CD274 and cancer: PD-L1 is expressed on many tumors including cancers developing in various organs such as head and neck, lung, stomach, colon, pancreas, breast, kidney, bladder, ovary, cervix, as well as melanoma, glioblastoma, multiple myeloma, lymphoma, and various leukemias [24-28], thereby inhibits effective anti-tumor immune responses mediated by PD-1-expressed T cells [11].