Lumbering elephants have so many cells but get few cancers, says a doctor who investigated rates of the disease in different mammals.
Compared with other mammals, elephants seem to have a lower-than-expected rate of cancer, researchers say in Thursday's issue of JAMA.
To reach that conclusion, Dr. Joshua Schiffman, a pediatric oncologist at the University of Utah School of Medicine in Salt Lake City and his co-authors surveyed information on the disease and the cause of death for 36 mammalian species.
They also compared responses to DNA damage in elephants with healthy human controls and people with Li-Fraumeni, a genetic syndrome that predisposes them to more than a 90 per cent lifetime risk of cancer and early childhood cancers.
More than 35 years ago, epidemiologist Richard Peto of Oxford University observed the incidence of cancer doesn't seem to be related to the number of cells in an organism. Peto's Paradox says larger and longer-living mammals develop cancer less frequently than expected
"To our knowledge, this study offers the first supporting evidence based on empirical data that larger animals with longer life spans may develop less cancer, especially elephants," Schiffman and his team wrote.
"The cancer mortality rate for elephants was found to be less than five per cent compared with a cancer mortality rate for humans of 11 per cent to 25 per cent."
The researchers also found elephants had multiple copies of a key tumour suppressor gene called TP53 that has mutated in many human cancers. African elephants have at least 20 copies, while people with Li-Fraumeni syndrome inherit only one version instead of the usual two for humans.
The lower-than-expected cancer rate in elephants may be related to their multiple copies of TP53, "the guardian of the genome," the investigators proposed.
The gene's " job is to fly around our cells and make sure if any mutations or changes develop in the DNA that cell is stopped and repaired or maybe even killed so it can't go on and propagate those changes," Schiffman said in a university video.
"It was if the elephants had said it is so important that we don't get cancer why even try to stop the cell and repair it when we can just kill it and start over again? That seems to be the safest way to make sure that mutations that can cause cancer won't be passed on."
But a journal commentary published with the study suggests it isn't clear what lessons the study of elephants holds for understanding human cancer risk.
"Perhaps the main message from this innovative investigation is to bring into focus the question of why humans appear to be so ill-adapted to cancer, given the average size and lifespan," wrote Mel Greaves of the Institute of Cancer Research, London, U.K.
Focus on lifestyle to prevent cancer
To Greaves, the lesson is to focus on the causes of cancer.
"If you're looking at prevention of cancer, which I think has huge promise, then we need to focus on lifestyle," Greaves said in an interview.
If you look at human metabolism on a scale compared with other animals, we're out of synch for our size, he said.
"Our metabolic rates are too high, too fast for our size," Greaves said. "And that comes from the fact we eat too much and use too little energy."
The Utah researchers are patenting the elephant TP53 gene in the hopes of using it in humans.
The research was supported by Huntsman Cancer Institute, the U.S. National Cancer Institute, Huntsman Cancer Foundation, Intermountain Healthcare Foundation, Primary Children's Hospital Foundation, Soccer For Hope, Utah's Hogle Zoo, Ringling Bros. and Barnum & Bailey Circus, U.S. Department of Energy, and the U.S. Department of Defence.