Stem cells and cancer
The probability of cancer depends on the activity of stem cells
Kirill Stasevich, "Science and Life" based on Johns Hopkins University materials:
Bad luck plays larger role than environmental, genetic factors in determining who gets cancerIt is known that different types of cancer have different probabilities: according to statistics, lung tumors are 11 times ahead of brain tumors.
Usually such a difference is explained by the influence of lifestyle, ecology or poor heredity. That is, lung cancer may occur more often due to smoking or, for example, due to the fact that the genetic abnormalities associated with it are better fixed in generations than in the case of brain cancer. However, neither ecology with bad habits nor bad heredity fully explain why malignant tumors occur with different probability in different tissues.
Researchers from Johns Hopkins University (USA) have concluded that the third and, apparently, the main factor determining the likelihood of cancer is the number of stem cell divisions. The tissues of the body are constantly updated due to the reserve of their own stem cells in the blood, they are one, in the intestinal epithelium – others, in the skin – others, etc. Their rate of division is different, and the number of divisions that a stem cell undergoes during its lifetime is also different. And, as Christian Tomasetti and Bert Vogelstein write in Science (Variation in cancer risk among tissues can be explained by the number of stem cell divisions), 65% of the differences between different tissues regarding the likelihood of cancer are due precisely to the fact that in some tissues stem cells divide more energetic than in others.
The more cell divisions accumulated in the stem cell population, the greater the probability of malignant tissue degeneration – this rule works even for tumors with a 100,000-fold difference in probability. So, the rarest tumors occur in the bones of the head, pelvis and forearm – and indeed, stem cells are the most inactive here. Most often they are divided in the basal layer of the epithelium (due to the basal layer, skin renewal occurs), as well as in the colon and rectum – and tumors in them are among the most common.
Most of the ordinary, differentiated cells that make up the bulk of a tissue or organ do not live too long (as an exception, we can recall, for example, neurons). Therefore, even if they accumulate many potentially oncogenic mutations, the disease will not begin: the cell will die before it has time to provoke cancer. Stem cells, on the contrary, live for a long time, divide many times and can give rise to a tumor. The more a cell divides, the more likely it is that the oncogenic mutation that once got into it will work: in it and in its clone descendants. (Obviously, in the case of brain tumors, we should not talk about the division of stem cells, of which there are too few in it, but about the division of service glial cells.)
Of course, this does not cancel out either a bad ecology (so in the text – VM), or an unhealthy lifestyle. The number of cell divisions is something like an amplifier of unfavorable factors, and in some tissues such an "amplifier" works poorly, and in others – at full capacity. That is, if we have two tumors that differ greatly in frequency, then, as mentioned above, 65% of the differences may be due to a difference in the activity of stem cells, and all other percentages can be attributed to external factors (well, or to heredity).
Graph from an article in Science – VM
From a practical point of view, the new data should help in the diagnosis and prevention of oncological diseases. It is worth noting, however, that, analyzing the statistics of tumors and the rate of cell division in 31 tissues, the authors of the work did not take into account breast cancer and prostate cancer. The problem is that there is still no reliable information about the activity of stem cells in the mammary and prostate glands. However, it is this problem that researchers are going to address in the near future – because breast and prostate tumors are, unfortunately, one of the most common.
Portal "Eternal youth" http://vechnayamolodost.ru13.01.2015