Further, a retrospective study identified five most significantly overexpressed immune-related genes in HNSCC: TNFRSF9/4-1BB (77%), IDO1 (75%), TNFSF4/OX40L (74%) and TNFRSF18/GITR (74%), and FOXP3 (62%). The gene discussed is IDO1; the disease is head and neck squamous cell carcinoma.