We compared the mRNA levels of IDO1 among high-grade (GBM) and low-grade (LGG) glioma downloaded from The Cancer Genome Atlas (TCGA) database, and health tissues (normal) downloaded from the Genotype-Tissue Expression (GTEx) database to illustrate the biological role of IDO1 in GBM progression. Here, IDO1 is linked to glioblastoma.