The other known contagious cancer is a sexually transmitted cancer that occurs in dogs. Known as canine transmissible venereal tumor (CTVT), this cancer has outlived the dog in which it first emerged by spreading its abnormal cells on to other dogs through mating. Researchers have now discovered that this cancer, which results in genital tumours, first arose in a single dog that lived about 11,000 years ago, making it the oldest known line of cancer cells.
The researchers, from Wellcome Trust Sanger Institute in the UK, came to this conclusion after they were able to decode the DNA of the cancer. They do not know how the cancer first emerged, but they have been able to learn that the animal in which it first appeared was an ancient husky-like dog of medium size with a short, straight coat that was grey-brown or black in colour.
According to findings of the research, published in Science, the cancer has been able to survive despite undergoing millions of genetic changes. In all, there have been about two million mutations. Human cancers in comparison usually have between 1,000 and 5,000 mutations. For a long period, the cancer existed in an isolated population of dogs. It then rapidly spread in the last 500 years, which according to the researchers was perhaps caused by dogs accompanying explorers on sea voyages.
The research shows how, given the right conditions, cancers can spread and continue to survive for many years. According to the researchers, this work will help them understand how cancers turn transmissible.
One of the authors of the study, Professor Sir Mike Stratton, said in a press release: ‘Although transmissible cancers are very rare, we should be prepared in case such a disease emerged in humans or other animals. Furthermore, studying the evolution of this ancient cancer can help us to understand factors driving cancer evolution more generally.’