Just 4.8 percent of elephant deaths are caused by cancer. New research may explain why that rate is so low. (Tony Karumba/AFP via Getty Image)

You’ve heard that elephants never forget, but did you know they almost never get cancer, either?

It turns out that just 4.8 percent of known elephant deaths are related to cancer. For humans, cancer-related deaths are much more common — between 11 and 25 percent, scientists say.

The elephant’s low cancer rate is particularly interesting because, all things being equal, elephants should get more cancer than we do. Elephants have about 100 times as many cells as humans, and they have a lengthy life span, about 70 years. That gives a lot of cells a lot of opportunity to mutate and turn malignant.

For decades scientists have wondered why elephants and large mammals in general are not more prone to cancer than smaller mammals are. The question even has a name — Peto’s paradox. But new research may shed light on pachyderms’ cancer-fighting abilities.

‘Guardian of the genome’

In a paper published last week in the Journal of the American Medical Association, a team of scientists shows that African elephants have 20 copies (and therefore 40 alleles) of a gene called TP53, sometimes called the “guardian of the genome” for its ability to create a protein that suppresses tumors. Humans have just one copy (two alleles) of this gene.

An elephant splashes at sunset in the waters of the Chobe river in Botswana Chobe National Park. (Chris Jek/AFP via Getty Images)

Over the course of three years, the research team, led by pediatric oncologist Joshua Schiffman of the Huntsman Cancer Institute in Salt Lake City, performed experiments that show how these extra copies of TP53 help elephants fend off cancer.

Sequencing of elephant DNA showed that while African elephants have 20 copies of TP53, 19 of them are retrogenes, meaning they got inserted into the elephant genome at a later date than the original gene.

This suggests that these additional genes were preferentially selected over the course of elephant evolution, and probably helped elephants in some way.

To see if they did, indeed, help elephants fight cancer, the researchers collected white blood cells from elephants and humans. Then they exposed those cells to radiation that caused the double strands of DNA to break.

Surprising results

The researchers expected that the elephant cells with all those extra TP53 genes would repair themselves faster than the human cells, but that’s not what they observed.

Instead, they saw that the elephant cells were dying at a much higher rate than the human cells. While this may sound like a bad thing, it isn’t. Part of TP53’s suppression strategy is to cause a damaged cell to commit suicide rather than pass on potentially harmful mutations.

“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,’ ” Schiffman said in a statement. “If you kill the damaged cell, it’s gone, and it can’t turn into cancer. This may be more effective . . . an approach to cancer prevention than trying to stop a mutated cell from dividing and not being able to completely repair itself.”

Schiffman said that his team’s next step is to see if it can use what it learned from elephants to help people with cancer.

— Los Angeles Times