RecruitingPhase 1Drug trialEffects of MK-3475 (Pembrolizumab) on the Breast Tumor Microenvironment in Triple Negative Breast CancerAssess response to pembrolizumab in both primary tumor, normal breast stroma, circulating lymphocytes and serum exosomes in treatment naive triple negative breast cancer (TNBC) patients. Assess for change in tumor-infiltrating lymphocytes (TILS) both stromal (sTILS) and intraepithelial (iTILS) in newly diagnosed early stage TNBC patients treated with two doses of MK-3475 prior to lumpectomy.