Larger animals have many more cells than smaller ones. Why don't they get cancer a lot more often?

There is an idea in biology that larger animals should be much more prone to cancer since they have more cells. But it doesn’t work out that way.

Arizona State University researchers took 10 years gathering data to study cancer prevalence among hundreds of different species.

That idea that larger animals don’t get cancer as often as expected is called Peto’s Paradox and was the motivation for the study.

Previously there had been a lack of evidence to really examine that.

This paper analyzed 16,000 animal autopsies, called necropsies, of 292 species. Contrary to the paradox, it found larger animals actually did die from cancer more often than smaller animals, but only slightly.

ASU professor Carlo Maley says the length of time an animal gestates during pregnancy could lead to some answers.

“If it’s just about pregnancy you should see females getting cancer less often than the males. If it's about the development of the embryo and the fetus into a baby, then both males and females should have low cancer. So we're in the process of testing that from our data.” he said.

Maley says the findings could help lead to better cancer treatments for humans.

"If you understand the mechanism by which the animal is protecting itself from cancer, we might be able to replicate that either by changing the exposures in humans or or drugs that mimic that effect," he said.

The study was published in the journal Cancer Discovery.