SMAD2 and head and neck squamous cell carcinoma: Alterations in TGF-β signaling, such as a decrease in the expression of transforming growth factor-b type II receptor (TGFβRII), SMAD4, and SMAD2, or an increase in the expression of TGF-β1 ligand plays a prominent role in HNSCC pathogenesis4,25,26,28.