IDO1 and esophageal squamous cell carcinoma: Zhou et al. [68] reported that the pathologic complete response (pCR) rates of IDO+PD-L1+, IDO+PD-L1− or IDO−PD-L1+, and IDO−PD-L1− ESCC patients were 21.4%, 34.5%, and 57.3%, respectively (P = 0.001).