Immunotherapy is revolutionizing the management of multiple solid tumors, and early data have revealed the clinical activity of programmed cell death-1/programmed death ligand-1 (PD-1/PD-L1) antagonists in small numbers ofClinical activity appears more likely if the tumor is triple negative, PD-L1+, and/or harbors higher levels of tumor-infiltrating leukocytes. patients with metastatic breast cancer.