About 11000 years ago, a dog got a tumour. One cell from that tumour became especially dangerous. It could leave its host organism (the dog) to infect another dog so it, too, grew cancer. And then the cell jumped again, infecting another dog, and that could be repeated endlessly. This cancer is still spread among dogs by sex or close contact.
The dogs die on the way, but the very same cancer is still alive after 11000 years! It is called CTVT, canine transmissible venereal tumour, or sometimes Sticker's sarcoma. It is a parasite, today present in the population of dogs on all continents. It is not only the oldest known cancer, it is also the oldest known somatic cell lineage.
Studies conducted at the University of Cambridge indicate that these cancers sometimes pick up new mitochondria from their hosts and that it would have happened 5 times – although nobody knows exactly how this happens. Thus there are 5 distinguishable lineages of CTVT.
While CTVT is about 11000 years old, none of the lineages are more than 1700 years old. These lineages reveal something about the history of dogs, which, hardly surprising, reflects the history of humankind. The cancer of dogs spread with human travelling. For example, one lineage of CTVT, widespread over the Eurasian continent, reached the Americas with the European colonisation of the Western Hemisphere.
Studies of contagious cancers might give us valuable knowledge of other cancers as well. But it also raises an interesting question about human cancers. Although scientific mainstream today holds that no human cancer is contagious (if we do not count the cancer spread or triggered by Human Papilloma Virus, but that is an entirely different mechanism), is this really true? And if it is, is there a risk that contagious human cancer suddenly develops in the future?
Whatever the answer to the first question, and I do have my doubts about the mainstream view, there is absolutely no reason to believe it impossible that a human cancer at any time in the future develops this ability to “jump”.
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