IDO1 expression by tumor cells has been associated with significantly worse clinical prognosis and reduced survival in malignant melanoma [6, 7], pancreatic cancer [8], ovarian cancer [9], both pediatric [10] and adult acute myelogenous leukemia [11, 12], colorectal cancer [13], prostate cancer [14], endometrial cancer [15], and others [16, 17]. This evidence concerns the gene IDO1 and melanoma.