CD274 and plasma cell myeloma: More and more research and clinical studies have focused on linking immunological checkpoints in this PD-1/PD-L1 pathway with the prognosis and progression of many neoplastic diseases, including kidney cancer [35], chronic lymphocytic leukemia [36,37], multiple myeloma [38], melanoma [39], breast cancer [40], and lung cancer [41], as well as head and neck cancers [42].