Co-citation and keyword analysis revealed key research themes, including “IDO (indoleamine 2,3-dioxygenase),” “tryptophan catabolism,” “cancer,” and “dendritic cells,” as well as emerging topics such as “gut microbiota,” “tumor microenvironment,” “aryl hydrocarbon receptor,” and “cancer immunotherapy.” The gene discussed is IDO2; the disease is neoplasm.