Background: The phase Ib KEYNOTE-173 study was conducted to assess the safety and preliminary antitumor activity of neoadjuvant chemotherapy plus pembrolizumab in high-risk, early-stage, non-metastatic triple-negative breast cancer (TNBC). Patients and methods: Six pembrolizumab plus chemotherapy regimens were evaluated (cohorts AeF). All cohorts received a pembrolizumab 200-mg run-in dose (cycle 1), then eight cycles of pembrolizumab in combination with a taxane with or without carboplatin for 12 weeks, and then doxorubicin and cyclophosphamide for an additional 12 weeks before surgery. Primary end points were safety and recommended phase II dose (RP2D); secondary end points were pathological complete response (pCR) rate, objective response rate, and event-free and overall survival. Exploratory end points were the relationship between outcome and potential biomarkers, such as tumor programmed death ligand 1 (PD-L1) expression (combined positive score) and stromal tumor-infiltrating lymphocyte levels (sTILs). Results: Sixty patients were enrolled between 18 February 2016, and 28 February 2017. Dose-limiting toxicities occurred in 22 patients, most commonly febrile neutropenia (n ¼ 10 across cohorts). Four cohorts (B, C, D, F) did not meet the RP2D threshold; two cohorts did (A, E). The most common grade !3 treatment-related adverse event was neutropenia (73%). Immune-mediated adverse events and infusion reactions occurred in 18 patients (30%) and were grade !3 in six patients (10%). The pCR rate (ypT0/Tis ypN0) across all cohorts was 60% (range 49%e71%). Twelve-month event-free and overall survival rates ranged from 80% to 100% across cohorts (100% for four cohorts). Higher pre-treatment PD-L1 combined positive score, and pre-and on-treatment sTILs were significantly associated with higher pCR rates (P ¼ 0.0127, 0.0059, and 0.0085, respectively). Conclusion: Combination neoadjuvant chemotherapy and pembrolizumab for high-risk, early-stage TNBC showed manageable toxicity and promising antitumor activity. In an exploratory analysis, the pCR rate showed a positive correlation with tumor PD-L1 expression and sTIL levels. Trial registration: ClinicalTrials.gov identifier: NCT02622074.

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Background: T-DXd is a HER2-targeting antibodyedrug conjugate approved for pts with advanced HER2+ mBC based on the results from DESTINY-Breast01 (NCT03248492). This is the first report of DESTINY-Breast03 (NCT03529110), a multicenter, open-label, randomized phase 3 study comparing the efficacy and safety of T-DXd vs T-DM1 in pts with HER2+ mBC previously treated with trastuzumab and taxane. This is the first reported randomized study of T-DXd in BC.Methods: Pts were randomized 1:1. The primary endpoint was progression-free survival (PFS) by blinded independent central review (BICR). Secondary endpoints include overall survival (OS), objective response rate (ORR), duration of response, PFS by investigator, and safety.