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The Paradox That Keeps Doctors Awake at Night

If cancer is caused by a genetic fault in a single cell, and all cells theoretically have the same chance of turning cancerous, one would expect much bigger animals, having far more cells in their body, to have proportionally higher rates of cancer. However, this is not what we observe! This is Peto’s Paradox.

Peto’s paradox is named after epidemiologist Richard Peto, who discovered this phenomenon when studying the relationship between time and cancer development in mice. Peto observed that the probability of cancer progression was related to the duration of exposure to certain cancer-causing molecules (carcinogens). As part of his work, he began to wonder why humans, who possess 10,000 times more cells and live 30 times longer than mice, have similar rates of developing cancer. Further, cancer was not a major cause of mortality for large and long-lived wild animals, despite the increased theoretical…