TNFRSF9 and head and neck squamous cell carcinoma: The study showed that HPV-positive and HPV-negative tumors possessed a high expression of CD137 on tumor infiltrating NK cells in vivo while peripheral NK cells after cetuximab administration showed higher expressions of CD137 in HPV-positive HNSCC signifying improved outcomes of HPV-positive HNSCC treated with combination cetuximab and urelumab.