THBS1 and head and neck squamous cell carcinoma: In addition, several other angiogenic factors have been implicated in promoting angiogenesis in HNSCC, including connective tissue growth factor (CTGF), platelet-derived growth factor (PDGF) and angiogenin (ANG), whereas endostatin (END) and thrombospondin-1 (THBS1) have been investigated as endogenous angiogenesis inhibitors.6,7,8,9