Unusual tumor is contagious in dogs.

A type of cancer in dogs is transferred from animal to animal by the exchange of cancer cells, a new study suggests. The results add credence to unusual reports that certain cancers can pass between animals within a species, most notably in Tasmanian devils (SN: 2/4/06, p. 67).

Canine transmissible venereal tumor (CTVT) appears most often in stray dogs. As the name implies, it's considered contagious. However, because cancer generally isn't transmissible, scientists puzzled over the identity of the infectious agent. Some researchers have suspected that a cancer-causing virus plays a role.

To investigate CTVT'S cause, Robin Weiss of University College London and his colleagues took tumor and blood samples from 16 dogs identified with the disease. The dogs came from three continents.

They found that in no dog did the tumor's DNA match that in the animal's blood. However, tumor DNA was identical from dog to dog. It also matched the DNA of 40 other CTVT samples stored in veterinary schools on five continents, suggesting that bits of the same tumor had circulated and grown in dogs around the world.

Further examination suggested that the tumor arose at least 200 years ago in a gray wolf or another dog-related species, Weiss' team reports in the Aug. 4 Cell. Some quality of that tumor enabled it to be transferred between related species by sexual contact, licking, or biting, the group suggests.