Natural Defenses Against Cancer

We now know that cancer is a disease of a loss of control over cell division. A commonly-held belief is that larger animals such as humans (with more cells and hence more cell divisions) and animals that live a long time (with more opportunity for cell damage to occur over time) should be more prone to cancer than smaller, short-lived animals.

A recent study shows that the size-and-time belief is incorrect. In a study of 36 mammalian species, the authors found no evidence of increased incidence of cancer in larger or longer-lived animals. Elephants live much longer than humans and have many more cells, but fewer than 5% die of cancer, compared to a cancer death rate of 11-25% in humans. And a particular strain of rat called the naked mole rat lives up to 30 years - much longer than other rats - without being prone to cancer. So the question becomes, why is that?

It turns out that nature has developed defenses against cancer. During evolution, elephants developed extra copies of a cancer-fighting gene called p53. (Humans have one copy; elephants have more than 20.) The p53 gene causes damaged cells to commit suicide, effectively preventing them from becoming cancerous. The naked mole rat developed a protein that blocks the growth of fast-dividing (potentially cancerous) cells.

Researching the natural defenses against cancer in other long-lived or large animals might help us better understand how cancer develops in humans and how best to fight it.