In studying a cancer found in dogs, researchers were able to establish that tumor cells can become parasitic and transmitted from one dog to another by way of sex, licking, biting or sniffing cancerous areas of an affected dog.

University College London researchers state they were able to trace back at least 200 years the origin of the first venereal tumor (CTVT) to a wolf or other ancient dog breed.

Not only does the discovery make this cancer, known as Sticker's sarcoma, the oldest cancer studied, as it has been continuously passed down for hundreds of years, it also allows scientists to gain a greater understanding of how cancer can progress.

"Our results, based on several independent genetic markers in tumor-bearing dogs living on five continents, show that CTVT arose from a common ancestral cancer cell," Weiss said. "The cancer escaped its original body and became a parasite transmitted from dog to bitch and bitch to dog until it had colonized all over the world." Early in its evolution, the clone diverged into two separate lineages, each of which now has a broad geographic range, explained Robin Weiss of University College London.

The study appears in the August 11, 2006 issue of the journal Cell.