IDO1 and neoplasm: The central role of IDO1 in tumor immune evasion has spurred development of multiple pharmacological inhibitors, including epacadostat (INCB024360) and indoximod (1-methyl-D-tryptophan), which have shown promising preclinical efficacy in combination with PD-1/PD-L1 blockade (Zeitler and Murray, 2023).