This article was originally published in 2019. The research was supported by Wellcome, the Leverhulme Trust and the Kennel Club Charitable Trust.The director explains his coda: “I thought it was being real and honest with the audience.” It suggests that its days may be numbered – but it’s likely to be tens of thousands of years before it disappears.” “This cancer ‘parasite’ has proved remarkably successful at surviving over thousands of years, yet is steadily deteriorating. These canine tumours are foreign bodies, so one would expect to see a battle between them and the dog’s immune system, leading to only the strongest tumours successfully being transmitted. This implies that the tumour will be accumulating more and more potentially damaging mutations over time, making it less and less fit to its environment.īaez-Ortega explains: “Normally, we see selection pressures acting on an organism’s evolution. When the researchers analysed the tumours, they found no evidence of either positive or negative selection. Such selection tends to occur by way of sexual reproduction.

Positive selection is where mutations that provide an organism with a particular advantage are more likely to be passed down generations negative selection is where mutations that are likely to have a deleterious effect are less likely to be passed on. There are two main types of selection in evolutionary theory – positive and negative. Perhaps it was something present in the environment where the cancer first arose.”Īnother intriguing discovery related to how the tumours evolve. It’s a mystery what the carcinogen could be. “It looks like the tumour was exposed to something thousands of years ago that caused changes to its DNA for some length of time and then disappeared.

“This is really exciting – we’ve never seen anything like the pattern caused by this carcinogen before,” says Dr Elizabeth Murchison, who leads the Transmissible Cancer Group at the University of Cambridge.

However, one of them – termed ‘Signature A’ – has a very distinctive mutational signature, different to any seen previously: it caused mutations only in the tumour’s distant past, several thousand years ago, and has never been seen since. Four of these, including exposure to UV light, are known processes already linked to human cancers. Using these techniques, the researchers identified signatures for five different biological processes that have damaged the canine tumour over its history. This allows them to see, for example, the damage that ultraviolet (UV) light causes. Recent developments in cancer biology have enabled scientists to look at the mutations in tumour DNA and identify unique signatures left by carcinogens. While the findings related to the historical spread of the disease are interesting, it is the tumour’s evolution that particularly excites the researchers.

Parasite in the city deaths