Elephants, with many times more cells in their bodies than humans, should be more prone to getting cancer, but the opposite is true. It's a discovery that could lead to new ways to protect people from the disease, researchers say.
Cancer is much less commonly seen among elephants than in humans, something that has puzzled scientists for many decades, but new genetic studies may have provided the answer to why that is, the researchers say.
Elephants' cells have 40 copies of a modified gene called p53, well-known as a tumor suppressor, while humans possess only two in each cell, one from each parent.
The modified genes, also known as alleles, can help damaged cells to either repair themselves or self-destruct when exposed to carcinogenic substances, the researchers explain in a study appearing in the Journal of the American Medical Association.
Although the findings cannot confirm it's the extra genes alone that make elephants resistant to cancer, if that can be proved it opens the way for possible drugs for humans that could mimic the effect, they suggest.
"Nature has already figured out how to prevent cancer," says co-senior author Joshua Schiffman, M.D., of the Huntsman Cancer Institute at the University of Utah. "It's up to us to learn how different animals tackle the problem so we can adapt those strategies to prevent cancer in people."
Why elephants resist cancer has long been a conundrum to scientists; with 100 times the number of cells that humans have, they should then be 100 times as likely to develop cancer at some point in their long, human-like life spans of 50 years to 70 years.
Yet previous studies have revealed elephants have a cancer mortality rate that's below 5 percent, compared with 11 to 25 percent in humans.
The researchers collected white blood cells taken from elephants during routine health checks, then subjected those cells to treatments to damage their DNA, which can trigger cancer.
The cells responded to the DNA damage with a common response seen when p53 is involved; they committed suicide, the researchers found.
"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,'" says Schiffman.
The impaired cell, if killed off, cannot turn into a cancerous cell, he explains.
"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," he says.
"We think that making more p53 is nature's way of keeping this species alive."