The oldest tumor in the world is 11,000 years old and affects dogs all over the world. To survive all this time, it hides a secret: it is a transmissible cancer, that is, it jumps from one individual to another but not hereditarily or by virus. In the case of this particular tumor, it does so sexually, passing from one dog to another. Transmissible cancers are rare, especially in humans, but “tremendously interesting”, explains scientist José Tubío, and that is why he decided to direct his research career to studying the characteristics of this disease in different species. Mineco has just awarded him a grant of 177,000 euros through the State Program for the Promotion of R&D&I of Excellence to investigate this 11,000-year-old tumor for the next three years.
Specialized in cancer genomics, Tubío highlights that transmissible cancers in humans are sporadic and have an artificial origin, such as a transplant of diseased organs or a blood transfusion with leukemia, for example. In the case of animals, it occurs naturally, and is a very interesting field of study.
Before arriving at the University of Vigo in 2016, the Galician scientist was studying in Cambridge the transmissible cancer that affects the Tasmanian devil, which is seriously endangering the survival of the species. “The tumor affects the face and mouth and, since they are very aggressive animals, they transmit the disease by biting these parts during fights,” he explains and recalls that this cancer is recent, “it has only been recorded for 30 years.” The other best-known case of transmissible cancer is that of dogs, which, in contrast to that of Tasmanian devils, is the oldest in the world. “It originated around 11,000 years ago, when dogs were not domestic animals and were more like wolves,” notes Tubío, who adds that it is estimated that at that time they possibly lived in the area of Mongolia. “This tumor is much more interesting because it has a global distribution, is found all over the planet and affects all breeds of dogs,” and points out that it is a cancer that affects the genital area and is transmitted through cancer cells during intercourse.
The importance of transposable elements
The dating of this cancer was done through an evolutionary study in which the researcher himself also participated and which was published two years ago in the journal Science. 1000 samples were collected from all over the world and two were selected from very different areas: Brazil and Australia. Its genome was sequenced through evolutionary dating methodologies based on genomic changes of both cancers, which allowed an estimate of when it originated and it was possible to date it to 11,000 years ago.
The geneticist highlights that “the only way for a cancer to live so long is for it to be transmitted from one individual to another, otherwise it would die when the patient dies, which is what happens in the human species”. In this sense, he points out that the study will focus on analyzing how transposable elements behave, “DNA sequences that have the ability to move, to jump from one side to another”. As the scientist explains, in a normal cell the transposable elements are stationary, but when the cell becomes cancerous “these elements begin to jump and cause mutations that we think may be important in the origin or evolution of cancer in humans”.
Going deeper into this area will allow, according to Tubío, to find out what the relationship between cancer and the patient would be like over a very long period of evolution. “Questions arise about cancer in humans that we cannot answer unless we study this type of transmissible cancer and, to do so, we have a great model in this cancer in dogs, with 11,000 years of life”, since these transposable sequences are very similar to those of humans. He explains that “the sequences when they are mobilized are harmful to us, but for cancer they can be beneficial, since the more it mutates, the more it ensures its survival, it needs it to grow and evolve”. This happens “up to a limit”, because these mutations can end up killing the cancer, hence its importance for the study of human cancer. “To maintain itself over such a long time, we believe that a balance had to be reached, in which the transposable elements had to lower their aggressiveness and we do not see this balance between transposable elements and cancer among humans, but it can occur in an 11,000-year-old cancer,” emphasizing that knowing that intermediate point can help obtain a model of that balance in a human cancer if it could live that long.
Transmissible cancers in marine animals
This study, which will be developed over the next three years, will advance in parallel with other lines of research, mainly focused on the marine field. “My main line of work in the coming years will be transmissible cancer in marine animals, a line in which I want to specialize and which will serve to differentiate me from the rest of the researchers.” He emphasizes that while in other studies he depends on samples that must be provided by other universities and institutions, in the case of marine animals the University of Vigo has facilities that will allow him to make the project 100% Vigo-based, “and that is one of the reasons that made me come to Vigo,” he concludes. In fact, this new line is his bet for the ERC Starting Grant call, which will be resolved throughout the summer and in which he is among the finalists for this prestigious European grant.
