- Adaptation to extreme environmental conditions - like cold and high altitude is associated with an increased cancer risk in humans.
- Cell resistance at low temperatures and at high altitude probably increases the probability of malignancy.
- Genetic variants that adapt to extreme environments, can also predispose for cancer.
The risk of developing cancer may be higher in those who live in cold regions.
According to a study published in the journal Molecular Biology and Evolution, populations living in very low temperatures, like in Denmark and Norway, had among the highest incidences of cancer in the world.
There is an evolutionary relationship between adaptation to extreme environmental conditions - like cold and high altitude - and increased cancer risk in humans.
"Cell resistance at low temperatures and high altitude probably increases the probability of malignancy. This effect hardly could be filtered out by natural selection since most cancers appear later on in age after most people have their children," said Voskarides.
Low temperature and cancer Risk
The research team focused on the effect of low temperatures, either within Arctic/Scandinavian climates or high altitudes.
Their analyses focused on the relationship between cancer risk and local average annual temperatures. They concluded that the extremely cold environment contributed to the cancer risk.
For the study, they carefully examined the data of worldwide cancer incidence. They probed the available literature bibliographic cancer incidence and genetic data for human populations living at extreme cold and extreme high-altitudes.
Genetic Data Related To Cancer Risk
Konstantinos Voskarides, Ph.D., of the Univesity of Cyrpus' Medical School, focused on the effect of low temperatures, either within Arctic/Scandinavian climates or high altitudes. Voskarides' analyses focused on the relationship between cancer risk and local average annual temperatures. He concluded that the extremely cold environment contributed to the cancer risk.
Voskarides carefully examined the most accurate and reliable data of worldwide cancer incidence (the GLOBOCAN-2012 database permits a variety of incidence/prevalence analysis per country or per cancer type , as well as sifting through genetic clues among 247 different cancer genome-wide association studies.
Additionally, he probed the available literature bibliographic cancer incidence and genetic data for human populations living at extreme cold and extreme high-altitudes.
A striking pattern began to emerge, with the highest incidence of certain cancers linked to those populations living in the coldest environments. Additionally, analysis of 186 human populations showed a great linearity of high cancer incidence with the lower the environmental temperature.
"These data show that these populations exhibit extremely high cancer incidence, especially for lung, breast and colorectal cancer," said Voskarides. The genetic evidence was also clear and highly significant. Genes that are under selection to populations in order to survive under extreme environmental conditions, also predispose to cancer.
Among the highest cancer associations with genes under selection is:
- Colorectal cancer for Natives Americans and Siberian Eskimos,
- Esophageal cancer and lung cancer for Siberian Eskimos
- Leukemia for Oromi (a high-altitude population in Ethiopia)
- A variety of cancers for high-altitude dwelling Andeans-Tibetans.
Another finding of this study is that natural selection has favored especially tumor suppressor genes in those populations instead of oncogenes. This is in accordance with previous studies that showed that mutations in p53 (the most frequently mutated gene in cancers) help animals to survive at very high altitude.
"It seems that the populations segregated under the concept of extreme environment - extreme cancer risk," said Voskarides.
For scientists pursuing the confluence of the environment and genetic on cancer risk, the new study will open a new avenue for exploring some of the key adaptive forces that could be driving cancer epidemiology.
- Konstantinos Voskarides. 'Combination of 247 genome-wide association studies reveals high cancer risk as a result of evolutionary adaptation.' Molecular Biology and Evolution (2017). https:doi.org/10.1093/molbev/msx305.