In a lab in Rochester, New York, a group of were trying to grow cells taken from a naked mole rat. Instead, they ended up with a petri dish full of goo. The cells had secreted a thick, viscous substance, unlike anything typically seen in standard lab cultures. The scientists discovered that the goo contained hyaluronan, a molecule that helps keep the mole rat鈥檚 skin elastic as it navigates its cramped underground tunnels. But it may also do something far more remarkable: prevent tumours from forming.
For decades, scientists have relied on laboratory mice to unravel the complexities of cancer. These animals have helped identify cancer-causing genes, test new therapies, and build much of what we know about how tumours grow. But outside the lab, cancer exists in every corner of the natural world 鈥� and it doesn鈥檛 always play by the same rules.
Cancer development is a long, complex process that begins at the level of an individual cell. Over time, genetic material within a cell can become damaged. This damage can occur from natural processes, such as during cell division, or it can be induced by external factors including cigarette smoke and exposure to ultraviolet light. Our body has excellent defense mechanisms to detect and eliminate damaged cells. However, if this process fails, the damaged cell can divide uncontrollably resulting in a tumour. The link between cell abundance and cancer risk seems straightforward 鈥� more cells mean there is a higher chance for things to go wrong. However, this notion is countered by the unexpectedly low cancer rates in some of the largest animals on Earth, such as whales and elephants.
This phenomenon was first observed by English statistician and epidemiologist Richard Peto in 1977, who coined the term 鈥溾�� to describe the lack of correlation between body size and cancer risk. Since then, scientists have discovered that these large, long-lived animals have evolved genetic mechanisms that protect them from cancer. Humans have one copy of the TP53 gene, which is instrumental in detecting and responding to genetic damage that can lead to cancer. By analyzing the genome of 61 animals of various sizes, discovered that the African elephant boasts 20 copies of this gene, providing them with extra genetic defense mechanisms. It鈥檚 an example of natural selection at work: those with better cellular defense mechanisms are more likely to survive and pass them on.
It's well established that aging is the single greatest risk factor for cancer in humans. Yet turtles 鈥� creatures that can live well over a century 鈥� exhibit some of the lowest cancer rates in the animal kingdom. The precise mechanisms behind their resistance are still being uncovered, but have pointed to a combination of enhanced DNA repair, slow metabolism, and lower rates of cellular aging. In defying the typical link between longevity and disease, turtles can offer a quiet but compelling model for how nature has evolved ways to suppress cancer.
Cancer can spread from one site in the body to another site through a process called metastasis. In nature, the notion of cancer spreading has been observed in a way that has never been observed in people. For example, the has nearly been driven to extinction due to infectious cancers which are spread between the carnivorous marsupials by biting. In the coastal waters of New York, Maine, and Prince Edward Island, a type of leukemia has led to widespread population decline among since the 1970s. When scientists analyzed the genetic makeup of cancer cells from soft-shell clams, they discovered that all the cancer cells were nearly genetically identical to one another, even in clams from widespread regions. This also led to the discovery that the cancer from a given clam did not originate from a normal, healthy cell gone awry within that specific host 鈥� a fundamental of cancer biology. Instead, scientists believe that this type of cancer is transmissible via cancer cells floating in the water and entering other mollusks. These abnormal instances of cancer progression in the wild challenge the traditional understanding of tumour development and transmission, a crucial reminder of the complexity of the disease between - and within 鈥� species.
While genetics set the stage, environmental and lifestyle factors often determine whether cancer develops. In humans, behaviours like smoking, obesity, and UV exposure account for up to . Animals are not immune to these pressures. In a involving more than 110 000 animals from 191 species in zoos around the world, the highest rates of cancer mortality were observed in carnivores 鈥� particularly the bat-eared fox, clouded leopard, and the red wolf. While this is reminiscent of the association between and cancer risk in humans, the physiological link between diet and cancer likely differs between humans and wildlife due to additional environmental differences, including food preparation and processing, as well as evolutionary adaptations.
Captivity itself may be a risk factor. Across many species, animals in zoos experience higher cancer rates than their wild counterparts. Longer lifespans, reduced physical activity, chronic stress and diet may all contribute. These findings raise uncomfortable questions 鈥� not only about animal welfare, but also about how modern environments might shape disease in all animals, including humans.
Over years of environmental pressures and evolutionary adaptations, many wildlife species have developed impressive cancer evasion mechanisms, captivating geneticists, immunologists, and evolutionary biologists alike. However, these cancer suppression mechanisms are no match for their biggest threat of all 鈥� human activity. Chemical pollution, habitat loss, depletion of resources, and urbanization 鈥� with effects exacerbated by climate change - are profound detriments to animal welfare. The Great Barrier Reef is located under the largest hole in the ozone layer, where excess UV radiation has resulted in melanoma skin cancer in . Studying how wildlife respond to these ecological stressors may provide novel insights on cancer evolution. More importantly, continued research and exploration can deepen our understanding of cancer鈥檚 complexities while protecting the diversity of wildlife.
Lysanne Desharnais holds a PhD in Human Genetics from 黑料不打烊 University. Her interests include tumor biology, evolutionary medicine, and scientific oddities.
