Preoperative Immunotherapy Combined With Stereotactic Radiation Therapy Boost in the Treatment of HER2-negative Breast Cancer

The study aims to assess the safety and effectiveness of the combination of anti-PD1 (PD-1, programmed cell death-1) immunotherapy (pembrolizumab) with radiotherapy in the preoperative treatment of triple-negative or luminal HER2-negative (HER2, Human epidermal growth factor receptor 2) (breast cancer, stage IIA/IIB/III/IV (with an acceptable oligometastatic form), resistant to classical chemotherapy After screening and administration of standard induction chemotherapy, the study will be conducted in a group of patients selected on the basis of lack of metabolic response after the 1st cycle of chemotherapy, and the subject of the intervention will be: * addition of preoperative immunotherapy with pembrolizumab or placebo to standard chemotherapy, using a double-blind randomized trial in a ratio of 2:1, respectively * addition of a boost of preoperative robotic stereotactic radiotherapy in all patients, simultaneously with the use of paclitaxel +/- carboplatin and pembrolizumab/placebo.