Among these 15 tumor types, cervical carcinoma (17/17, 100 %), endometrial carcinoma (45/48, 94 %) and bladder urothelial carcinoma (15/16, 94 %) most frequently expressed IDO1, followed by RCC (43/53, 81 %), NSCLC (41/51, 80 %), CRC (46/59, 78 %), head and neck cancer (14/24, 58 %) and melanoma (32/60, 53 %) while most glioblastoma (5/60, 8 %) were negative. Here, IDO1 is linked to head and neck cancer.