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A Dog's Cancer

Some 11,000 years ago, a dog developed a tumor that some how became transmissible, spreading from dog to dog through mating or other close contact, the Economist writes. But since the rise of that first canine transmissible venereal tumor, the disease has — a few times — acquired bits of mitochondrial DNA from its hosts, and researchers from the University of Cambridge and elsewhere have used that to study the migration of dogs across the globe.

As they report in eLife this week, Cambridge's Elizabeth Murchison and her colleagues sequenced the mtDNA from nearly 450 CTVTs and matched hosts from around the world to find that such instances of horizontal transfer have occurred at least five times. Through this, they uncovered five tumor clades, two of which have global distributions and are the most common clades. Early diverging tumors in one of those clades were found in Russia, Ukraine, China, and India, which indicated to the researchers that this clade's origins are in the Old World. Further, tumors belonging to that clade from Central and South America shared a common ancestor some 500 years ago, indicating CTVT arrived in the Americas with colonists.

Since these mtDNA swaps have repeatedly occurred, Ed Yong at Not Exactly Rocket Science writes that they may offer an advantage for the cancer — and could be occurring in human cancers.

"If so, blocking the process could provide another way to fight the disease," he Economist adds. "That would be one more debt man owes to his dogs."