IDO1 and cancer: While IDO expression is correlated with a less favorable prognosis for many types of cancer including colorectal [12], uterine cervical [13], endometrial [14], breast [15], melanoma [16], ovarian [17], and lung cancer [18], IDO expression is also associated with recurrence-free survival of hepatocellular patients [19] and the long-term survival of patients with renal carcinoma [20].