Programmed death ligand 1/PD-L1 (also called B7-H1 and CD274) is a T cell inhibitory molecule that is expressed on antigen presenting cells (APC) leading to T cell anergy and/or apoptosis upon ligation to its receptor Programmed death-1 (PD-1, CD279) on T cells. PD-L1 is expressed on tumor cells of a subset of breast cancer patients. It could also induce EMT and enhance RCC cell cancer stemness through up-regulation of SREBP-1c. Blocking the immunosuppressive PD-1/PD-L1 pathway has antitumor activity in multiple cancer types, and PD-L1 expression on tumor cells and infiltrating myeloid cells correlates with the likelihood of response.