IDO1 and head and neck squamous cell carcinoma: APOE, ASNS, CA9, CLSPN, COL6A3, FOXM1, GMPS, HPRT1, IDO1, KPNA2, MYBL2, ODC1, SLC2A1, SLC3A2, SLC7A5, SCLC16A1, STAT1, TFRC, TK1, TIMELESS, and UBE2C were significantly upregulated in HNSCC tissues compared with normal tissues (Figures 6A–U).