Background: The NeoImmunoboost study (NCT03289819) was designed to evaluate the pathological complete response (pCR) rate and safety of a neoadjuvant combination of the PD-1 antibody pembrolizumab and nab-paclitaxel followed by pembrolizumab with epirubicin and cyclophosphamide in patients with early triple negative breast cancer (TNBC). Methods: This is a prospective, single-arm, multi-center, open-label phase II clinical trial. Female patients with early TNBC were eligible for trial participation. Patients received 12 cycles of weekly nab-paclitaxel intravenous (i.v.) 125 mg/m² body surface area (BSA) in combination with 4 cycles of pembrolizumab i.v. 200 mg q3w; followed by 4 cycles of epirubicin i.v. 90 mg/m² BSA and cyclophosphamide i.v. 600 mg/m² BSA q3w in combination with 4 cycles of pembrolizumab i.v. 200 mg q3w. After 25 patients the protocol was amended, with an initiation boost of 1 cycle of pembrolizumab i.v. 200 mg q3w monotherapy prior to the chemotherapy. Primary trial endpoint was pCR. Secondary endpoints included safety and clinical response rate. Results: Between March 2018 and October 2019, 53 patients were included into the trial. Until now, 47 patients have completed trial treatment and 6 patients are still receiving therapy. 28 patients have received the initiation boost with pembrolizumab, 25 patients did not receive the initiation boost. Up to now, 4 patients terminated the therapy prematurely. Conclusions: pCR data of all patients will be available at the meeting and results of the pCR rates and selected secondary endpoints will be presented at the meeting. Clinical trial information: NCT03289819