155P From bench to equity: Closing the knowledge gap on racial differences in TNBC response to immunotherapy

Neoadjuvant chemoimmunotherapy has emerged as the standard of care treatment for patients with stage II/III triple-negative breast cancer (TNBC) based on the results of the KEYNOTE-522 trial (KN522) demonstrating higher pathological complete response (pCR) rates and superior event-free survival (EFS) compared to standard therapy. Few African American patients were enrolled in the KN522 study, and our understanding of the real-world efficacy and tolerability of the KN522 regimen among patients who are disproportionately affected by TNBC is limited. A multicenter retrospective analysis conducted of patients with stage II/III TNBC treated with KN522. Primary objective was to compare pathological complete response (pCR) rates between race groups. Secondary objectives were treatment discontinuation rates and immune-related adverse events (irAEs) by race. Chi-square and Fisher exact tests were performed using SAS version 9.5 to investigate differences among racial groups. 63 patients were eligible. 73% of patients were AA, 22% White, 1.6% Hispanic, and 3.2% Native American. 54% had lymph node involvement. Grade 3 tumors were observed in 87% of patients. pCR rate among all patients who completed the full regimen was 45.9%, with a numerically higher, but not statistically significant rate in AA patients (53.2%) compared to White patients (28.6%) (p-value 0.230). Treatment discontinuation occurred in 41% of the cohort, primarily due to cytopenia. Discontinuation rates were higher in AA patients (45.7%) compared to White patients (35.7%) (p value 0.632). irAEs were reported in 16% of patients. IrAEs were noted less in AA (13%) compared to non-AA (23%) groups. Most common irAEs were hypothyroidism and hepatitis. This real-world study suggests promising KN522 efficacy in early-stage high-risk TNBC for AA women, with pCR rates comparable to the KEYNOTE-522 trial. Higher discontinuation rates in AA patients highlight the need for further investigation into potential contributors. Understanding the imppact that social determinants of health play in AA patients' ability to complete their treatment will be critically important to optimize KN522 delivery and to improve outcomes.