Scientists who sequenced the genome of the world's oldest cancer say their
findings reveal the origin and evolution of the disease.
The transmissible genital cancer affects dogs, and it first appeared in a
single dog that lived about 11 000 years ago. The cancer survived the death of
that first host because the dog transferred cancer cells to other dogs during
mating, according to the researchers.
animal mating habits
The genome of this cancer – which causes genital tumours on dogs around the
world – has about 2 million mutations. That's many more than are found in most human
cancers, which typically have between 1 000 and 5 000 mutations.
Genome still alive
"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," study author Dr
Elizabeth Murchison, of the Wellcome Trust Sanger Institute and the University
of Cambridge in England, said in an institute news release.
The researchers also discovered that the genome of this cancer still contained
genetic variants of the first dog to have the cancer. The dog likely had a
short, straight coat and was either grey/brown or black. It may have resembled
an Alaskan Malamute or Husky. It's not known if the dog was a male or female,
but it was relatively inbred.
"We do not know why this particular individual [dog] gave rise to a
transmissible cancer," Murchison said. "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."
Transmissible cancers very rare
According to study senior author Sir Mike Stratton, director of the Sanger
Institute, "the genome of the transmissible dog cancer will help us to
understand the processes that allow cancers to become transmissible."
He explained in the news release that "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
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