In our vulnerability to cancer, we humans are not alone.
In fact, every creature that roams our planet can fall victim to this disease caused by uncontrolled cell growth; just some are more predisposed to it than others.
Key to controlling cancer, in humans and in other animals, is gaining a full understanding of it. And that’s why researchers from Arizona State University and UC Santa Barbara have undertaken a decade-long study of cancer across almost 300 different animal species.
Their research, which led them to examine over 16,000 necropsy reports and was recently published in the academic journal Cancer Discovery, has aided scientific understanding of cancer’s prevalence across the animal kingdom. In doing so, it has also challenged Peto’s Paradox, changing everything we thought we knew about cancer across species.
This evolutionary concept purported that the longer the lifespan, the larger the animal, and thus the greater number of cells, the more chance a species had of developing cancer.
However, the researchers’ work suggests that there is only a very small increase in cancer rate with the body size and cell count of an animal.
Fundamentally, the research proves, Peto’s Paradox was flawed because we didn’t have much understanding of cancer in the animal kingdom, as Arizona State’s Carlo Maley – author of the study – explained in a statement:
“Until recently, we didn’t know cancer rates in any species beyond humans, dogs and naked mole rats. I’m excited to discover all kinds of different species with extremely low cancer rates. They can show us how nature has solved the problem of preventing cancer.”
However, Peto’s Paradox is exactly that – a paradox. So while it suggests that bigger animals have greater instances of cancer, it also suggests that they are better poised to prevent it too, as Amy Boddy – co-author of the study and a biologist from UC Santa Barbara, explains in another statement:
“Bigger, long-lived species invest more in somatic maintenance. I’d expect them to be better at defending against cancer, because they have to, in order to grow big and live long. It’s not really a paradox from an evolutionary point of view.”
To undertake their study, the scientists used data from 99 animal care facilities, including zoos and aquariums. The necropsy reports, compiled upon the death of an animal by a vet, set forth any malignant or benign tumors that the animal may have had.
This helped the researchers to understand how – in captivity at least – cancer rates occur in different species.
And the research was clear: while some animals had an unusually high incidence of tumors – including ferrets, opossums and hedgehogs, who had a 63% chance of tumors – cancer was present across all species, as Boddy continues:
“One thing that became really clear once we started gathering the data is that everything gets cancer. It’s just something about being a multicellular organism. No one’s completely protected.”
But why do some species develop tumors more frequently than others? Well the research suggests that some animals are more likely to have developed, through evolutionary processes, more cancer-suppressing genes than others.
This explains why some of the largest animals, including whales and elephants, had a much smaller rate of tumors.
Boddy explained, in the statement, that elephants were known for having developed, over time, a gene that reduced their risk of cancer – contributing to their long life spans.
This is a direct contrast to the ferret, whose body and life are much smaller:
“Cancer is quite evolutionarily old, and is a constant selective pressure. As animals developed into distinct species, they’ve had to undergo different genetic trade-offs and employ different strategies. One well known strategy is that of elephants, who have 20 copies of P53, a tumor suppressor gene. Other strategies may involve lower somatic mutation rates, so these mutations are slower to accumulate and develop into cancer.”
While this is notably an animal-related study, the research only furthers our understanding of cancer. Our understanding of cancer in the animal kingdom can potentially help us to help animals in the years to come.
It can also aid in our understanding of human cancer, and how specific genes may offer protection.
When it comes to cancer, all information is valuable.
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