The genome of this 11,000-year-old cancer carries about two million mutations - many more mutations than are found in most human cancers, the majority of which have between 1,000 and 5,000 mutations.
"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 from the Wellcome Trust Sanger Institute and University of Cambridge, Britain.
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.
Analysis of these genetic variants revealed that this dog may have resembled an Alaskan Malamute or Husky.
It probably had a short, straight coat that was coloured either grey/brown or black.
"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," informed Murchison.
Transmissible dog cancer is a common disease found in dogs around the world today.
The genome sequence has helped scientists to further understand how this disease has spread.
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, said the study.
"The genome of the transmissible dog cancer would help us understand the processes that allow cancers to become transmissible," said Mike Stratton, senior author and director of the Sanger Institute.