IDO1 and esophageal squamous cell carcinoma: ROC curves results showed that serum HMGB1, IDO, CEA and SCC-Ag all had predictive ability for clinical progression of ESCC, among which the predictive value of combined detection of serum HMGB1 and IDO (AUC=0.888, P<0.001) was significantly higher than that of CEA and SCC-Ag (AUC=0.754, P=0.001).