Contagious Cancer in Dogs Confirmed; Origins Traced to Wolves Centuries Ago
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CAMBRIDGE, Massachusetts, August 10/PRNewswire/ --
A new study in the August 11, 2006 issue of the journal Cell provides evidence that a form of cancer afflicting dogs has spread from one individual to another by the transmission of the tumor cells themselves. The disease demonstrates how a cancer cell can become a successful parasite with a worldwide distribution, according to the researchers.
Robin Weiss of University College London and his colleagues traced the origin of so-called canine transmissible venereal tumor (CTVT) to a single clone. They estimated that the parasitic cancer arose at least 200 years ago in either a wolf or a closely related ancient dog breed. That makes the tumors the oldest cancer known to science, and possibly the longest continually propagated mammalian cell lineage in the world.
"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."
CTVT, also known as Sticker's sarcoma, is apparently transmitted among dogs through sexual contact but may also spread through licking, biting and sniffing tumor-affected areas, the researchers said.
In the current study, the researchers applied forensic science to the study of CTVT, systematically examining tumor and blood samples from 16 unrelated dogs in Italy, India and Kenya. They also examined tumor samples taken from animals in Brazil, the U.S., Turkey, Spain and Italy.
They quickly found that DNA isolated from the tumor and blood samples were not a match.
The researchers traced the origin of the CTVT cancer by comparing the sequences of tumor genes to the related genes of gray wolves and dogs. Based on genetic variation among the very similar CTVT samples, the researchers estimated that the disease has been transmitted among dogs for two centuries or more.
The findings in CTVT might lead to new insights for cancer more generally, they said.
Although difficult to study, Weiss said that the possibility of sexually transmitted tumors-for example, prostate or cervical cancer--may have merit in humans, particularly among people with compromised immune systems such as organ transplant recipients and those with AIDS. In humans, occult tumors in donor organs have been known to emerge on rare occasions in immunosuppressed transplant recipients, Weiss noted.
