A team of scientists led by the University of Cambridge’s Elizabeth Murchison have sequenced the genetic material of the canine transmissible venereal tumor (CTVT) and determined that the now-immortal cancer is approximately 11,000 years old.
Dogs are susceptible to this contagious variety of cancer, which researchers say is a mutating organism that arose from a single dog about 11,000 years ago. Because the tumor itself is the infectious agent — it is not genetically related to dog that hosts it — scientists consider it a unicellular organism with an asexual mode of reproduction.
From its genetic material, the scientists discovered that the transmissible tumor originated in a medium-to-large sized dog that looked like a present-day husky with a black or grizzled coat, and that lived in an isolated, highly inbred dog population.
The tumor began its life as a dog cell between 10,200 and 12,900 years ago, and its genome demonstrates that since that time, it has undergone over 1.9 million mutations. Despite this high number of past mutations, the scientists noted that tumor is now relatively stable. Sequences from dogs in Australia and Brazil reveal that about 95 percent of the mutations are shared, and possess almost identical cell make-ups.
“There’s not a lot of new evolution going on,” Murchison told The Scientist. “This tells us that cancers do have this potential to go on living for thousands of years and, given the opportunity, they can become a more stable entity than cancers we usually see in humans.”
Hannah Siddle, another member of the research team, said that “CTVT may represent an evolutionary ‘endpoint’ for a tumor. Perhaps the tumor has become perfectly adapted to its niche and is not under further positive selection.”
This is not the first time a transmissible tumor has evolved in the dog population. Tasmanian devils can catch devil face tumor disease (DFTD). In an interview with National Geographic, Murchison said that “[t]hese cancers break so many rules we thought we understood. For instance, they’re able to spread between hosts, and to exist and live in different hosts[.]”
Their functional immortality is similar to the infamous “HeLa” line of cervical cancer cells — named for their original host, Henrietta Lacks — except these tumors continue to thrive outside of carefully managed laboratory environments.
[“Dog Labrador Nature Of Water” on Shutterstock]