Real-world Outcome of Neoadjuvant Therapy with or Without Pembrolizumab for Triple-Negative Breast Cancer

Background and purpose: Neoadjuvant therapy (NAT) has become standard therapy for early triple-negative breast cancer (TNBC). The aim of this study was to report real-world outcome of TNBC treated with NAT with or without pembrolizumab and to identify predictive factors for achieving pathologic complete response (pCR) in the pembrolizumab cohort. Patient/material and methods: The data of 75 consecutive TNBC patients treated with neoadjuvant chemotherapy and pembrolizumab at the Helsinki University Hospital Comprehensive Cancer Center were retrospectively collected. Treatment outcome and predictive factors for pCR were analyzed. Additionally, the outcome of nonmatched 102 consecutive TNBC patients treated without pembrolizumab during the preceding years is reported. Results: Forty-two patients (56.0%) achieved pCR to pembrolizumab-based NAT, while 47 patients (46.1%) without pembrolizumab had pCR. Lymph node metastasis (p = 0.011) and multifocality (p < 0.001) were inversely associated with pCR in the pembrolizumab cohort. Thirty-four patients (45.3%) had immune-related adverse events (irAEs), and 11 patients (14.7%) had grade 1–2 myocarditis in the pembrolizumab cohort. Due to adverse events (AEs), pembrolizumab was discontinued in 22 patients (29.3%) in the neoadjuvant setting, not started postoperatively in 21 patients (28%) and discontinued postoperatively in eight patients (10.7%). The number of preoperative pembrolizumab cycles was not associated with pCR. Interpretation: Despite higher incidence of myocarditis and interruption of the systemic therapy due to irAEs, higher pCR rates were seen with pembrolizumab. Even though the number of preoperative pembrolizumab cycles was not associated with pCR monitoring and limiting AEs is important.