Metastasis in the Light

Abstract

Cancer![Figure][1] CREDIT: © RISAMAY/ISTOCKPHOTO Cutaneous melanoma is less common than other forms of skin cancer but is far more deadly, especially if not detected at an early stage. Ultraviolet (UV) light from the Sun plays a key role in the initiation of melanoma by inducing mutations in the DNA of melanocytes, the pigment-producing cells in skin. A new study suggests that UV light does damage well beyond this early role: It appears to trigger a chain of pathologic events that facilitate metastasis. Studying a mouse model, Bald et al. found that repetitive exposure of primary melanomas to UV light did not increase tumor incidence or growth but rather increased the number of lung metastases. Closer examination revealed that UV light induced the recruitment of certain immune cells (neutrophils) to the primary tumor. This inflammatory response in turn activated endothelial cells (cells that line blood vessels) and triggered migration of the melanoma cells toward them, resulting in the expansion of tumor cells along blood vessels. This “angiotrophic” growth pattern is thought to increase the likelihood that tumor cells enter the bloodstream and metastasize. Consistent with this, human melanoma samples with high levels of neutrophils were more metastatic. Nature 10.1038/nature13111 (2014). [1]: pending:yes