Previous studies revealed that IDO1 was highly expressed in multiple tumor types, including lung cancer, breast cancer, colorectal cancer, and renal cell carcinoma [35–39], and many clinical trials are being carried out to test the strategy of the combination of IDO1 inhibitors with conventional treatments, including PD-1 antibodies, chemotherapy, and radiotherapy. This evidence concerns the gene IDO1 and renal cell carcinoma.