For mammals, eating other animals may increase cancer risk

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Enlarge / These rodents apparently manage to avoid developing cancer.

Cancer is a sad fact of life, as nearly 40% of people are diagnosed with it at some point in their life. But humans are not alone in this case. Many different species can also develop the disease, some more often than others. By studying these species and their habits and natural defenses (or lack thereof), we can learn new ways to fight disease.

New research that involves a full cancer investigation shows that many mammals can actually get cancer. To better understand this, the team looked at the records of 110,148 animals of 191 species that died in zoos. The data comes from Species360, an international non-profit organization that collects and unifies this kind of data from zoos around the world, according to Orsolya Vincze, a researcher at the Center for Ecological Research in Hungary and one of the authors of the article.

Using data collected by the organization, the research team was able to “collect information on the causes of animal deaths,” she told Ars.

The team limited their search to data points taken after 2010 because prior to that record keeping was not as good, she said. Additionally, the team only studied animals in zoos because it is difficult to collect this type of information about species in the wild. Animals in their natural habitats that contract cancer are also more likely to prey or starve – they tend to die sooner, Vincze said.

“You have to go to zoos where every individual is tracked and you know when they die and you know what they died of,” she said.

Lessons learned

Most of the species the team studied were at risk of cancer. The only two exceptions, as far as data goes, were the blackbuck (a kind of antelope) and the Patagonian mara (a kind of rodent). The data included information on 196 and 213 individuals of these species, respectively.

Carnivores, however, were particularly prone to cancer. In the data set, more than a quarter of cloudy leopards, bat-eared foxes and red wolves died from cancer, for example. According to Vincze, there are certain hypotheses as to why this could be the case.

On the one hand, carnivores have different microbiomes compared to other types of animals, which could be a problem because a rich community of microorganisms can help limit cancer. Carnivores, especially those in captivity, also have limited ranges. A lack of physical activity could also contribute. Raw meat, like that eaten by most carnivorous mammals, can also contain bacteria or other microbes that can increase the risk of cancer. For example, raw cow meat can carry the bovine leukemia virus, which some studies have shown may increase the risk of breast cancer in humans. Overall, however, Vincze said more research needs to be done in this area.

The bigger they are

Surprisingly enough, animal size does not correlate with cancer risk. Cancer mutations usually occur when cells divide. In theory, a large animal living longer should have more cell divisions than smaller animals and, therefore, they should be more prone to cancer. It’s seen in dogs and humans – the larger members of both species tend to have a higher cancer risk, Vincze said.

However, larger species are not particularly at risk of contracting the disease, a phenomenon called the Peto Paradox. According to Vincze, this is probably due to the fact that these species developed means to fight cancer in their genetic past. By studying the mechanisms by which these large species suppress cancer, we could potentially develop ways to fight the disease. And, by studying why some species have higher cases of the disease, we can learn more about it in general, Vincze said.

“We could really look at molecular mechanisms and identify them, and try to come up with new methods of treating cancer in humans and animals,” she said.

Nature, 2021. DOI: 10.1038 / s41586-021-04224-5 (About DOIs)


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