Paving the way to metastasis

Tumors must invade lymph nodes to become metastatic, but how the tumor cells make this trip is not completely clear. On page 1089, Hirakawa and colleagues show that a tumor-derived growth factor stimulates the formation of new lymphatic vessels in the nearby lymph node, even before any tumor cells arrive. This suggests that the tumor may instruct the lymph node to prepare for its arrival.

Stimulation of lymphatic growth has for some time played second fiddle to angiogenesis. During angiogenesis, tumors produce factors such as vascular endothelial growth factor-A (VEGF-A) that induce vessel growth and thus greater nutrient supply. Recently, however, two relatives of VEGF-A, VEGF-C and VEGF-D, have been shown to induce lymphangiogenesis within tumors. Although earlier studies suggested that VEGF-A could also induce lymphangiogenesis, this had...