The genome of the world's oldest continuously surviving cancer - an 11,000-year-old genital cancer in dogs that can be transmitted during mating - is helping scientists understand underlying factors that drive cancer evolution in general.
The latest study, in which researchers describe the genome and evolution of the cancer, has been published in the journal Science.
They note that cancer normally lives and dies with a single person. There is no need to panic, however, as there is currently no known transmissible cancer in humans.
But in dogs, one ancient cancer can be caught from another dog, causing genital tumors.
The genome of this cancer carries around 2 million mutations, the researcher say. This is many more than those found in human cancers, which usually have between 1,000 and 5,000 mutations.
Using one type of mutation that is known to accumulate gradually over time, the researchers created a "molecular clock" to determine that the cancer first came about 11,000 years ago.
Dr. Elizabeth Murchison, study author from the Wellcome Trust Sanger Institute and the University of Cambridge in the UK, says:
"The genome of this remarkable long-lived cancer has demonstrated that, given the right conditions, cancers can continue to survive for more than 10,000 years despite the accumulation of millions of mutations."
Interestingly, the genome of this cancer still carries with it the genetic variants of the original dog in which the cancer arose. The team says these variants show that the dog may have resembled an Alaskan malamute or husky.
They add that it likely had a short, straight coat with a gray/brown or black coloring. Though the sequence could not determine whether the dog was male or female, it did reveal that it was inbred.
Understanding factors driving evolution of cancer
In both humans and animals, cancers crop up when just one cell in the body mutates and produces more copies of itself. Though cancers can spread to different parts of the body through metastasis, the researchers note that it is very rare for cancer cells to leave the body of the original host and spread to others.
The researchers determined the 11,000-year-old transmissible cancer originated in a dog resembling a husky or Alaskan malamute, pictured here.
The only other known transmissible cancer exists in Tasmanian devils as a facial cancer, which is spread by biting.
Genetic variant patterns in tumors from around the world suggest that the dog cancer spread globally within the last 500 years, "during the dawn of the age of exploration," says Dr. Murchison.
The researchers say they do not know why the transmissible cancer arose in the original dog. "But it is fascinating to look back in time and reconstruct the identity of this ancient dog whose genome is still alive today in the cells of the cancer that it spawned," says Dr. Murchison.
And studying this genome sequence is helping the researchers understand how the disease was spread and how cancers become transmissible.
Prof. Mike Stratton, lead author and director of the Sanger Institute, says:
"Although transmissible cancers are very rare, we should be prepared in case such a disease emerged in humans or other animals. Furthermore, studying the evolution of this ancient cancer can help us to understand factors driving cancer evolution more generally."
In 2013, Medical News Today reported on a study suggesting that there are a potential 320,000 undiscovered mammal viruses. The researchers suggested that uncovering these viruses could be critical for early detection and developing cures for disease outbreak in humans.