Cancer is a disease in which abnormal cells divide uncontrollably. Most cancers start due to gene mutations which accumulate over the course of an animal’s life. Each time a cell divides, there is chance that the genes within the cell will mutate. If genes which control the normal growth, division, and death of cells become mutated, the cell can become cancerous. Theoretically, the longer an animal lives and the more cells within its body, the higher the chances are that enough mutations will accumulate for cancer to develop — but not always.

Whales, dolphins, and porpoises belong to a group collectively known as cetaceans, containing some of the largest and longest-lived species of mammals on Earth. Yet, cetaceans have some of the lowest cancer rates. This lack of cancer suggests cetaceans must have evolved effective cancer suppression mechanisms which humans and other mammals lack. 

Researchers trying to better understand how cetaceans suppress cancer studied the evolution of over 1000 tumor suppressor genes, or TSGs in 15 mammalian species, including cetaceans. TSGs are known to affect cell division, repair mistakes in DNA, and control when cells die — important processes for keeping cancer at bay. Published in Proceedings of the Royal Society B, their results show that over time cetacean species including orcas and bowhead whales had positively selected TSGs that are linked to a variety of cancers. The team also found that cetacean species gained and lost genes at a rate more than double that of other mammalian species, which may have accelerated evolution of TSGs in cetaceans. 

These findings point to the evolutionary mechanisms that allowed large, long-lived species to overcome the threat of cancer. By studying the genes implicated in cancer suppression and understanding how they might do so, researchers may gain useful insights into how to suppress cancer in humans.