Regarding IDO2, we could assume a similar role, resulting both in the induction of and in the resistance to the host's immune system (13, 23, 26, 34, 37, 38, 60); consequently, IDO2 could be implicated either in delaying or promoting tumor aggressiveness, based on the highly fluctuating interactions with all of the other activated molecules of the tumor microenvironment (11, 13, 25, 26, 34). This evidence concerns the gene IDO2 and neoplasm.