[LUM#9] Humans, a carcinogenic species

[LUM Magazine] - Published on April 9, 2019 in Science-Society

Human activities could lead to an increase in cancer rates in wildlife. This is a highly underestimated phenomenon that researchers want to study more closely in order to better understand this disease and perhaps develop new treatments.

Whether marine or terrestrial, urban or rural, feathered or furry, 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 Research on Cancer (CREEC). They believe that human activities could lead to an increase in cancer rates among wildlife.

"It is now proven that global changes increase the incidence of cancer in humans, so we assumed that these same changes would also increase cancer rates in animals, which share the same environment as us," explains Mathieu Giraudeau, a researcher at the Mivegec laboratory and member of CREEC. Global changes? Chemical pollution, of course. But that's not all...

Chemical pollution

Pesticides, endocrine disruptors, microplastics, pharmaceutical industry 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 there are standards limiting exposure for humans, but wild animals living in agricultural areas are certainly exposed to much higher doses than we are."

The beluga whales of Canada's St. Lawrence Estuary are a good example: in water heavily polluted by effluents from the aluminum industry, 27% of these marine mammals examined were found to have cancer. Similarly, California sea lions are showing 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 are facing another type of environmental change: light pollution. Studies show that exposure to artificial light at night disrupts the production of melatonin, the hormone that regulates the biological clock in humans. This disruption is associated with a higher risk of cancer. "Birds exposed to nighttime light pollution also experience disruptions to their circadian rhythm and melatonin production. We are now even 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 problem in urban areas, whether it's food distributed to animals in parks or wild animals feeding from trash cans. This diet does not meet their needs and leads to micronutrient deficiencies and changes in the microbiome that may be associated with cancer, " explains the researcher . And urban animals are not the only ones affected: for example, one 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 have carcinogenic properties.

Genetic impoverishment

The decline of many species could also make them more vulnerable to cancer. "If there are fewer and fewer individuals in wild animal populations, there is also less genetic diversity, which can promote the accumulation of mutations that favor the development of cancer, " the researchers explain. This phenomenon has been verified in two endangered species: gray foxes on California's Santa Catalina Islands and Cape mountain zebras in South Africa, where declining genetic diversity has increased cancer rates.

New therapeutic strategies

Despite a lack of data lamented by researchers, they are categorical: all animal species studied are affected by cancer. "This phenomenon remains largely unstudied; we know the prevalence of cancer in only 31 vertebrate species," notes the researcher, who believes that cancer is greatly underestimated in wildlife. "We now need to collect more data in the field to better assess cancer in wild populations and experimentally verify the impact of human activities on animals, " explains Mathieu Giraudeau.

This field of research is of particular interest to scientists as 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 can consider developing new therapeutic strategies to fight this disease by drawing inspiration from the anti-cancer defenses developed by these species."

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