Cancer is a disease that arises when your body makes mistakes during cell division. Several mutations in strategic genes of your DNA can cause cells to go berserk, dividing uncontrollably and forming a tumor. Our bodies have defense systems in place to track and eliminate cancer cells, but the odds are really stacked up against us.
Every time a cell divides, there is a risk of producing a cancer-causing mutation. Therefore, organisms with more cells should be more at risk for cancer. However, this theory doesn’t happen in real life. Elephants, the largest land mammal, have over 100 times more cells than humans. Blue whales, the all-around largest mammal, have 2000 times more cells than humans! We would expect them to have much more cancer than humans do, but the puzzling fact is that their rates of cancer are much lower than us. This unsolved mystery is Peto’s Paradox.
The numbers don’t add up: animals with vastly more cells have extremely low rates of cancer, and small animals like mice can have high rates of cancer. Scientists have suggested theories about why this happens – here are two of them.
One reason elephants and blue whales seem to have very low rates of cancer is evolution. These big animals must evolve extensive “anti-cancer” defense systems to survive, or face extinction. The African savannah elephant has 20 copies of a tumor suppressor gene called TP53. This gene instructs cells to self-destruct if they become cancerous. For comparison, humans only have one copy of TP53. It would make sense for an animal with more copies of cancer-fighting genes to be more resistant to cancer.
Another factor that may contribute to large animals’ resistance to cancer is different metabolic rates. Bigger animals tend to have lower metabolic rates, which means their cells convert nutrients to energy more slowly. They also have bigger cells, which divide more slowly compared to cells of smaller animals. The conclusion from these two observations is that the lower metabolic rate and division rate of large animals lowers their chance of developing cancer, as opposed to the rapidly-dividing cells of small mice.
What may be the most interesting answer to Peto’s pardox is hypercancers. In short, hypercancers, or hypertumors, are the cancers of cancer. The theory goes that some cancer cells are so mutated that they separate from their original tumor and go rogue. The new cancer ends up competing against their original tumor for nutrients and eliminating them. This cycle can repeat indefinitely every time a new hypertumor shows up. The hypercancer theory suggests that there actually might be a ton of tumors in a blue whale, but since they’re constantly defeated by new cancers, the animal isn’t affected.
New breakthroughs in cancer research are slowly piecing together its inner mechanisms to develop ways of fighting it. I think the perspective of looking at how other animals deal with this almost universal disease will yield very insightful discoveries. Scientists have looked at nature for so many innovations and ideas, and we still have a lot to learn from our fellow organisms. In the meantime, it’s nice to look to our gentle giants for ways to conquer cancer.