extremely rare form of contagious cancer that affects
only dogs and is spread via sexual contact likely arose
in a single Alaskan malamute or husky-type canine more
than 11,000 years ago, scientists say.
a paper published Thursday in the journal Science,
researchers sequenced the genome of tumorous cancer
cells from two living dogs located at opposite sides of
the planet and determined the genetic makeup of the
first, ancient dog to suffer the disease.
cancer, called canine transmissible venereal tumor, or
CTVT, is the oldest and most widely spread cancer on the
planet, according to study authors. Prior studies have
estimated the illness to be up to 70,000 years old.
disease, which often appears as a red, cauliflower-like
mass on the animalís genitals, began as a single cell
in a single dog. That cell somehow acquired a mutation
that caused it to begin making copies of itself. These
fast-reproducing cancer cells then managed to survive
the ancient dogís death by transferring to another dog
do not know why this particular individual gave rise to
transmissible cancer," said lead study author
Elizabeth Murchison, a genetics researcher at the
Wellcome Trust Sanger Institute and the University of
spread around the world within the last 500 years,
possibly carried by dogs accompanying seafarers on their
global expeditions during the dawn of the age of
exploration," she said.
cancerís genome revealed an extraordinary number of
mutations since the rogue cell first appeared ó
roughly 2 million, according to Murchison and her
colleagues. Mutation counts in human cancers are far
lower and range between 1,000 and 5,000.
based their conclusions on cancer cells taken from two
afflicted dogs ó an Australian Aboriginal camp dog and
an American cocker spaniel from Brazil.
comparing genetic variations in the tumor cells, as well
as the genome of the first disease-suffering dog,
researchers determined the illness arose about 11,368
years ago, in an inbred dog of undetermined gender.
wrote that it was most likely an ancient breed of dog,
as opposed to a wolf, and was probably akin to an
Alaskan Malamute or a husky. The animal, they said, was
likely of medium or large size with an agouti or solid
also determined that the two living dogs likely had a
common ancestor who existed 460 years ago, during a
period of great human exploration.
fact that the first dog who suffered the disease was
likely inbred provides a significant clue to the success
of the disease. Limited genetic diversity may have
"facilitated the cancerís escape from its hostsí
immune systems," authors wrote.
tumors are rarely metastatic, and most will regress
within a few months, leaving infected dogs with new
immunity, according to cancer geneticists Heidi Parker
and Elaine Ostrander, of the NIHís National Human
Genome Research Institute.
occurring transmissible tumors are extremely rare,"
the pair wrote in an accompanying perspectives piece.
"The only other known example is the Tasmanian
devil facial tumor disease (DFTD). Ö Unlike the canine
tumor, DFTD is highly virulent, metastasizes readily,
and is ultimately fatal."
devils are a small island species with little genetic
diversity and, therefore, have little chance of
developing new resistance to the disease.
neither cancer has the ability to spread to humans,
researchers said they warranted investigation. Mike
Stratton, the senior author of the dog cancer study and
director of the Sanger Institute, said such studies
helped scientists to understand the evolution of cancer
transmissible cancers are very rare, we should be
prepared in case such a disease emerged in humans or
other animals," he said.