TDO2 and neoplasm: M4112, another IDO1/TDO2 inhibitor, did not present any serious safety concerns at doses up to 800 mg twice daily, though the best overall response observed was stable disease in nine patients (60%) with a progression-free survival of 3.7 months; it is noteworthy, however, that most of these patients had tumor types that are typically unresponsive to immunotherapy (43, 45).