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Cold discomforts: increase in cancer rates and adaptation of life in extreme environments



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IMAGE: Earth maps showing that the lowest "average annual temperature" correlates with the highest incidence of cancer in the world.
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Credit: Konstantinos Voskarides, University of Cyprus School of Medicine

It is well known that the incidence of cancer is increasing worldwide, with foci of human populations and seemingly larger geographic locations risk than others.

The researcher Konstantinos Voskarides, Ph.D., of the School of Medicine of the University of Cyrpus, pointed out that populations living at very low temperatures, as in Denmark and Norway, had one of the highest incidences of cancer in the world.

Now, in a new article in the advanced online edition of the journal Molecular Biology and Evolution has presented a new hypothesis: there is an evolutionary relationship between adaptation in extreme environmental conditions, such as cold and high altitude ̵

1; and increased risk of cancer in humans.

"The findings of this study provide evidence that genetic variants that are considered beneficial in extreme environments may also predispose to cancer," Voskarides said. "Cellular resistance at low temperatures and at high altitude probably increases the likelihood of malignancy, and this effect could hardly be filtered by natural selection, since most cancers appear later when most people have children."

Voskarides focused on the effect of low temperatures, either in Arctic / Scandinavian climates or at high altitudes. Voskarides' analyzes focused on the relationship between cancer risk and average annual local temperatures. He concluded that the extremely cold environment contributed to the risk of cancer.

For this, Voskarides carefully examined the most accurate and reliable data on the worldwide incidence of cancer (the GLOBOCAN-2012 database allows a variety of incidence / prevalence analyzes by country or by type of cancer, as well as screening Through genetic clues among 247 different cancer genome association studies, he also researched available bibliography on cancer incidence and genetic data for human populations living in conditions of extreme cold and extreme altitudes.

surprising pattern, with the highest incidence of certain cancers linked to populations living in the coldest environments.In addition, the analysis of 186 human populations showed a high linearity of high incidence of cancer with the lowest environmental temperature.

" These data show that these populations exhibit an extremely high incidence of cancer, esp especially for lung, breast and colorectal cancer, "said Voskarides.

The genetic evidence was also clear and highly significant. Genes that are selected for populations in order to survive in extreme environmental conditions also predispose to cancer.

Among the most important cancer associations with genes under selection are colorectal cancer for Native Americans and Siberian Eskimos, cancer of the esophagus and lung cancer for Siberian Eskimos, leukemia for Oromi (a high altitude population in Ethiopia) and a variety of high-altitude dwelling Andeans-Tibetans cancers.

"Evidence was found that cancer rates have increased in those populations through natural selection procedures," Voskarides said. "This is the first study that provides evidence that a high risk of cancer can be the result of an evolutionary adaptation in certain environmental conditions."

Another finding of this study is that natural selection has especially favored tumor suppressor genes in these populations instead of oncogenes. This is in agreement with previous studies that showed that mutations in p53 (the most frequently mutated gene in cancers) help animals survive at high altitudes.

"It seems that the populations segregated under the concept of extreme environment: extreme risk cancer," said Voskarides.

For scientists pursuing the confluence of the environment and genetics on cancer risk, the new study will open a new avenue to explore some of the key adaptive forces that could be driving the epidemiology of cancer.

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