CD274 and cancer: PD-L1 expression may be expressed constitutively on cancer cells or may be induced by cytokines such as gamma interferon secreted by activated T cells.31 Indeed, classification of tumors into four groups based on the presence or absence of TILs and PD-L1 expression on cancer cells has been proposed to guide immune therapy approaches.32 It is likely that further characterization of the subset of TILs will also be important in planning tumor specific immune approaches.