IDO1 and neoplasm: In castration-resistant prostate cancer (CRPC), MUC1-C protein activation promotes an immunosuppressive environment through the Type II IFN-γ pathway and affects chromatin remodeling, with MUC1-C regulating IDO1, WARS, and PTGES expression, thereby metabolically suppressing the tumor microenvironment and aiding tumor survival and progression, as observed by Hagiwara et al.