Tasmanian Devils, the real-life marsupial inspiration behind the cartoon beastie, were already an endangered species when nature added insult to injury. In 1996, researchers first formally described Devil Facial Tumor Disease, a cancer that would later turn out to be contagious, passed from devil to devil by biting, mating, and sharing food.
While you're probably familiar with the idea that viruses can cause cancer, that's not what's going on here. Instead, the cancer cells themselves are contagious. It's a rare phenomenon, but not (terrifyingly enough) completely unique. At Nature blogs, Anne-Marie Hodge writes about other cases of contagious cancers in mammals.
One prime example is canine transmissible venereal tumor (CTVT), a histiocytic tumor that is passed between dogs through sex as well as sniffing and licking of the genitals. At one point it was thought that a sexually transmitted virus, similar to HPV, caused this disease. It turns out, however, that it is the CTVT cells themselves that are infectious, not a virus that activates them. The cancerous cells themselves, which are essentially clonal, are what is passed from animal to animal.
For example, when an infected Dog A has genital contact with Dog B, what is transmitted is not some agent (such as a virus) that triggers Dog B's cells to start dividing and creating tumors. Instead it is the cancer cells themselves, which are genetically different from both Dog A and Dog B, which continue to clone themselves on their new victim. Thus it seems animal that receives CTVT from its mate is not so much infected as colonized, and that is why CTVT is sometimes referred to as a "parasitic cancer." The tumors most often appear on the external genitalia, but may also affect the nose and mouth.
There are few interesting aspects of CTVT cells. While normal dog and wolf cells contain 78 chromosomes, the tumor cells have fewer, usually between 57-64, and even those chromosomes bear some distinct morphological differences from those found in healthy dog tissue. The disease also infects coyotes (which also have 78 chromosomes) and red foxes (with only 34 chromosomes).
Via Bora Zivkovic