Researchers Studying Cancer in Wildlife Grapple With Why Some Get the Disease While Others Don’t
“Studying wildlife cancer, and more generally the evolution of cancer across the tree of life, is extremely promising to develop innovative therapies to treat cancer in humans,” Mathieu Giraudeau, a researcher at France’s La Rochelle University who has been focusing on cancer in wild animals since 2018, told VOA.
“The idea behind this is that some species have evolved some mechanisms to limit cancer initiation and progression,” he said. “If we identify and understand these mechanisms, then the goal is to use them as a source of inspiration to develop new therapies.”
Cancer affects both humans and animals but its impact on wild animals has been difficult to uncover.
“There are no basic blood tests to detect cancer in the wild animals,” Giraudeau told VOA, “so most of the studies have to use necropsies [post-mortem examinations of animals] to detect cancer cases in wild animals. That's why using zoo animals is a fantastic opportunity, since a necropsy is performed for most of the animals dying in zoos.”
Researchers say there are more questions than answers regarding cancer in wild animals, which are hard to study in their natural habitat because they move around and are therefore difficult to observe over time.
“We don't really know much about the different kinds of animals species that get cancer or how much,” biologist Carlo Maley, director of the Arizona Cancer Evolution Center at Arizona State University, where he is studying cancer in wild animals, told VOA.
“We've been focusing on collecting data to find which species are super susceptible or super resistant to cancer,” he said, “and we’re looking at questions such as how has nature figured out how to prevent cancer and then, can we translate that to humans.
It seems large and long-lived species “have evolved some powerful mechanisms to fight against cancer, and we now need to understand these mechanisms,” Giraudeau said.
They include elephants and whales.
“Elephant cells are super sensitive to DNA damage, and even with just a little DNA damage, the cell will commit suicide and not risk getting mutations,” Maley said. “So it seems to be a strategy for avoiding cancer by killing off a potentially dangerous cell, rather than risk getting a mutation that could lead to cancer.”
In Australia, however, that has not been the case for a much smaller animal, the Tasmanian devil. The carnivorous marsupials have been nearly wiped out from cancerous tumors growing in and around their mouths.
“Devils bite each other, particularly around the face, as part of their normal behavior,” Cambridge University veterinary medicine professor Elizabeth Murchison told VOA.
Murchison, a researcher on the genetics and evolution of transmissible cancers, added, “Tasmanian Devils have a transmissible cancer that spreads between the animals by the transfer of living cancer cells. There are, in fact, two independent transmissible cancers in Tasmanian devils, which was a surprise, and both are spread during biting, and result in fatal facial tumors.”
Murchison, who grew up in Tasmania, “passionately” hopes the endangered species can be saved.
“There is currently no way to control the disease,” she said. “Research directed towards developing a vaccine is ongoing, but it will be a long road to developing an effective protective vaccine.”
Even much smaller creatures, like shellfish, are dying from cancer.
On Whidbey Island in Washington state, a massive die-off of cockles, a type of bivalve mollusk, were found on the beach. It turns out the cockles had a leukemia-like contagious cancer that affects the cells that live in their hemolymph, the equivalent of blood.
It is another transmissible cancer, found in many shellfish species worldwide, but first discovered in these cockles in 2018. The cancer cells in the sea can float to enter nearby cockles, spreading the disease.
“The whole cell of the cancer moves from one animal to the next,” unlike conventional human cancer that arises due to cell mutations that don’t move from one person to another, said Michael Metzger, assistant investigator at the Pacific Northwest Research Institute in Seattle, Washington.
Researchers are working to find the cause of the contagious cancer and using genetic analysis, to learn how the disease evolves.
It’s not clear how the cockles first got the disease.
It’s possible it could have been brought to the area by a boat carrying diseased shellfish, he said. He also said environmental stressors may have played a part, including global warming.
Scientists say there is a long way to go before cancer in wild animals is widely understood and how that may help battle human cancers in the future. Besides genetics, they are also looking at the effect of viruses, pesticides, habitat destruction and pollution.
Human cancers are short-lived, from an evolutionary perspective,” Murchison said. “Our work gives us insight into how cancers evolve over long time-periods.”
“I think the main benefit is going to be preventing cancer as opposed to curing it,” said Maley. But there's some possibility that the mechanisms that prevent cancer could also be translated into potential therapies.”