The mechanisms of IDO expression increase in tumor tissues mainly include the absence of tumor suppressor gene Bin1 (Bridging integron‐1),199 the expression of tumor microenvironment interferon,200 and COX‐2 promoting IDO expression,201 etc The overexpression of IDO is largely related to the poor prognosis of tumor.202. The gene discussed is IDO1; the disease is neoplasm.