Neoadjuvant chemotherapy is routinely assigned to women with early-stage breast cancer, but approximately 25% of them experience a recurrence within 5 years. Combining pembrolizumab, a humanized antibody, with neoadjuvant chemotherapy (NACT) for early-stage breast cancer, is likely to improve the outcomes. This study aims to evaluate the efficacy of pembrolizumab plus NACT in patients with early-stage breast cancer.

This randomized, open-label, multicenter, phase 3 clinical trial included a total of 250 women with early-stage, ERBB2-negative breast cancer. The participants were randomly assigned to receive taxane- and anthracycline-based NACT with (n=69) or without (n=181) pembrolizumab. Patients assigned to pembrolizumab were further divided into four groups: ERBB2-negative, HR-positive/ERBB2-negative, and triple-negative. The primary outcome of the study was pathologic complete response (pCR), along with residual cancer burden (RCB) and 3-year event-free and recurrence-free survival.

The final estimated pCR rates in the ERBB2-negative, HR-positive/ERBB2-negative, and triple-negative groups were 44% vs. 17%, 30% vs. 13%, and 60% vs. 22%, respectively. Pembrolizumab lowered the disease burden (RCB) for each group. Treatment-related adverse events included thyroid abnormalities (13.0%) and adrenal insufficiency (8.7%).

The research concluded that neoadjuvant chemotherapy, in combination with pembrolizumab, was two-fold more effective in increasing pCR rates in all the cohorts.