[LUM#9] Humans: A Carcinogenic Species
Human activities could lead to an increase in cancer rates among wildlife. This is a phenomenon that is greatly underestimated, and researchers hope to study it more closely to better understand the disease and perhaps develop new treatments.
Whether they live in the sea or on land, in cities or in fields, and whether they have feathers or fur, no species seems immune to cancer. The disease is also on the rise among animals, as suggested by a study conducted by researchers at the Center for Ecological and Evolutionary Cancer Research (CREEC). The researchers believe that human activities could lead to an increase in cancer rates among wildlife.
“It is now well established that global changes increase the incidence of cancer in humans, so we hypothesized that these same changes would also increase cancer rates in animals, which share the same environment as we do,” explains Mathieu Giraudeau, a researcher at the Mivegec laboratory and a member of CREEC. Global changes? Chemical pollution, of course. But that’s not all…
Chemical pollution
Pesticides, endocrine disruptors, microplastics, and pharmaceutical residues—all substances known for their carcinogenic effects, to which animals are exposed just as much as humans. “ And even more so,” laments Mathieu Giraudeau, “because while there are standards limiting exposure for humans, wild animals inhabiting agricultural areas are certainly exposed to much higher doses than we are.”
And the belugas of the St. Lawrence Estuary in Canada are a good example: in waters heavily polluted by effluents from the aluminum industry, 27% of the marine mammals examined were found to have cancer. Similarly, California sea lions show increased cancer rates caused by water pollution from organochlorine compounds.
This pollution does not spare feathered species: “It is predicted that by 2050, 99% of seabird species will have ingested microplastics.” This contamination is problematic because these microplastics release a multitude of chemical compounds into the body, some of which, such as bisphenol A, have a proven carcinogenic effect.
Light pollution
In addition to this chemical pollution, wild animals face another type of environmental change: light pollution. In humans, studies show that exposure to artificial light at night disrupts the production of melatonin, the hormone that regulates the biological clock. This disruption is associated with a higher risk of cancer. “Birds exposed to nighttime light pollution also experience disruptions in their circadian rhythm and melatonin production. We are even now seeing species where some pairs nest on streetlights in cities, ” explains Mathieu Giraudeau.
Dietary changes
Researchers have identified a third factor that may increase the incidence of cancer in animals: diet. “This is a particularly significant issue in urban areas, whether it involves food distributed to them in parks or wild animals foraging in trash cans. This diet does not meet their nutritional needs and leads to micronutrient deficiencies and changes in the microbiome that may be linked to cancer, ” explains the researcher. And urban animals aren’t the only ones affected: for example, a study showed that 92% of griffon vultures had residues of fluoroquinolones, a family of antibiotics administered to livestock whose carcasses are consumed by scavengers and which possess carcinogenic properties.
Genetic erosion
The decline of many species could also make them more vulnerable to cancer. “As the number of individuals in wildlife populations decreases, genetic diversity also declines, which can promote the accumulation of mutations that increase the risk of cancer, ” the researchers explain. This phenomenon has, in fact, been observed in two endangered species: the gray foxes of Santa Catalina Island in California and the Cape mountain zebras in South Africa, in which the decline in genetic diversity has led to increased cancer rates.
New therapeutic strategies
Despite a lack of data that researchers lament, they are unequivocal: all the animal species studied are affected by cancer. “This phenomenon remains largely understudied; we know the prevalence of cancer for only 31 vertebrate species, ” notes the researcher, who believes that cancer is greatly underestimated in wildlife. “We now need, on the one hand, to collect more data in the field to better assess cancer in wild populations and, on the other hand, to experimentally verify the impact of human activities on animals, ” explains Mathieu Giraudeau.
This field of research is of particular interest to scientists because it opens up new avenues in the fight against cancer in humans. “Some animal species develop adaptations to survive in polluted environments, while others are more resistant to cancer. If we can better understand these phenomena, we may be able to develop new therapeutic strategies to combat this disease by drawing inspiration from the anti-cancer defenses developed by these species.”
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