Real-world clinical outcomes of neoadjuvant pembrolizumab among patients with early-stage triple-negative breast cancer (esTNBC) in a US community oncology setting.

Abstract

e12630 Background: In the KEYNOTE-522 trial, neoadjuvant pembrolizumab plus chemotherapy (P+C) improved pathological complete response (pCR) and long-term survival compared with chemotherapy alone among patients (pts) with early-stage triple-negative breast cancer (esTNBC), with 64.8% achieving pCR and 5-year event-free survival of 81.3% and overall survival of 86.6%. However, clinical outcomes following pembrolizumab initiation in routine clinical practice remain incompletely characterized. This study aimed to describe long-term real-world clinical outcomes among pts initiating pembrolizumab following its U.S. Food and Drug Administration approval in July 2021. Methods: Electronic medical record data from The US Oncology Network identified adult patients with Stage II-III TNBC with documented surgery between 07/01/2021-08/31/2022, who were followed through 07/31/2025. Pts who received pembrolizumab in the neoadjuvant setting were selected. Pt characteristics and provider-documented pCR were described, and survival analysis results were stratified by pCR status. Real-world event-free survival (rwEFS) was assessed from neoadjuvant treatment initiation date to recurrence, progression, or death. Results: There were 182 pts eligible for the study. The majority (99%) of pts received P+C for first neoadjuvant regimen and pembrolizumab monotherapy in the first adjuvant regimen (85%). Overall, 56% (n=102) of pts achieved pCR. Pts with and without pCR were of similar age (median 53 yrs) and duration of follow-up (38 mths), but a higher proportion of pts with pCR had an ECOG of 0 (pCR:46%; no pCR:35%). Overall, median 3-year rwEFS was 87% in the overall population. 3-year rwEFS was significantly better among pts who achieved pCR compared to non-pCR pts (98% vs. 73%, p<0.001). Conclusions: In this real-world cohort of patients with esTNBC treated with neoadjuvant pembrolizumab, favorable 3-year event-free survival outcomes were observed, with significantly improved rwEFS among patients who achieved pathological complete response. These findings highlight the importance of timely access to neoadjuvant pembrolizumab following esTNBC diagnosis. Overall (N=182) pCR (N=102) no pCR (N=80) Age, median (yrs) 53 53.5 53 Follow-up, median (mths) 38.5 38.8 37.9 ECOG 0 at baseline, N (%) 75 (41.2) 47 (46.1) 28 (35.0) Stage III at diagnosis, N (%) 67 (36.8) 36 (35.3) 31 (38.8) 3-year rwEFS, % (95%CI) 87.1 (81.3,91.3) 98.0 (92.4,99.5) 73.1 (61.7,81.6)