How Contagious Tasmanian Devil Cancer Goes Invisible

Stephanie Pappas, LiveScience Senior Writer

A cancer that has wiped out 70 percent of wild Tasmanian devils became contagious by "switching off" certain genes that would otherwise enable the immune system to recognize it, a new study finds.

Devil facial tumor disease is one of only two contagious cancers in the world (the other affects dogs and is nonfatal). It spreads when the Australian marsupials bite or nip each other, transmitting cancerous cells that grow into enormous face tumors. The cancer either metastasizes to other organs or prevents Tasmanian devils from eating or drinking. Either way, death usually occurs within six months. Experts predict the species could vanish within 20 years if the tumor disease isn't stopped.

The immune system should catch these tumor cells, but the cancerous invasion causes no immune response in devils, said Hannah Siddle, a University of Cambridge immunology researcher. Siddle and her colleagues have now discovered why: The tumor cells lack surface molecules called major histocompatibility complex molecules. These MHC molecules allow the immune system to detect the invading cells. Without them, the cancer is essentially invisible.

Cotinued:  http://www.livescience.com/27804-contagious-devil-tumor-disease.html