CD274 and neoplasm: Furthermore, PD-L1 seems to play not only a role in the interaction with PD-1 on lymphocytes, but also by itself on tumor cells by inducing cell proliferation, as it has been reported in literature that PD-L1 expression increases the levels of Ki-67 and other proteins involved in tumor cell proliferation, thus suggesting that it could become a marker of tumor aggressiveness11.