In this study, we found that compared to the tumors with low mutation burden (iCAM−), the tumors with high mutation burden (iCAM+) had significantly higher IDO-1 expression in most (6/8) cancer types (Figure 3A), but significantly higher IDO-2 expression in only a minority (3/8) of cancer types (Figure 3B), and significantly higher TDO-2 expression in very few (2/8) cancer types (Figure 3C). Here, TDO2 is linked to cancer.