Cancer prevalence is remarkably low in turtles and is correlated with life history traits in birds, mammals, and squamates

Cancer rates vary widely across vertebrate groups. Identifying species with lower-than-expected cancer prevalence can help establish new models for unraveling the biological mechanisms underlying cancer resistance. Theoretical predictions suggest that cancer prevalence should be positively associated with body mass and longevity in animals. Yet, in mammals, the best studied vertebrates in terms of cancer, this prediction does not hold true: a phenomenon known as Peto’s paradox. Despite mounting work disentangling the biological basis of Peto’s paradox, it is still relatively unknown whether other major vertebrate groups behave similarly to mammals or might hold new keys to understanding cancer biology. Here, we present the largest dataset available so far on cancer prevalence across all major groups of tetrapod vertebrates: amphibians, birds, crocodilians, mammals, squamates (lizards and snakes), and turtles. We investigated cancer prevalence within and among these groups and its relationship with body mass and lifespan. This is the first study to analyze non-avian reptile groups separately. We found remarkably low cancer prevalence in birds, crocodilians, and turtles. Counter to previous studies, we found that body mass and lifespan are inversely related to cancer prevalence in mammals, although Peto’s paradox still holds true in this group. Conversely, we rejected Peto’s paradox in birds and squamates, as neoplasia prevalence was positively associated with body mass in these groups. The exceptionally low cancer prevalence in turtles and extensive variation in cancer prevalence amongst vertebrate families hold particular promise for identifying species with novel mechanisms of cancer resistance.