Logically, pachyderms should get cancer more often than men. With their 4800 kg of weight, African elephants have 100 times more cells than ours: the more cells (and cell divisions), the greater the likelihood of something going wrong; moreover, these mammals reach the remarkable age of 60 years.
Still, the mortality rate from cancer in elephants - as well as in other large animals, including whales - is surprisingly low. This dilemma, known as the Paradox of Peto, from the name of the English epidemiologist who described it in the 1970s, may now have found a solution.
Kissed by genetics. Two independent studies published last week show that the DNA of African elephants has 20 copies (then 40 alleles) of one of the most potent tumor suppressor genes, known as p53 (or TP53). That of the Asian elephants has 30 to 40 copies; that of human beings, only one copy (two alleles). When a cell suffers genetic damage that makes it potentially carcinogenic, p53 inhibits its division until the trouble is remedied, or encourages suicide to prevent the damage from expanding.
Nobel Prize in Chemistry for studies on DNA repair processes
suicide. To understand how the gene works in pachyderms, Joshua Schiffman, a child oncologist at the University of Utah, together with his colleague Charles Maley, of Arizona State University, subjected some African elephant cells to ionizing radiation, discovering that they had twice as many probability of dying from the reported damage compared to human cells.
The hypothesis is that the extra copies of the p53 gene allow damaged cells to go more easily to apoptosis (a sort of programmed self-destruction) thus preventing the spread of the tumor. The results are consistent with those of another study on the topic conducted by Vincent Lynch, of the University of Chicago.
Evolutionary causes. What is certain is that the strategy works. Less than 5% of the elephants, according to the data collected in the two studies, die of cancer; in humans, this percentage can reach 25%.
The next step will be to understand if and how this discovery can be useful in human cancer research. However, there may also be a natural slowing down of metabolic activity in large animals, which affects the rhythm of cell division, favorably acting on the health of pachyderms.