Tumor cells have several routes that enable them to move from the primary tumor to distant tissues, a process called metastasis. It is metastasis of the primary tumor that kills most cancer patients. One of the least studied routes of metastasis is the lymphatic system. Many tumors produce factors that promote the formation of new lymphatic vessels (lymphangiogenesis). The newly formed lymphatic vessels enable tumor cells to travel from the primary tumor to the regional lymph nodes from whence they can spread throughout the body.