CCL21 and neoplasm: Other ligands and receptors that can also directly or indirectly contribute to lymphangiogenesis under a variety of conditions including wound repair, tissue regeneration and tumor development are VEGF-A/VEGF-R2, Fibroblast Growth Factor (FGF)2/FGF-R, Platelet-Derived Growth Factor (PDGF)/PDGF-R, Hepatocyte Growth Factor (HGF)/C-Met, angiopoietin (Ang)1,2/Tie 2, and chemokine and chemokine receptors CCL21/CCR7 and CXCL12/CXCR4 [21,22,23,24,25,26,27,28,29,30].