Abstract PD1-06: Racial/ethnic inequities in access to novel therapies and outcomes in triple negative breast cancer

Abstract Background: Triple negative breast cancer (TNBC) is the most aggressive breast cancer subtype, with Black women facing the highest incidence and poorest survival. While novel therapies, including immunotherapy (IO), antibody-drug conjugates (ADCs), and poly ADP-ribose polymerase (PARP) inhibitors, have improved outcomes, there is limited evidence on whether there are inequities in access and treatment related outcomes. This study examined racial/ethnic inequities in biomarker testing, access to IOs, PARP inhibitors, and ADCs and overall survival (OS), among patients with metastatic TNBC (mTNBC). Methods: We used the US-based Flatiron Health Research Database focusing on women aged ≥18 years, diagnosed with mTNBC between January 2018 and December 2024 (follow up through March 2025). Outcomes included biomarker testing (PD-L1 or BRCA1/BRCA2), use of IO, PARP or ADC, and OS among patients on IO, PARP, or ADC. We estimated a series of multivariable Cox proportional hazard models assessing racial/ethnic inequities in outcomes and potential mediation by area-level social determinants of health (SDOH). Models sequentially adjusted for clinical factors (e.g., age, year of diagnosis, stage) followed by area-level SDOH (neighborhood residential segregation, urbanicity [rural/urban], residence in medically underserved areas, vehicle ownership, and English proficiency). Results: The cohort included 5872 patients (52.5% White, 17.9% Black, 7.0% Latinx, and 20.6% Other/Unknown). Overall, testing rates were about 39% for PD-L1 and 25% for BRCA1/BRCA2. There were no significant racial/ethnic differences in PD-L1 or BRCA1/BRCA2 testing and biomarker positivity rates were similar across groups. However, Black patients were less likely than White patients to receive PARP inhibitors (adjusted HR: 0.64; 95% CI: 0.43-0.96), an inequity partially mediated by SDOH factors (mediated HR: 0.72; 95% CI: 0.30-1.73). Beyond PARP inhibitors, there were no other racial/ethnic differences in treatment receipt. In survival analyses, Latinx patients had better survival than White patients (HR: 0.73; 95% CI: 0.57-0.95), whereas Black patients had worse survival (HR: 1.17; 95% CI: 1.00-1.37). Conclusions: Despite equitable rates of biomarker testing, racial/ethnic inequities exist in access to PARP inhibitors and survival among patients with TNBC. Black patients were less likely to receive PARP inhibitors and had worse OS, with SDOH partially mediating some of these inequities. These findings underscore the need for targeted efforts to address structural barriers to care and promote equitable access to emerging therapies and outcomes in TNBC care. Citation Format: O. M. MbahG. G. HoC. KeaneA. DolorC. Ryals. Racial/ethnic inequities in access to novel therapies and outcomes in triple negative breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PD1-06.