Cancer as parasite is an analogy I’ve been aware of, but I’ve never seen a cancer spreading between animals as a direct parasite (generally contagious spread is a result of viral hijacking causing changes in DNA that then leads to cancer).

Interesting — and potentially a disruptive way to think about cancer biology.

Scientists Report Findings on Origin of a Cancer in Tasmanian Devils – NYTimes.com.

The Tasmanian devil, the spaniel-size marsupial found on the Australian island of Tasmania, has been hurtling toward extinction in recent years, the victim of a bizarre and mysterious facial cancer that spreads like a plague.

Now Australian scientists say they have discovered how the cancer originated. The finding, being reported Friday in the journal Science, sheds light on how cancer cells can sometimes liberate themselves from the hosts where they first emerged. On a more practical level, it also opens the door to devising vaccines that could save the Tasmanian devils.

The cancer, devil’s facial tumor disease, is transmitted when the animals bite one another’s faces during fights. It grows rapidly, choking off the animal’s mouth and spreading to other organs. The disease has wiped out 60 percent of all Tasmanian devils since it was first observed in 1996, and some ecologists predict that it could obliterate the entire wild population within 35 years.

When the tumor disease was discovered, many scientists assumed that it was caused by a rapidly spreading virus. Viruses cause 15 percent of all cancers in humans and are also widespread in animals.

But subsequent studies failed to turn up a virus. Instead, Anne-Maree Pearse and Kate Swift, of the Department of Primary Industries, Water and Environment in Tasmania, discovered something strange about the tumor cells. The chromosomes looked less like those in the animal’s normal cells and more like those in the tumors growing in other Tasmanian devils.

In 2007, Dr. Belov and her colleagues compared DNA from 26 sick and healthy Tasmanian devils with DNA from the tumors. They found that cancer cells from different animals shared distinctive genetic markers not found in the animals themselves.