These data suggest that there is a more complex mechanism of action for IDO1 than previously appreciated, perhaps because of its association with CD8+ T cell infiltration in a “hot” microenvironment or the correlation between high IDO1 and high STAT1, a molecule important for amplifying cancer immunity46; the correlation between IDO1 and CXCL10 may also be important because the latter acts to promote T cell infiltrates. This evidence concerns the gene IDO1 and cancer.