TNFRSF9 and head and neck squamous cell carcinoma: Based on our earlier findings, secretory 4-1BB levels are higher in the plasma of patients with OC and OPC than in healthy controls (HC).6To employ 4-1BB as an immunotherapy, we evaluated the levels of4-1BBexpression in lymphocytes from HNSCC patients, including peripheral blood mononuclear cells (PBMCs) and tumor infiltrating lymphocytes (TILs).