What is "Peto's Paradox"?

The lack of correlation between body size and cancer risk is known as "Peto’s Paradox".

Humans and other small-to-medium-sized mammals get cancer with high frequency, while larger mammals, like whales, do not. If cancer is essentially a negative outcome lottery at the cell level, and larger organisms have more cells, more potentially cancerous cell divisions, one would expect them to be more predisposed to cancer.

Cancer is a consequence of multicellularity and an example of multi-level selection. Because cancer develops through the accumulation of mutations, each proliferating cell is at risk of malignant transformation, assuming all proliferating cells have similar probabilities of mutation. Therefore, if an organism has more cells and longer lifespan, the probability of getting cancer should increase. Similarly, if an organism has an extended lifespan, its cells have more time to accumulate mutations.

Yet there appears to be no correlation between body size, longevity and cancer across species.

The question of "Peto’s Paradox" is how has natural selection changed the biology of large, long-lived organisms to achieve this scaling.

The general explanation for this is that large, long-lived animals are more resistant to carcinogenesis than small, short-lived animals. How they accomplish this resistance has yet to be established. Understanding this resistance could lead to new methods of cancer prevention in humans.