A clinical trial using the IDO1 inhibitor Epacadosta and gene disruption blocking IDO1 activity in colorectal cancer cells has demonstrated that IDO1 inhibition enhances the effects of radiation therapy for colorectal cancer, and provides basic principles and mechanism insights for the study of IDO1 inhibitors as adjunct therapy to radiotherapy in patients with locally advanced sporadic and colitis associated colorectal cancer (Fig. 3) [154]. This evidence concerns the gene IDO1 and colorectal cancer.