CD274 and neoplasm: T cell co-inhibitory molecules belonging to the B7 family in the tumor microenvironment, such as PD-L1 provide critical inhibitory signals and have been recognized as a major immune inhibitory mechanism in diverse solid tumors.1–4 Antibodies that inhibit the PD-1/PD-L1 pathway produce durable clinical responses in various solid malignancies, including breast carcinomas, yet it appears to benefit only a subset of breast tumors.5–11