What causes heart cancer

New hypothesis: why heart cancer is so rare

Montpellier (France) - The lungs, skin and breasts are significantly more susceptible to cancer than other organs such as the heart, brain or pancreas. This is explained on the one hand by the different division activity of stem cells, on the other hand by external factors. The individual organs are exposed to cancer-causing influences such as pollutants, infectious agents or UV radiation to different degrees. An international team of researchers is now presenting another possible explanation: the cancer researchers and evolutionary biologists view the organs of a body as individual ecosystems that either enable or prevent the growth of cancer cells. According to this, vital, smaller organs that do not exist in pairs have developed cancer-inhibiting mechanisms through natural selection, since this serves the biological fitness of the entire organism. In the case of larger organs in pairs, however, this selection pressure was less pronounced. Long-term studies with animals are necessary to test the new hypothesis, the scientists write in the journal "Trends in Cancer".

"The organs that are most important for life support and reproduction could also be better protected against cancer," says Frédéric Thomas from the Center for Ecological and Evolutionary Cancer Research in Montpellier. This is not necessarily the most important factor that explains the organs' different susceptibility to cancer, but it should also be taken into account. One of the internal factors that influence cancer risk is the rate of cell division during tissue regeneration. This value is only low for the heart and brain, for example. In contrast, the inner cell layer of the intestine is completely renewed within a few days. And the more often new cells emerge, the greater the likelihood of mutations that cause cancer. External factors that certainly play an important role are cancer-causing substances that get into the stomach and intestines with food or with the air we breathe into the lungs. The skin, in turn, is exposed to UV radiation from the sun, which increases the risk of cancer in this organ. Alcohol consumption and hepatitis infections promote the development of liver cancer.

As a further, previously neglected factor, Thomas and his colleagues bring the evolution of mechanisms within an organ into play that suppress cancer growth. "Cancer cells are living units - it is impossible that they are not influenced by ecological conditions," says Thomas. The selection pressure for cancer protection may have been different for the individual organs. When tumors develop in a large organ such as the liver or a pair of organs such as the lungs, it has little effect on the entire organism for a long time. The relatively common cancers of the breast and prostate usually only have a disadvantageous effect in old age, as metastases form. The reproductive success would not be impaired. But the body is far less able to tolerate tumors in the brain, heart or pancreas, as these cancers considerably reduce biological fitness.

The organs' different susceptibility to cancer could - also - be the result of a cost-benefit calculation of evolution: For some organs, the cost of cancer protection would pay less than others. The statements of the new hypothesis cannot be verified by evaluating data from studies that have already been completed or with the help of cancer registers, says Thomas. Rather, new long-term studies are needed in which the development of cancer in several organs would have to be followed. In this way, new knowledge for organ-specific cancer prevention and therapy could be gained.

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