Did you know elephants rarely get cancer? Here’s why

It has long been a scientific mystery: Why do elephants, who have more cells than humans, get significantly less cancer than we do? Well, thanks to a research team from the Huntsman Cancer Institute (HCI) at the University of Utah, Arizona State University, and the Ringling Bros. Center for Elephant Conservation, we may now know why.

According to the study, which is published in the Journal of the American Medical Association, elephants’ DNA contains at least 40 modified copies (known as alleles) of the same tumor-suppressing gene, p53. Us humans only have two copies of this gene. Moreover, elephants seem to have a more powerful mechanism for destroying cells that may become cancerous, as compared to humans.

“Nature has already figured out how to prevent cancer. It’s up to us to learn how different animals tackle the problem so we can adapt those strategies to prevent cancer in people,” co-senior author Joshua Schiffman, M.D., pediatric oncologist at Huntsman Cancer Institute, University of Utah School of Medicine, and Primary Children’s Hospital, said in a statement.

Elephants’ risk of cancer should be 100 times higher than ours

These natural cancer-fighters are very good for elephants, as they have 100 times more cells than humans—meaning their risk of cancer should also be 100 times higher than in humans, according to Schiffman.

However, an analysis of a database documenting 664 elephant deaths has found that elephants, in the course of their 50 to 70 years, have a cancer mortality rate of less than 5 percent; the mortality rate for humans ranges between 11 and 25 percent.

To figure out this difference, the researchers dug through the elephant genome and discovered the extra copies of the p53 gene—which code for a protein that inhibits cancers. An analysis of elephant DNA determined that these extra copies are actually retrogenes, meaning they’re modified duplicates created from RNA “copies” of DNA. These p53 retrogenes weren’t all created at once, but rather accumulated over time.

Knowing the elephants had extra copies of p53 wasn’t enough, though, to show this was the mechanism through which they avoided cancer. And so the scientists extracted white blood cells from the pachyderms and exposed them to ionizing radiation and doxorubicin, or the two agents which cause damage to DNA. DNA damage often triggers cancer, an in response to this damage, the cells destroyed themselves—a characteristic response of p53.

“It’s as if the elephants said, ‘It’s so important that we don’t get cancer, we’re going to kill this cell and start over fresh,'” said Schiffman. “If you kill the damaged cell, it’s gone, and it can’t turn into cancer. This may be more effective of an approach to cancer prevention than trying to stop a mutated cell from dividing and not being able to completely repair itself.”

In one final test, the team extracted cells from 8 elephants, 10 healthy humans, and 10 humans with Li-Fraumeni Syndrome, a syndrome in which individuals only have one copy of p53 as compared to the normal level of two, and have a lifetime cancer risk of 90%.

All cells were then exposed to radiation. The cells of those with Li-Fraumeni Syndrome self-destructed around 2.7% of the time, while healthy humans were about twice as self-destructive (7.2%), and elephants were five times more destructive (14.6%). Once again, it appears that p53 offers additional protection against cancer for the elephants.

“By all logical reasoning, elephants should be developing a tremendous amount of cancer, and in fact, should be extinct by now due to such a high risk for cancer,” says Schiffman. “We think that making more p53 is nature’s way of keeping this species alive.”

—–

Feature Image: Thinkstock