ERBB4 and head and neck squamous cell carcinoma: Various RTKs and non-RTK family of angiogenic and growth regulatory factors including VEGFR1, ERbB4, FGFR3/4, c-RET, CXCL16, TSP-1, IGFBP3 and IL-8 are involved and implicated in the overwhelming network of HNSCC angiogenesis, proliferation, invasion/metastasis and therapeutic resistance [20-30].