A new study has shown that an infectious cancer in dogs is 11,000 years old. The strain is still in its exact form for this remarkable amount of time because it is contagious and transferrable unlike other cancers. The cancer is spread from animal to animal during physical contact like licking and breeding.
There are only three types of known contagious cancers and canine transmissible venereal tumor (CTVT) is one of them studied by Elizabeth Murchison who is a researcher at the Department of Veterinary Medicine at the University of Cambridge. Murchison led the study and authored the new analysis that was published in Thursday’s issue of Science, where she calls this type of cancer a parasite.
The study tried to understand how this cancer spread as it is unusually resilient. The cancer was traced in origin from studying dogs from all over the world. As an example, tumor cells were taken from a dog from an Aboriginal camp in Australia and they were compared to a CTVT infected American cocker spaniel from Brazil.
After analyzing data, the researchers were able to determine that the mother or father of the cancer type was first seen in a large or medium dog possibly related to a husky or Alaskan malamute. The researchers were also able to tell that the parent of the cancer had a dark or agouti coat and a pointy nose and ears.
The contagious and transferrable cancer starts as rogue cell growth that is triggered by the animal’s mutations. Usually the cancer cells are destroyed when passed to a new host, but CTVT can sometimes bypass the animal’s defenses to grow infectious tumors in their new host’s sexual organs. Murchison called CTVT a “super cancer” as it has survived in the same strain for thousands of years spreading from dog to dog.
The research suggests that humans are partly to blame for the spreading of CTVT as the domestication of the dog has enabled the cancer to spread. Dogs started to interact with other domesticated dogs and their human masters. These early domesticated pets were incredibly inbred according to Clare Rebbeck who researches CTVT independently at New York’s Cold Spring Harbor Labs. Rebbeck suggests that the inbreeding of these animals is responsible for CTVT’s odd mutations. Rebbeck said that the limited interaction from the inbred dogs would have allowed CTVT to develop.
Up until late, scientists theorized that CTVT was being spread by a bacteria or virus. However in 2006 researchers found that the cells from the dog’s tumors were the actual source of the cell’s contagious nature.
Another type of cancer that is contagious is a human equivalent of CTVT is named HeLa. Cells from a HeLa patient, Henrietta Lacks, were taken in 1951 and live on in labs across the globe. However CTVT has lived for around 11,000 years unassisted by any lab researchers and has multiplied all by itself.
The third type of contagious cancer is a lethal face cancer that is currently threatening Tasmanian devil populations. The face cancer has only been in known to exist for the last 30 years, but the researchers feel that the disease started in the Tasmanian devil population for the same reason. The area in which the face cancer is found contains Tasmanian devil populations that are very isolated on an island and inbreeding is more common.
In CTVT, only one X chromosome has been found to have survived over many generations making it tough to peg the sex of the first canine to carry the disease. Over the many millenniums CTVT has collected roughly two million mutations while tumors in humans are known to collect only a few thousand. Murchison believes that the secret to how long the line of cancer has existed is likely to be among those mutations. Finding the mutations that are responsible for the cancer’s resilience is the next part of the CTVT study. Murchison really wants to know how CTVT is able to evade the dog’s immune system.
CTVT does respond well to an infected dog having chemotherapy because the cancer lacks the diversity to adapt to the animal’s treatments. Inversely, tumors in people tend to have many different types of cancer cells that compete against each other which eventually lead to the cancer cells ability to adapt to human cancer treatments.
Murchison’s next stage in the study of the contagious and transferrable cancer in dogs is finding out what location on the globe the infectious CTVT originated in.
By Brent Matsalla