TNF and head and neck squamous cell carcinoma: Furthermore, Gene Set Enrichment Analysis (GSEA) revealed that several representative oncogenic signaling pathways, including tumor necrosis factor (TNF) signaling via NF-kappaB and epithelial mesenchymal transition signaling, were enriched in SCC9 spheres (Figures 1(e) and 1(f)), indicating that CSCs drive tumorigenesis, invasion, and chemotherapy tolerance in HNSCC.