Cancer impacts other animals just as it does humans. New research, though, shows how animal size, and how quickly a species evolved to be their current size, impact their likelihood of getting cancer. The findings may help understand cancer defenses in animals and improve treatment in humans.

Johns Hopkins University School of Medicine, University College London, and the University of Reading recently teamed up to investigate cancer prevalence across 263 species, including mammals, birds, reptiles, and amphibians. By looking at veterinary records of autopsies on these animals, the team wanted to see if larger, longer-living animals had higher rates of cancer, which may be expected due to the number of cell divisions they experience in their lifetimes. 

The findings, published in Proceedings of the National Academy of Sciences, showed that larger, longer-lived animals do in fact have higher rates of both benign and malignant tumors. Even though birds and mammals stop growing at some point, while amphibians and reptiles can keep growing, this was true for all four types of animals. 

Chris Venditti, senior author and professor at the University of Reading, says, "Everyone knows the myth that elephants are afraid of mice, but when it comes to cancer risk, mice are the ones who have less to fear. We've shown that larger species like elephants do face higher cancer rates - exactly what you'd expect given they have so many more cells that could go wrong.” 

However, this is not the only information their research uncovered. They also found that mammal and bird species that evolved larger body sizes more rapidly, like elephants, had lower rates than would be expected given their size. This suggests that this rapid size evolution came with the ability to better control cell growth and thus the development of anti-cancer defenses.

While this was true in broad terms, there were species with a more pronounced impact. For example, rapid body size evolution was linked with a 56% reduction in predicted cancer rates for the Asian elephant but only 12% for the long-haired fruit bat.

Further, there were also differences in expected rates and observed rates. The budgie had both the highest rate of cancer and the largest underestimation based on size, while the naked mole rat had very low rates and the largest overestimation.

The study authors write, “These results highlight subsets of species that, despite their body size and historic rate of body size evolution, have an exceptionally high or low prevalence of malignancy and thus serve as a target group for future mechanistic studies of malignancy defense.”

They say that understanding these defenses may help shine light on how cancer grows and could help with treatment in humans. You can read more here.