However, although IDO1 and its metabolites have been reported to directly promote the cell proliferation and tumorigenesis and inhibit apoptosis in colon cancer cells32–34, our current data could still not establish a direct causal link between the tumor regression and the reduced IDO1 expression following the treatment with BET inhibitors, which requires additional investigations. The gene discussed is IDO1; the disease is malignant colon neoplasm.