Breast Cancer Study of Preoperative Pembrolizumab + Radiation

This study is being done to assess the feasibility of pembrolizumab (study drug) combined with standard radiation to the tumor (tumor boost) before patients undergo standard treatment that can consist of one or more of the following: breast-conserving surgery, radiation to the entire breast/chest wall after surgery, and chemotherapy. Study participants will receive two doses of the study drug intravenously (through the vein) before their planned breast surgery or chemotherapy. The study drug will be administered three weeks apart. At the time of the second dose, radiation to the tumor in the affected breast will be given. This type of radiation treatment is called a "tumor boost", which is a standard part of radiation therapy for breast cancer that may occur either before or after planned breast-conserving surgery. Patients will receive breast surgery or begin chemotherapy approximately six weeks after your first dose of the study drug.

With more than 1 million new cases diagnosed yearly worldwide, breast cancer is a global public health burden. Over the past decade, molecular subtyping of breast cancer has identified intrinsic subtypes that may be at enhanced risk for both local and distant recurrence. This study focuses on the immunogenicity of high-risk breast cancer subtypes that are likely to display a dense lymphocytic infiltration including including TNBC and HR+/HER2- tumors. Immune build up via immune co-stimulatory molecules permits the ensuing immune response to strengthen and destroy cancer systemically. Thus, the effect of the anti-tumor immune response initiated by the radiation to an intact tumor by combination with checkpoint blockade is increased. Pembrolizumab is an optimal immunotherapy agent to study, as this agent has recently been FDA approved for use in multiple tumor types. It is therefore ready to be tested for efficacy in other disease sites and in combination with other treatments.