IDO1 and inflammatory bowel disease: Interestingly, high expression of IDO1 has also been observed in experimental murine colitis and in human inflammatory bowel disease, a condition that is associated with a significant increase in the risk of CRC (Wolf et al, 2004; Ferdinande et al, 2008; Hansen et al, 2009), further suggesting a role for IDO1 in the development and progression of CRC.