IDO1 and neoplasm: Thus, enthusiasm for IDO1 inhibitors was not extinguished, and with revised clinical strategies, development of several inhibitors was restarted across a range of tumor types, including metastatic prostate (24), bladder (25, 26), glioblastoma (27), endometrial (28), hepatocellular (29), and head and neck squamous cell carcinoma (30), with most studies including combinations with immunotherapy.