Lymphangiogenesis and tumor metastasis.

In several human cancers, increased expression in primary tumors of vascular endothelial growth factor-C (VEGF-C) is correlated with regional lymph node metastasis. Studies using transgenic mice overexpressing VEGF-C, or xenotransplantation of VEGF-C-expressing tumor cells into immunodeficient mice, have demonstrated a role for VEGF-C in tumor lymphangiogenesis and the subsequent formation of lymph node metastasis. However, at variance with data obtained in animal models, there is at present very little evidence for lymphangiogenesis in human tumors. Nonetheless, the striking correlation between levels of VEGF-C in primary human tumors and lymph node metastases exists, which suggests that VEGF-C may serve functions other than lymphangiogenesis. Thus, VEGF-C may activate pre-existing lymphatics which in turn become directly involved in tumor cell chemotaxis, intralymphatic intravasation and distal dissemination. A reciprocal dialogue is therefore likely to exist between tumor and lymphatic endothelial cells which results in the formation of lymph node metastases.