IDO1 and neoplasm: To verify that the RIME‐MLL1‐H3K4me3 axis is clinically associated with ESCC development, we performed immunohistochemistry analysis and evaluated CD68, MLL1, PD‐L1, IDO‐1, CD8 and GranB expression in tumour tissues from a cohort of ESCC patients (SYSUCC, n = 70).