Ancient cancer has been spreading among domesticated dogs for the past 6,000 years

There is a type of cancer that is spreading among dogs that is one of the oldest cancer known by humans. It might have first originated in Asia or Europe, around 6,000 years ago. It has somehow survived the death of the first dog – patient zero – and has spread around the world. The cells of this cancer are the same as the first dog that had it and not the carrier dog. The only differences that have come about in these cells are those that have come about naturally in the cells or changes that have taken place in the cells’ DNA due to carcinogens (any substance that promotes the formation of cancer). This cancer usually manifests itself in domestic dogs, both male and female, in the form of genital tumours. [caption id=“attachment_7100771” align=“alignnone” width=“1280”] There is an ancient type of cancer in dogs that has spread from Asia or Europe.[/caption] Adrian Baez-Ortega, a researcher in the study said in a press release, “This tumour has spread to almost every continent, evolving as it spreads. Changes to its DNA tells a story of where it has been and when, almost like a historical travel journal.” The researchers collected cancers from 546 dogs all over the world to conduct this study. They created a phylogenetic tree (a tree that shows the descent or relationship of species). It showed the different mutations among the tumours. This tree showed them that the cancer is extremely old and first came up 4,000-8,500 years ago in either Asia or Europe. The cancer spread from Europe to the Americas when the settlers arrived there and all the tumours found here can be traced to this single event. It then moved throughout the European colonies all over the world. [caption id=“attachment_7100761” align=“alignnone” width=“1000”] Canine cancer spread to the Americas around 500 years ago and then subsequently through European colonies. Image credit: University of Cambridge[/caption] What’s interesting to the study is how the tumours caused by this cancer evolves. There are two main types of selections in the evolutionary theory – positive and negative evolution. Positive selection is when the mutations that provide an organism with a particular advantage are passed down to the next generations. Negative selection is where mutations that are likely to have a negative effect are less likely to be passed on. Such selection tends to occur by way of sexual reproduction. However, there is no positive or negative selection in these tumours. This means that the cancer is collecting damaging mutations over a period of time and hence it will soon not fit into its environment i.e. the dog’s bodies. Baez-Ortega explains in the statement, “This cancer ‘parasite’ has proved remarkably successful at surviving over thousands of years, yet is steadily deteriorating. It suggests that its days may be numbered – but it’s likely to be tens of thousands of years before it disappears.” Researchers from the University of Cambridge’s Transmissible Cancer Group conducted the research and the  findings from this study has been published in the journal Science.