IDO1 and esophageal squamous cell carcinoma: In summary, serum HMGB1 and IDO are abnormally high expressed in ESCC patients, and HMGB1 may promote the expression of IDO through NF-κB signaling pathway, which may regulate the functional phenotype of T lymphocytes, inhibit the immune function of the body, promote tumor progression in ESCC patients and cause poor prognosis.