Why and how do tumors stimulate lymphangiogenesis?

Accumulating evidence shows that a subset of solid tumors stimulates lymphangiogenesis, which mediates lymphatic metastasis. Unlike blood vessels, lymphatics do not provide oxygen and nutrients that are essential for tumor growth. Why then do tumors induce lymphatic vessel growth? Do lymphatics play an active role in promoting tumor growth? Is tumor lymphangiogenesis secondary to blood vessel angiogenesis? How do tumors induce lymphangiogenesis? This review article focuses on discussing these fundamental issues related to cancer metastasis.