Background: African Americans (AA) have the highest breast cancer (BC) mortality rate. Access to treatment is a known contributing factor. In the past 4 years, several targeted therapies for HER2- BC have become available which require testing for specific biomarkers. This study assessed the impact of race on biomarker testing rates in HER2- ABC pts receiving treatment in the US. Methods: Oncologists were recruited to abstract data from medical charts for the next 8-10 pts receiving treatment with HER2- ABC during Sept 2019-Apr 2020. Pts records were stratified by race and categorized into 3 mutually exclusive cohorts [White/Caucasian (White), AA, Other]. The other race cohort was excluded from this analysis due to small sample size. Differences in pt demographics/clinical characteristics were analyzed via Fisher’s exact tests. Testing rates for actionable biomarkers (i.e. BRCA1/2, PIK3CA, PD-L1) were compared between White and AA pts utilizing logistic regressions controlling for age, known family history of a BRCA-related cancer, hormone receptor (HR) status and practice setting (academic vs. community). Further analyses by age will be presented. Results: This analysis included 378 pts records, provided by 40 oncologists. Mean age was 64 years; 77% had HR+/HER2- ABC; 20% had advanced triple negative breast cancer (TNBC), 3% had ABC with an unknown HR status. Compared to White pts, AA pts were significantly more likely to have advanced TNBC (27% vs. 18%, p<0.05). Compared to White pts, AA pts had significantly lower BRCA1/2 mutation (mut) testing rates (Table). Numerically lower rates of PIK3CAmut and PD-L1 testing were observed among AA pts (Table). BRCA1/2mut positivity rate (germline [g] and/or somatic [s]) was higher among AA vs. White pts (30% vs. 22%). Positivity rate for PIK3CAmut was lower for AA vs. White pts (8% vs. 11%). Conclusions: A higher than expected BRCA1/2mut positivity rate was observed than previously reported in the literature. This is likely because this analysis included sBRCA1/2mut and represented a high risk pt population. Across all biomarkers assessed, AA pts had lower testing rates than White pts. This suggests racial disparities in testing rates of actionable biomarkers. Consistent with guidelines, and with the increased availability of targeted therapies, focused efforts should be developed to increase biomarker testing in AA pts. Funding: Pfizer Biomarker Testing Rates by Race.

^aReference value (ref) ^bCompared to ref, <1 is lower testing rates, 1 = the same testing rates, >1 is higher testing rates.