Under extreme circumstances, cancer can be contagious. The biologist José Tubío recalls the case of a German surgeon who sustained a small wound in his left hand while removing a malignant tumor. Five months later, the patient’s cancer had grown on the doctor’s finger. In Japan, two children suffered from lung tumors that arose from uterine cancer cells that their mothers had on the day of delivery. It is estimated that only one in 500,000 mothers with cancer transmit the cancer to their children through the placenta. In molluscs, explains Tubío, transmissible cancer is much more common. In one can of cockles there can be several specimens suffering from leukemia, which are equally tasty and safe to eat. It is not a cancer that arises in each individual, but rather cancer cells from the same distant tumor that have been jumping from cockle to cockle through the sea for thousands of years. Tubío, from the University of Santiago de Compostela, believes this phenomenon can help understand metastasis, which accounts for 90% of cancer deaths in humans.
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The biologist, who was born in Santiago 45 years ago, was among the scientists who discovered a new type of infectious facial tumor in the Tasmanian devil in 2014. This carnivorous Australian marsupial, popularized by Warner Bros. cartoons, was already threatened by another transmissible cancer observed nearly a decade earlier. The discovery of a second type suggests that transmissible tumors are more common in nature than previously thought. Devils transmit cancer cells through contact, particularly through bites during fights or during copulation. The cancer grows and deforms the animal’s snout until it can no longer eat and dies.
The Tubío team traveled along the European and Moroccan Atlantic coasts in search of cockles with leukemia. The researchers sent them alive by express mail or transported them themselves by plane or in the trunk of the car to their laboratory at the University of Santiago de Compostela. The group analyzed about 7,000 cockles, nearly 6% of which had cancer. According to Tubío, the results were “a shock”. The genetic information of animals is grouped into packages: chromosomes. These mollusks normally have 38, but their cancer cells reach 350 and they are also very degraded. “You find completely different sets of chromosomes in human tumors, but the level we saw in cockles is extremely unstable. How is it possible that a tumor can survive for thousands of years despite this enormous chaos in its genome? It’s a new paradigm,” says the biologist.
Vaccination of an infectious leukemia in a cockle at the University of Santiago de Compostela.USC
The scientific community has already discovered 11 types of transmissible cancer: eight in bivalves – such as mussels, cockles and mussels – two in the Tasmanian devil and another in dogs. Tubío has also studied this venereal tumor in dogs, which spreads and grows in the genital area during copulation. The biologist emphasizes that these are cells from a certain dog that developed cancer around 8,000 years ago and has been multiplying and jumping from individual to individual ever since.
Tubío believes that cockle cancer is “certainly the oldest known transmissible cancer.” Their study, published in the journal Nature Cancer, suggests that these tumors originated “centuries or millennia ago.” Biologist Michael Metzger’s group from the Pacific Northwest Research Institute (USA) publishes another parallel paper that estimates that the New England clam is at least 200 years old. “Both tumors are probably ancient,” says Tubío. The researcher points out that the cancer cells in cockles are so different from normal ones that his team came to believe that this tumor came from an extinct species. “Eventually we concluded that it originated in a cockle of the same species thousands of years ago. We have some estimates that suggest the age of this tumor is between 100,000 and half a million years, but this requires a more thorough investigation,” he emphasizes.
Biologists Alicia L. Bruzos and Seila Díaz spent months searching for cockles with leukemia on beaches along with other colleagues. Bruzos is used to strange looks when she explains what she does, but she counters with the names of scientists who won the Nobel Prize in Medicine for studying marine animals. Ukrainian Elie Metchnikoff received the award in 1908 for discovering phagocytosis – the process by which white blood cells destroy a foreign substance – after stinging starfish larvae with rose thorns. Britons Alan Hodgkin and Andrew Huxley revealed the electrical mechanisms of neurons by studying squid and won the Nobel Prize in 1963. And the Briton Tim Hunt discovered proteins in sea urchins that are important for cell division. He received the award in 2001.
Bruzos, now at the University of Caen (France), devoted his doctoral thesis in Santiago de Compostela to cockles with leukemia. “I don’t want to say that this is Nobel Prize research or that research into cockle tumors will cure cancer, but there are many things that we know today that have been discovered through research into rare animals or plants. ” explains the biologist born 30 years ago in Lugo. “A contagious cancer is a cancer that can be transmitted from one person to another person. It seems like science fiction, but if we think about it, the main problem with cancer In our society today, metastasis occurs. And metastases occur when one or more cells of the primary tumor acquire the ability to migrate to other parts of the body. The analogy is quickly apparent. When we find out which molecular mechanisms enable a cell to leave an individual and to reach another, in this case by sea, that can help us develop ideas for new strategies to try to cure the metastasis of a normal cancer,” says Bruzos.
The biologist José Tubío in his office at the University of Santiago de Compostela. Iria Diaz (USC)
Biochemist Óscar Fernández Capetillo studies the molecular peculiarities that lead to cancer at the National Cancer Research Center (CNIO) in Madrid. “Science is fascinating when the question is interesting, even if it is asked at crickets,” defends this specialist, who was not involved in the new work. “Studying the genome of transmissible tumors is a very interesting task that deals with the origins of cancer and how a tumor that has existed for a long time eventually accumulates mutations that allow it to become authentic chromosomal Frankensteins with a gigantic number of chromosomes,” he emphasizes. “This tumor originated in one cockle, which passed it on to another cockle, which then passed it on to another cockle. “It’s like a tumor that has had 1,000 lives.”
Fernández Capetillo, head of the CNIO Genomic Instability Group, has in his laboratory cancer cells from human tumors with more than 150 chromosomes, compared to the usual 46. “I believe that the mechanisms that explain why the genome of a cockle changes so much , are not very different from those why the genome of a human tumor cell changes so much. “What happens in a cockle is almost certainly transferred to the human genome,” he believes.
José Tubío tells an anecdote from his childhood. When he was about five years old, he went with his father to illegally collect cockles in the Noia estuary in A Coruña. “We took two huge bags with us. When we left the beach, the Civil Guard was waiting for us,” he remembers. The bitter memory of having done something wrong remained with the Tubío boy. Almost four decades later, he received 1.5 million euros from the European Research Council to finance his studies. His team has described the cockle’s reference genome and shed light on its infectious tumors, which will also help prevent mass extinctions of this species. “Who would have thought that 40 years later I would still be able to pay for this act of vandalism,” he cheers.
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