IDO1 and neoplasm: The expression of IDO in tumor cells was significantly higher in DEB-SCCs (mean H-score: 48.32) compared with KEB-SCCs (mean H-score: 10.8; p = 0.0038), IC-SCCs (mean H-score: 15.34; p < 0.0001), and IS-SCCs (mean H-score: 6.585; p < 0.0001) (Figure 2).