HGF and neoplasm: Within the tumor microenvironment, several of the growth factors secreted by stromal or tumor cells, including HGF, insulin-like growth factor 1 (IGF1), epidermal growth factor (EGF), vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF), may induce a similar signaling cascade downstream of receptor tyrosine kinase (RTK) and trigger synergistic tumor recurrence and metastasis (11).