Are you more likely to be diagnosed with cancer if you are plus-sized? Answer is not so simple, reveals new study

A research collaboration among experts from the University of Reading, University College London, and Johns Hopkins University School of Medicine examined cancer prevalence across 263 different species spanning mammals, birds, reptiles, and amphibians. Their results challenge Peto’s paradox—a hypothesis first introduced in 1977, which proposed that an organism’s size had no significant influence on its likelihood of developing cancer.

Published on February 24 in the journal Proceedings of the National Academy of Sciences (PNAS), the study demonstrated a clear pattern: larger species generally show greater rates of tumour occurrence. However, species that evolved to grow rapidly to substantial sizes, such as elephants, simultaneously developed powerful biological mechanisms to counteract cancer.

This study incorporated an extensive dataset, the largest of its kind, by utilizing veterinary autopsy reports covering a wide range of animals—31 amphibians, 79 birds, 90 mammals, and 63 reptiles. Regardless of their differing growth patterns—some species continuing to grow throughout their lifespan while others stop upon reaching maturity—the researchers observed a consistent trend: bigger animals experienced a higher prevalence of cancer. Nonetheless, some large species, particularly elephants, evolved unique tumour-suppressing adaptations, which help them maintain cancer rates comparable to much smaller species, such as tigers.

Dr. Joanna Baker, a co-author of the study from the University of Reading, elaborated on