World-Traveling Canine Cancer Traced Back Thousands of Years

(CN) – A study published Thursday in the journal Science finds a widespread canine cancer, mainly spread during mating, may kill itself off over tens of thousands of years.

Found in dogs on almost every continent, canine transmissible venereal tumor has the oldest lineage of cancer in nature. But its DNA is deteriorating.

“[W]e demonstrate how evolution can turn a cancer into a relatively mild disease – more akin to a parasitic infection – and, moreover, how this arrangement seems to be sustainable in the long term,” said first author Adrian Baez-Ortega, of University of Cambridge’s Department of Veterinary Medicine, in an interview.

Unlike human cancers, CTVT is easy to treat with chemo or radiotherapy and does not usually develop resistance. However, Baez-Ortega notes that the findings support “adaptive therapy” approaches, which apply “knowledge about evolution and ecology” to prolong human lives by making cancers manageable.

CTVT usually presents as genital tumors and spreads when live cancer cells transfer from one dog to another. Researchers studied the genomes of 546 afflicted dogs around the world.

Baez-Ortega called the deep dive into the dogs’ DNA a “historical travel journal.”

A big surprise: Data suggest the cancer started 4,000 to 8,500 years ago, yet today’s tumors have cells from the first dog – or founder – in which the disease arose.

Another surprise: Exposure to UV light and at least four other carcinogens has damaged the canine tumor over time.

“Two of these biological processes are similar to those found in normal human cells and correspond to spontaneous molecular processes that cause mutations in every cell, not just cancer cells,” said Baez-Ortega. A third, she added, is “linked to the disregulated action of certain enzymes, but we are not entirely sure about this.”

One of five processes was active several thousand years ago and then was not.  “It’s a mystery what the carcinogen could be,” said a statement from Elizabeth Murchison, corresponding author and leader of Cambridge’s Transmissible Cancer Group.

CTVT has recorded the “changing mutagenic environments” where it has traveled over centuries. It likely spread by ships carrying explorers, pirates, navies, settlers, merchants and their dogs.

The cancer arrived in the Americas about 500 years ago, when Europeans spread to the continent. Tumors studied in North, Central, and South America were traced to that European settlement. CTVT then spread to Africa and back to the subcontinent of India.

Canine cancer spread to the Americas around 500 years ago and then subsequently through the European colonies. (Adrian Baez-Ortega)


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