Notably, IDO1 expression exhibits considerable variability across different tumors, with some immunohistochemical studies suggesting IDO1 positivity rates of 94% in uroepithelial carcinoma, 57-66% in ovarian cancer, 37-46% in breast cancer, 44-81% in renal cancer and 8% in GBM (34). Here, IDO1 is linked to glioblastoma.