Contagious Dog Cancer Unraveled

- A contagious cancer in dogs has the ability to repair itself by acquiring mitochondria from its canine host's cells.

- The discovery could help to explain how this cancer, CTVT, has remained in the dog population for around 10,000 years.

- It's hoped that future research may lead to preventions or cures for other transmissible cancers.

Dogs can suffer from a contagious form of cancer that has the ability to repair itself at the expense of its canine victims, according to a new study.

The discovery could help to explain how this disease, Canine Transmissible Venereal Tumor (CTVT), has persisted in the dog population for around 10,000 years. Mating in dogs typically transmits the cancer, although it can also be spread when a healthy dog licks, bites or sniffs tumor-affected areas of a victim.

"It is possible that when dogs were first domesticated, they were highly inbred, and so different individuals were genetically very similar, and this might have helped cancerous cells from one dog to be able to grow on another." study co-author Austin Burt told Discovery News.

"Then, as dogs were bred in many different directions and became genetically diverse, the cancer would have evolved to be able to grow on a diverse array of genotypes," added Burt, a professor of evolutionary genetics at Imperial College London.

He and colleagues Clare Rebbeck and Armand Leroi analyzed the cellular structure of a geographically diverse sample of CTVT samples. They noticed that the cancer would sometimes acquire the "powerhouses," or mitochondria, of host cells in order to repair itself in response to accumulated genetic mutations.  

To determine if this was really the case, the scientists studied the evolutionary development of dogs and wolves. That investigation further supported their determination about the host-hijacking cancer. The research was published in this week's Science

The disease is known to only spread from one canine to another, and "feral dogs -- ones that run wild -- are the ones most likely to come into contact with the cancer and carry it," according to Burt.

"In the lab it can be experimentally transmitted to foxes, but we are not aware of any evidence of it transferring naturally to any other species," he said.

Both he and the American Cancer Society state that no form of human cancer is contagious. In informational literature, the American Cancer Society points out that certain germs can affect cancer risk and play a role in the development of some types of cancer, but the society quickly adds that "a healthy person cannot 'catch' cancer from someone who has it."

It is unclear if the new findings about cancer's ability to repair itself could apply to human cancer and to contagious cancers throughout the animal kingdom.  

One such cancer, Devil Facial Tumor (DFT) disease, which affects Tasmanian devils, is of particular concern. So many of these animals have died from the disease in recent years. In 2009, Tasmanian devils were listed as being endangered. Researchers are struggling to find better treatments and a possible cure for DFT, hoping to prevent Tasmanian devils from becoming extinct.

Burt said CTVT and DFT "are both transmissible cancers. CTVT is less likely to be fatal than devil facial disease," which is primarily transferred during fights.

Robin Weiss, a professor of viral oncology at University College London, told Discovery News he doubts the new research will lead to further cancer medical breakthroughs, but he thinks the study presents "a delightful snippet of evolutionary biology."

The good news about CTVT is that it can often be successfully treated with drugs.

Burt said, "Also, many times the cancer is eventually recognized by the dog immune system and the dog recovers without treatment."