Peto’s paradox

Peto’s Paradox

Peto’s paradox refers to the observation that there is no clear correlation between the size or lifespan of an organism and its risk of developing cancer. The paradox is named after Richard Peto, a British epidemiologist who first described this phenomenon in the 1970s.

Research on Peto’s paradox has primarily focused on understanding why larger animals, which have a greater number of cells and a longer lifespan, do not have a correspondingly higher incidence of cancer compared to smaller animals. This paradox challenges the assumption that cancer is solely driven by mutations in cells and suggests the existence of additional mechanisms that protect against cancer development.

Several hypotheses have been proposed to explain Peto’s paradox:

1. Evolutionary Trade-Off: This hypothesis suggests that larger animals have evolved more effective tumor-suppression mechanisms to counterbalance their increased risk of cancer. It is believed that these mechanisms, such as enhanced DNA repair, more robust immune systems, and better cellular surveillance, help prevent the uncontrolled growth of abnormal cells.
2. Cellular Senescence: Cellular senescence is a process by which cells permanently stop dividing in response to various stressors, including DNA damage. Larger animals may have evolved more efficient cellular senescence mechanisms, which limit the proliferation of potentially cancerous cells.
3. Cancer Suppressor Genes: Larger animals may possess a larger number of copies or more effective versions of tumor-suppressor genes, which help regulate cell growth and prevent the development of cancer. This hypothesis suggests that the complexity and redundancy of the genetic regulatory network in larger animals contribute to their lower cancer rates.
4. Evolutionary Constraints: This hypothesis proposes that there are fundamental biological constraints that limit the size of tumors in larger animals. For example, the diffusion of oxygen and nutrients to sustain tumor growth may become limiting in larger organisms due to their increased size, reducing the likelihood of tumor progression.

Research on Peto’s paradox involves comparative studies across different species, investigating the molecular and genetic factors that contribute to cancer resistance in larger animals. By studying the mechanisms that protect against cancer in these species, scientists hope to gain insights that could be applied to developing new cancer prevention and treatment strategies for humans.

Overall, Peto’s paradox highlights the complex interplay between factors such as size, lifespan, and cancer susceptibility, challenging conventional assumptions about cancer development and providing valuable insights into the biological mechanisms underlying cancer resistance in different organisms.