HGF and neoplasm: The signaling of the HGF/Met pair and of its homologs (the Ron ligand is a macrophage-stimulating protein or MSP and is a homolog of HGF [21,24]) are crucial for some steps of embryonic development and tissue regeneration in physiological conditions, while the same signal transduction, when dysregulated, may run the processes of tumor growth and metastasis [11].