TGFB1 and head and neck squamous cell carcinoma: In HPV− HNSCC the induction of apoptosis might be less efficient, as we also did not find apoptotic cells in MMC-treated SCC-25 culture, and a combination of survival factors as TGF-β1 and EGF, FGF, NGF or BDNF could support the survival of the treated cells.