ABSTRACT
For many types of human cancer, the expression of vascular endothelial growth factor-C (VEGF-C) correlates with enhanced tumor-associated lymphatic vessel density, metastasis formation and poor prognosis. In experimental animals, VEGF-C produced by primary tumors can induce lymphangiogenesis within and/or at the periphery of the tumor, and promotes metastasis formation. Tumor-induced lymphangiogenesis is therefore thought to expedite entry of tumor cells into the lymphatic vasculature and their trafficking to regional lymph nodes, thereby fostering metastatic dissemination. Tumour-produced VEGF-C can also drain to the regional lymph nodes and induce lymphangiogenesis there. Whether this activity promotes metastasis formation remains unclear. To address this issue we manipulated VEGF-C activity and VEGFR-3 activation in the lymph nodes draining syngeneic rat breast cancers using intra-dermal delivery of either recombinant VEGF-C or VEGFR-3 blocking antibodies to induce or suppress lymph node lymphangiogenesis, respectively. Recombinant VEGF-C induced lymph node lymphangiogenesis, but was not sufficient to promote metastasis formation by poorly metastatic NM-081 breast tumours. Conversely, inhibition of lymph node lymphangiogeneis induced by highly metastatic MT-450 breast tumours suppressed the outgrowth of lymph node metastases, but not the initial colonization of the lymph nodes. Lung metastasis was also not affected. We conclude that tumor-derived VEGF-C draining to regional lymph nodes promotes the outgrowth of lymph node metastases. VEGF-C may induce lung metastasis independently of its effects on lymph node metastasis.
