They are the largest land animals in the world, weighing up to 14,000 pounds and standing up to 4 meters tall. Given their size, elephants should be highly susceptible to cancer – they have at least 100 times more cells than humans – but they rarely develop the disease. In a new study, researchers shed light on the mechanisms behind elephants’ resistance to cancer – information that could fuel knowledge on cancer resistance in humans.
Theoretically, an animal’s cancer risk should increase with their size and lifespan; the bigger an animal is, the more cells they have, which should increase the rate of cell division and susceptibility to gene mutations.
In 1975, however, a study by Dr. Richard Peto, of the University of Oxford in the UK, challenged this notion. He observed that cancer incidence across species is not dependent on an animal’s size or lifespan – a theory that is now hailed “Peto’s Paradox”
Previous research has suggested that specific molecular mechanisms in elephants protect them against cancer, though Dr. Schiffman and colleagues note that such mechanisms are poorly understood.
The researchers assessed information on disease and cause of death for 36 mammalian species, including African or Asian elephants. Overall, the researchers found that cancer mortality rates did not increase with the size or lifespan of a mammal. For example, the cancer mortality rate for elephants was only 4.8%, compared with an 11-25% cancer mortality rate in humans.
He points out, however, that modern humans are particularly vulnerable to cancer, which is more down to lifestyle factors – such as smoking – that are not seen in other animals. “These behaviors are relatively recently acquired by humans, over a few hundred years, and the risks they impart far exceed prior and otherwise effective cancer suppressor mechanisms that were inherited from primate ancestors,” explains Greaves.
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