Impact of Neoadjuvant Pembrolizumab Adherence on Pathologic Complete Response in Triple-negative Breast Cancer: a Real-world Analysis

Background: The addition of pembrolizumab (pembro) to neoadjuvant chemotherapy (NAC) is standard of care for the treatment of early triple-negative breast cancer (TNBC) after KEYNOTE-522 trial demonstrated improved pathologic complete response (pCR) rates with the combination. However, the optimal treatment strategy for TNBC remains uncertain as questions persist about which patients benefit from pembro and the best treatment schedule and regimen. We identified real-world clinical characteristics and treatment variables associated with response to NAC plus pembro.

Methods: Patients with early TNBC treated with NAC plus pembro between February 2020 and September 2023 were identified. Univariate and multivariate analysis was performed using logistic regression to identify factors associated with pCR. Cox proportional hazard prediction models were used to identify predictors of invasive disease-free survival and overall survival in this cohort.

Results: A pCR was achieved in 75 (63.6%) of 118 patients. Age at diagnosis (P = .04), Ki-67 (P = .004), duration from start of pembro to surgery (P = .006) and NAC to surgery (P = .01), number of cycles of pembro (P = .04) and NAC (P = .02), and completion of at least 8 cycles of pembro (P = .015) and NAC (P = .015) were each significantly associated with pCR in univariate analysis. In multivariate analysis, patients younger than 55 years at time of diagnosis (vs age > 55 years) and those completing at least 8 cycles of pembro remained predictive of pCR (OR's 2.50, 2.49, P = .035 and .037, respectively).

Conclusions: In this real-world analysis of patients with TNBC treated with NAC plus pembro, younger age and the completion of at least 8 cycles of pembrolizumab were associated with pCR.