Expression of IDO1 in tumor cells is associated with significantly worse clinical prognosis and reduced overall survival in many cancer types including ovarian cancer [7], malignant melanoma [8,9], pediatric [10] and adult acute myelogenous leukemia [11,12], colorectal cancer [13], prostate cancer [14], endometrial cancer [15], as well as in pancreatic cancer [16]. This evidence concerns the gene IDO1 and endometrial cancer.