Abstract PS2-04-13: Treatment Outcomes Among African American and Non-Hispanic White Breast Cancer Patients Treated with KEYNOTE-522

Abstract Background: Pembrolizumab is used with neoadjuvant chemotherapy in high-risk early-stage triple-negative breast cancer (TNBC).1 Results from the 2021, KEYNOTE-522 trial (KN-522) show improved pathological complete response (pCR) and event-free survival (EFS).1,2 Although TNBC accounts for ∼15% of breast cancers, African American (AA) women experience higher incidence and worse outcomes than Non-Hispanic White women (NHW).3,4 Despite this, AA representation in immunotherapy clinical trials for breast cancer (e.g., KEYNOTE-522, IMPASSION-130, KEYNOTE-355) was <6%1,5,6, highlighting the need for real-world evaluations of treatment outcomes across racial groups. This retrospective study examines real-world toxicities and treatment outcomes of pembrolizumab combined with neoadjuvant chemotherapy in early-stage (I-III) TNBC, based on the KN-522 regimen, with a focus on racial differences between AA and NHW patients. Methods: We abstracted data from early-stage TNBC patients treated with the KN-522 regimen between 2021 and 2024 from an academic comprehensive cancer center. Descriptive analyses were conducted to compare clinical and safety outcomes among AA and NHW patients using ANOVA, Chi-square, or Fisher’s exact tests.7 Univariate and multivariable models evaluated associations between race and toxicity/treatment outcomes. Results: A total of 124 patients were identified: 80 Black (64.5%) and 44 NHW (35.5%), with a median age of 56.5 years (IQR: 42.5-66). Most had T2 tumors (54%), high-grade histology (84.6%), and at least one comorbidity (66.1%). Fifty percent achieved a pCR, while 5.6% experienced disease progression on KN-522, and 8.9% had local/distant recurrence. Significant racial differences were observed in age at treatment initiation (median: 59 years for AA vs. 51.5 years for NHW; p=0.018), BMI (mean: 32.2 vs. 29.1; p=0.026), and marital status (p<0.003). A higher proportion of NHW patients experienced anxiety (31.8% vs. 7.5%; p<0.001) and thyroid disorders (22.7% vs. 7.5%), while hypertension was more common in AA patients (57.5% vs. 29.5%; p=0.003). AA patients had a greater proportion of high-grade tumors (63.4% vs. 36.5%; p=0.576) and HER2-low expression (67.2% vs. 32.7%; p=0.233). pCR was achieved more among AA compared to NHW patients (65% vs. 35%). Although there were no statistically significant differences in overall outcomes across treatment or immune-related adverse events (irAEs), AA patients more frequently experienced treatment-related toxicities, including anemia (63.4% vs. 36.3%), grade 3/4 neutropenia (41.2% vs. 31.8%), and chemotherapy-induced peripheral neuropathy (60% vs. 43.1%). Additionally, treatment modifications related to the KN-522 regimen (p=0.965) and pembrolizumab (p=0.528) were more common among AA patients at 64.3% and 70.9% compared to 35.6% and 29.0% among NHW patients, respectively. Progression-free survival did not significantly differ between AA and NHW patients (p = 0.7562). Both groups exhibited high PFS rates at 12, 24, and 36 months. At 36 months post-treatment, overall survival probabilities for AA patients were 89.7% (95% CI: 76.6%-95.6%) and 97.3% (95% CI: 82.3%-99.6%) among NHW patients Conclusion: This real-world analysis revealed that AA patients receiving KN-522 experienced higher rates of treatment-related toxicities, irAEs, and regimen modifications compared to NHW patients. Despite this, treatment effectiveness was comparable. These findings underscore the need for larger studies to validate outcomes and investigate factors influencing racial differences in treatment response. Citation Format: L. Brock, K. Freeman, A. A. Ashley McCook-Veal, A. Labatut, L. Lei, S. Selimovic, J. M. Switchenko, N. A. Giordano, M. Bhave. Treatment Outcomes Among African American and Non-Hispanic White Breast Cancer Patients Treated with KEYNOTE-522 [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 PS2-04-13.