Azra posted this a couple of days ago at 3QD. Carl Zimmer has more thoughts about it in his blog, The Loom:
Can a tumor become a new form of life?
This is the freaky but serious question that arises from a new study in the journal Cell. Scientists from London and Chicago have studied a peculiar cancer that afflicts dogs, known as canine transmissible venereal tumor (CTVT) or Sticker’s sarcoma. It is a cancer of immune cells called histiocytes, and dogs typically develop grapefruit-sized tumors that disappear after a few months…
So here’s the big question which the authors don’t tackle head on: what is this thing? Is it a medieval Chinese dog that has found immortality? If so, then it resembles HeLa cells, a line of cancer cells isolated from a woman named Henrietta Lacks who died in 1951. After her death, scientists have propagated her cells, and in that time they have have adapted to their new ecological niche of Petri dishes, acquiring mutations that make it grow aggressively in the lab. One biologist even suggested that the cells should be consider a new species.
Sticker’s sarcoma has, without any intervention from scientists, become a cell line as well, and one that has survived far longer than HeLa cells have. It is distinct from its dog ancestors, and has acquired adaptations that allow it to manipulate its hosts for its own advantage as effectively as a virus or a blood fluke. A parasite evolved from a dog, perhaps.
More here.