World's oldest cancer arose in a dog 11,000 years ago

London: Scientists have sequenced the genome of the world’s oldest continuously surviving cancer which first arose in an inbred dog about 11,000 years ago. The cancer, which causes genital tumours in dogs around the world, survived after the death of the dog by the transfer of its cancer cells to other dogs during mating. [caption id=“attachment_1357747” align=“alignleft” width=“380”]  Cancer carrier? AFP[/caption] The genome of the cancer—canine transmissible venereal tumor (CTVT)—carries about two million mutations—many more than are found in most human cancers, the majority of which have between 1,000 and 5,000 mutations. The team used one type of mutation, known to accumulate steadily over time as a “molecular clock”, to estimate that the cancer first arose 11,000 years ago. “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,” said Elizabeth Murchison, first author from the Wellcome Trust Sanger Institute and the University of Cambridge. The genome of the transmissible dog cancer still harbours the genetic variants of the individual dog that first gave rise to the cancer 11,000 years ago. Analysis of the genetic variants showed that the dog may have resembled an Alaskan Malamute or Husky. It had a short, straight coat that was coloured either grey/brown or black. Its genetic sequence could not determine if this dog was a male or a female, but did indicate that it was a relatively inbred individual. “We do not know why this particular individual gave rise to a transmissible cancer. 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,” said Murchison. “The patterns of genetic variants in tumours from different continents suggested that the cancer existed in one isolated population of dogs for most of its history. “It spread around the world within the last 500 years, possibly carried by dogs accompanying seafarers on their global explorations during the dawn of the age of exploration,” Murchison said. Cancer cells often spread to different parts of the body in a process known as metastasis. However, it is very rare for cancer cells to leave the bodies of their original hosts and to spread to other individuals. Apart from the dog transmissible cancer, the only other known naturally occurring transmissible cancer is an aggressive transmissible facial cancer in Tasmanian devils that is spread by biting. “The genome of the transmissible dog cancer will help us to understand the processes that allow cancers to become transmissible,” said Professor Sir Mike Stratton, senior author and Director of the Sanger Institute. PTI