Big animals have higher cancer risk – but also evolved better defences

A comparison of 263 species supports the idea that large animals have higher rates of cancer than smaller ones. But the increase is less than expected, suggesting they have evolved ways to lower their risk

By Carissa Wong

24 February 2025

African elephants have extra copies of genes that help resist cancer

Neil Aldridge/Nature Picture Library/Alamy

Bigger animals live longer and have more cells that could go awry, so we would expect them to have a greater risk of developing cancer. A comprehensive analysis of 263 species suggests this is indeed the case, but also finds that some large animals have evolved ways to curb the risk.

“We provide the first empirical evidence to show that there’s an association between body size and cancer prevalence, meaning that bigger species get more cancer than smaller species,” says George Butler at University College London.

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The results stand in contrast to prior studies that have found no link between body mass and cancer rates. But many of these involved just a few dozen species, says Butler.

To gain a broader view, Butler and his colleagues analysed data on the size and cancer rates of 79 species of bird, 90 mammals, 63 reptiles and 31 amphibians. This data came from previous work by other researchers, who had sifted through autopsy records that logged whether captive animals – kept in places like zoos and aquariums – had cancer when they died.

The team found that larger animals were slightly more likely to have cancer at the time of their death compared with smaller ones. Across birds and mammals, every 1 per cent increase in body mass was linked to a 0.1 per cent increase in cancer rate, on average. Body mass data wasn’t available for reptiles and amphibians, so the team used body length, finding that every 1 per cent increase was linked to an average rise in cancer rate of 0.003 per cent.