Tumor and lymph node lymphangiogenesis--impact on cancer metastasis

The extent of lymph node (LN) metastasis is a major determinant for the staging and the prognosis of most human malignancies and often guides therapeutic decisions. Although the clinical significance of LN involvement is well documented, little has been known about the molecular mechanisms that promote tumor spread via lymphatic vessels to sentinel and distal LN and beyond. However, recent discoveries have identified novel lymphatic-specific markers, and the newly discovered lymphangiogenesis factors vascular endothelial growth factor-C (VEGF-C) and VEGF-D were found to promote tumor-associated lymphatic vessel growth in mouse tumor models, leading to enhanced tumor spread to sentinel LN. Our recent findings indicate that VEGF-A also acts as a potent tumor lymphangiogenesis factor that promotes lymphatic tumor spread. VEGF-A overexpressing primary tumors induced sentinel LN lymphangiogenesis even before metastasizing and maintained their lymphangiogenic activity after metastasis to draining LN. Our recent studies showed that primary human melanomas that later metastasized were characterized by increased lymphangiogenesis and that the degree of tumor lymphangiogenesis can serve as a novel predictor of LN metastasis and overall patient survival, independently of tumor thickness. Tumor lymphangiogenesis also significantly predicted the presence of sentinel LN metastases at the time of surgical excision of the primary melanoma. Together, these findings suggest that tumor lymphangiogenesis actively contributes to cancer dissemination, that blockade of lymphatic vessel growth might inhibit tumor metastasis to LN, and that the extent of tumor-associated lymphangiogenesis could serve as a novel, prognostic parameter for the metastatic risk of human cancers.