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Wednesday, May 22, 2024

Why don’t whales get cancer? Researchers are getting closer to solving the mystery

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British scientists have probably solved one of the most surprising mysteries of medicine – why some species of animals develop cancer, and others do so very rarely.

According to scientists from the Cancer, Aging and Somatic Mutations Program at the Wellcome Sanger Institute, researchers have succumbed to the suggestions of Peto’s paradox for many years. This is statistical analysis, named after its discoverer Richard Peto. He described the hypothesis that a random mutation could make any cell capable of rapidly becoming cancerous. Therefore, the more cells, the greater the risk of cancer. According to “The Guardian”, the paradox has been one of the subjects of the program’s research for many years. Its members are supported by a wide variety of research centres, such as the Zoological Society of London (ZSL). Detailed research on this subject was published in the scientific journal “Nature”.

“Cancer is a disease that occurs when a cell in the body undergoes a series of mutations in its DNA and begins to divide uncontrollably, and the body’s defense system is unable to stop this growth,” said Alex Cagan of the Wellcome Sanger Institute. “The more cells an animal has, the greater the risk that one of them will become cancerous.”

– Think of mobile phones as lottery tickets – the more you have, the greater your “chance of winning”. This is the case with disease. So if there is an organism with a thousand times more cells than a human, then the risk of cancer is a thousand times higher, agreed Simon Spiro, a veterinary pathologist at ZSL.

For researchers, the biggest mystery was the massive animals. “Given everything we know about cancer in humans, some of the larger species shouldn’t even exist.” For example, whales have trillions more cells than we do. If we take the somatic mutation rate from humans and apply it to whales, they should develop cancer even before they reach adulthood. And that doesn’t happen […] Large, long-lived animals like whales and elephants make us question our assumptions about cancer and somatic evolution, Cagan added.

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First huge differences, at the end of life a similar number

To better understand this paradox, the team from the Sanger Institute studied 16 species of animals, including lions, tigers, giraffes, ferrets, lemurs, sand mollies and mice from various UK zoos.

“What we discovered was shocking. The variation in the number of mutations the animals accumulated each year was huge. They found that long-lived species accumulate mutations at a slower rate, while short-lived species do so at a faster rate. For example, there are about 47 mutations per year in humans and about 800 mutations per year in mice. These rodents live about four years. Meanwhile, the average human life expectancy is 83.6 years, Cagan said.

The mouse – as we know – is much smaller than a human or the aforementioned whale, and thus – has fewer cells. So scientists wondered why mice are more susceptible to cancer. The answer to this question may have appeared with subsequent results.

About three thousand mutations were found in all animal species that were involved in the study at the end of life, the researchers said. ‘The similar number of mutations towards the end of these animals’ lives is striking, although it is not yet clear whether this is due to their aging,’ he added.

However, scientists do not rule out that the lifespan of a given animal may play an important role in “slowing down” the cancer. After all, mice can live up to four years, and whales or elephants can live for several decades, and still have the same number of cancerous DNA mutations at the end of their lives. However, it is not clear where this ability may come from. As pointed out by The Guardian, the relationship between mutation rate and lifespan has only been studied for animals that have short or medium lifespans.

“We can only study creatures that have died a natural death, and these very long lifetimes will be rare by definition. We will have to wait for such data to be obtained – explained Spiro.

Bowhead whale (Balaena mysticetus)Adobe Stock

They want further analysis

The first phase of the project focused exclusively on mammals. Scientists now want to extend the research to plants, insects and reptiles, and see if their hypotheses apply to other groups of organisms as well.

– Of particular interest are social insects such as ants. Workers and their queen share the same genome, but the queen lives up to 30 years and the workers a year or two. This suggests that the queen may show better repair in her DNA, although there may be other explanations, added Cagan.

In the next part of the analysis, the scientists intend to take a closer look at animals that live much longer. They add that they may be better models for understanding the protective processes against cancer. The key point, however, will be finding a link between mutation rates, tumors and ageing, which will offer a new understanding of both processes and could lead to improved cancer research and treatment.

The Guardian, sangerinstitute.blog

Main photo source: Adobe Stock

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