Abstract PS4-10-30: Evaluating real world pathologic complete response (pCR) rates at an urban center following the KEYNOTE-522 regimen for early-stage TNBC

Abstract Background: Neoadjuvant chemoimmunotherapy has been the standard frontline treatment for early-stage TNBC since 2021, when the KEYNOTE-522 trial demonstrated a significantly higher pCR rate of 64.8% with chemotherapy and pembrolizumab compared to chemotherapy alone. Our study aims to determine the efficacy of the KEYNOTE-522 regimen, as measured by pCR, in a real-world, diverse, urban population at a large tertiary referral center and assess factors impacting the likelihood of pCR. Methods: We performed a retrospective chart review of patients (pts) with anatomic Stage II-III TNBC who received the KEYNOTE-522 regimen within our institution’s health system from August 2021 to February 2025. Pts who completed neoadjuvant chemotherapy and pembrolizumab and underwent surgery were included. Demographics, clinicopathologic characteristics, treatment sequence and schedule, surgery type, and pCR rates were extracted from the medical record. Descriptive statistics were used to describe patient data. Non-parametric tests were used to evaluate differences between clinical factors across continuous and categorical variables: Wilcoxon rank sum and Kruskal-Wallis rank sum for continuous variables, and chi square tests (or Fisher’s exact tests) for categorical variables. Due to the exploratory nature of our analysis, p-values are reported unadjusted. Results: We identified 104 pts who were treated with neoadjuvant KEYNOTE-522 and underwent surgery. Overall, 83% of patients were stage II and 43% had lymph node involvement. 34% of pts (N=35) identified as White, 25% (N=26) Black, 16% (N=17) Hispanic, 15% (N=16) Asian, and 9.6% (N=10) as Other. The median age of the cohort was 55. The pCR rate of our cohort was 60% (N=62). When stratified by race/ethnicity, Asian and Hispanic patients had higher pCR rates than White and Black patients, p=0.01 (Table 1). There was no statistically significant difference in pCR based on age. 32% (N=33) of pts 50 years and 68% (N=71) of pts 50+ years achieved pCR (p=0.063). 64% of pts (N=67) received chemotherapy with paclitaxel and carboplatin (TC) first, while 36% received doxorubicin and cyclophosphamide (AC) first. There was no significant difference in pCR rate (p=0.694) based on which regimen was given first; however, there was a statistically significant difference in pts who received dose-dense AC every 2 weeks (69%, N=44) vs. every 3 weeks (45%, N=18, (p=0.016). Although 47% (N=49) of patients did not complete 8 neoadjuvant cycles of pembrolizumab, this did not impact likelihood of pCR (p=0.315). Conclusion: In a diverse real-world population, pCR rates were similar to those in the KEYNOTE-522 trial. The higher pCR rates in Asian and Hispanic patients warrants further study. Dose dense AC administered every 2 weeks was associated with a higher pCR rate. Limitations of this analysis include its retrospective design and small sample size. Citation Format: J. Anderson, J. Dejesus, E. Baldwin, G. Van Hyfte, P. Pandu, N. Krishnamurthy, R. Farley, M. Rattu, R. Patel, A. Tiersten. Evaluating real world pathologic complete response (pCR) rates at an urban center following the KEYNOTE-522 regimen for early-stage TNBC 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 PS4-10-30.