IDO1 and esophageal squamous cell carcinoma: According to the cut-off values of serum HMGB1 and IDO (2.61ng/mL and 9.66ng/mL) obtained by ROC curve analysis, ESCC patients with different expression levels of HMGB1 were divided into low group (<2.61ng/mL) and high group (≥2.61ng/mL).