Advances in the research on lymphangiogenesis in carcinoma tissues (Review).

Metastatic spread of tumors is an important prognostic factor for cancer patients. The effect of angiogenesis on cancer cell proliferation and metastatic spread has been confirmed. However, less attention has been focused on research involving tumor lymphangiogenesis as opposed to research on tumor angiogenesis, due to the lack of specific markers for lymphatic vessel endothelial cells (LVECs). Recently, the improvement of isolation techniques for LVECs and the discovery of specific LVEC markers such as vascular endothelial growth factor receptor-3 (VEGFR-3), podoplanin, lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) and Prox1 have led to advances in research involving lymphangiogenesis in carcinoma tissues. New lymphatic vessels in tumor tissues may originate from bone marrow endothelial progenitor cells, directly from the preexisting lymphatic vessels, and even by cell transformation. Peritumoral lymphatic vessels play a more important role in the process of tumor metastasis by providing more channels for lymphatic invasion and metastatic spread. The molecular mechanism of tumor lymphangiogenesis is complicated, and numerous factors such as VEGF-A, platelet-derived growth factors (PDGFs), hepatocyte growth factor (HGF), fibroblast growth factor-2 (FGF-2), and angiopoietins (Ang) are directly or indirectly involved in the process. However, it has been demonstrated that the VEGF-C/VEGF-D/VEGFR-3 signaling pathways are the most important mechanism underlying tumor lymphangiogenesis.