IDO1 and neoplasm: There is evidence of an association of increased IDO1 expression with clinical characteristics of solid tumors, such as tumor differentiation (OR = 1.81, 95% CI = 1.05–3.12, p = 0.033), the presence of distant metastasis (OR = 1.45, 95% CI = 1.02–2.06, 0.039), and TNM stage (OR = 1.89, 95% CI = 1.13–3.17, p = 0.015) [105].