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It may surprise you, but one of the most confusing mysteries of the medical world concerns the animal world, or rather the question - why do some species of animals do not get cancer while others are affected by tumors that shorten their lives?
On the one hand, whales and elephants tend to have low rates of cancer (on average only 1 in 20 elephants develop the disease compared to 1 in 5 humans), but on the other hand, it is the leading cause of death for dogs and cats.
Foxes and tigers are also susceptible to the disease, while sheep and antelopes are not.
Bats are also relatively well protected against cancer, but mice are not protected at all.
In humans, cancer is a leading cause of death killing about 10 million people a year.
According to an article published in the British Guardian, the mystery gets even more complicated if you go into the small - or large - details, since many giant creatures, including whales and elephants, do not usually get cancer, although logic says that they are at particular risk because they have a huge number of cells , each of which may stimulate growth.
"Pito's Paradox"
This is "Pito's paradox", named after the British statistician Richard Pito who described it for the first time, and is the focus of investigations by scientists from the Wellcome Sanger Institute, in Cambridge, who work with researchers from several centers, including the Zoological Society.
of London (ZSL).
An albino whale was spotted off the coast of Argentina on May 3, 2017 (Photo: Reuters)
"Cancer is a disease that occurs when a cell in the body undergoes a series of DNA mutations and begins to divide uncontrollably, and the body's defenses fail to stop this growth," Alex Kagan, head of the project, told the Guardian.
"The logic says - the more cells an animal has, the greater the risk of getting cancer."
From this point of view, there are certain species of whales that should not be able to reach the age of one year without getting cancer, because they have so many cells - several billion compared to humans, who have only trillions.
But in reality something else happens.
The average lifespan of bowhead whales (Balaena mysticetus) ranges from 100 to 200 years, for example, while elephants have an average lifespan of about 70 years.
But compared to humans, they all have thousands of times more cells, each of which is a potential starting point for a mutation that will lead to cancer.
In order to understand this paradox, Sanger's team studied a variety of animals that had died of natural causes at London Zoo.
All were mammals and included lions, tigers, giraffes, ferrets and mahouts.
Rats (Photo: ShutterStock)
An animal that lives for decades and does not get cancer
But small animals were also tested - one of them is a naked rat or a naked marten.
"They are the size of a mouse but they live about 30 years and almost never get cancer," the researchers said.
In fact, even when scientists try to make them get cancer through laboratory manipulations they rarely succeed.
The researchers isolated cells known as intestinal crypt cells from each animal that died and studied their genomes.
"These cells are constantly renewed by stem cells and are a great way to compare genomes. We used them to count the number of mutations each species accumulates each year," Kagan added.
"What we found was very striking. The number of mutations each accumulated each year varied greatly. Essentially, we found that long-lived species accumulated mutations at a slower rate while short-lived species did so at a faster rate. For example, in humans we get About 47 mutations per year, while in a mouse that lives an average of about 4 years, it is about 800 mutations per year. For comparison, the average human lifespan is 83.6 years."
In addition, it was found that at the end of the life span, all the different animals studied accumulated about 3,200 mutations.
"The similar number of late-life mutations in these different animals is striking, although it remains unclear whether this causes aging," Kagan said.
However, it is not clear exactly how long-lived animals successfully slow down their DNA mutation rate.
Additionally, the relationship between mutation rates and lifespan was only observed for animals with low to medium lifespans.
Cancer mortality in elephants is estimated at less than 5%.
Elephants (Photo: ShutterStock, Shutterstock)
The next step is to also check for reptiles and insects
In the case of elephants, a study published a year ago involving scientists from seven research institutions including the University of Oxford and the University of Edinburgh showed that despite their large body size and life expectancy similar to humans, cancer mortality in elephants is estimated to be less than 5% (and not up to 25% in humans).
Scientists link elephants' high resistance to cancer to their 20 copies of the p53 gene - the 'guardian of the genome' - compared to the single p53 gene found in other mammals.
This gene belongs to the group of tumor suppressor genes (tumor inhibitors) and is one of the most studied genes in the field of cancer worldwide.
Another study by Dr. Gerlind van de Walle, a microbiology and immunology expert at the Baker Institute at Cornell University is examining breast tissue from a variety of mammals with varying incidences of breast cancer to investigate how breast cancer begins. Her group created cell cultures using breast tissue from humans, monkeys, rodents , pets, livestock and wildlife, which they can use for laboratory experiments. They have already found that cells taken from horses and cows—animals that rarely develop breast cancer—die quickly after undergoing DNA damage. In humans and dogs, however, damaged cells The DNA continues to divide, which may eventually lead to additional tumors and their metastases.
So far the first phase of the Sanger-Zoo project has only looked at mammals and is now expanding to plants, insects and reptiles.
"Social insects like ants are particularly interesting," Kagan said.
"Worker ants and their queen have the same genome, but the queen lives 30 years while the workers last a year or two. This suggests that the queen may have better DNA repair, although there could be other explanations."
Kagan added that their research indicated that the mouse, which is used in cancer experiments, is probably not the perfect model for research because of its very short lifespan.
Something to think about.
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