%) were reclassified as HER2-low, primarily from HR+/HER2- (127; 76.0%) and TNBC (32; 59.3%). Bone mets developed in 29.6% of pts, more prevalent in HER2+ (39.5%), TNBC (25.9%), and HR+/HER2- (19.1%) groups. Non-Hispanics showed higher BM prevalence (74.4% vs. 25.6%). HR+/HER2- BM pts had higher bone mets (71.88%) than HER2+ BM (65.82%). TNBC BM pts had the highest rate of liver mets (57.1%). HER2-low BM pts showed mets across liver (40%), lung (34.29%), and bone (68.57%). In the HER2+ BM group, non-Hispanics had higher liver (40.13% vs. 32.35%) and bone mets (69.08% vs. 52.94%) than Hispanics. In TNBC BM group, Hispanics had higher liver mets (66.67% vs. 35%), while non-Hispanics had higher lung mets (32.5% vs. 11.11%). Both ethnic groups in HR+/HER2- category had high bone mets (78.95% vs. 73.33%). There were disparities in the use of CDK4/6 inhibitors, ICIs, and mTOR inhibitors, with Hispanics frequently using them. CONCLUSION HR+/HER2- BM pts were most affected by bone mets, followed by HER2+ BM. TNBC BM pts predominantly had liver mets. Non-Hispanics had higher BM prevalence. Hispanics frequently used ICIs, CDK4/6 and mTOR inhibitors, which were more frequently used by Hispanics. Further research should explore these disparities in mets patterns, treatment choices, and responses.