How do cancer cells arise?
Biologist Evgeny Cheval on gene mutations, somatic cell functions and diagnosis of stomach cancer
The appearance of a tumor in the first approximation is the process of accumulation of mutations, that is, errors, in the genome of cells. As a rule, these are gene mutations associated with either proliferation (cell division) or apoptosis (programmed cell death).
There are quite powerful, including immune, mechanisms in order to fight genetically modified or changing cells. A cell with damaged DNA must die by apoptosis. But if mutations have occurred that have led to the fact that cells do not easily go into apoptosis, then they have an increased chance of turning into tumor cells.
Oncogenesis is always a process of accumulation of mutations. Several mutations must occur before the properties of the cell change to such an extent that it can be considered a tumor. That is why tumors are more common in the elderly. If gerontology succeeds, we will more often encounter the development of tumors in humans.
The probability that several mutations will occur in one cell, and mutations that will affect well-defined genes, is negligible. Therefore, in addition to the occurrence of mutations, there is a selection of clones, essentially identical to Darwinian natural selection. That is, a mutation occurs, cells multiply. With some probability, another mutation will occur in one of the descendants of the mutated cell, these cells will also share, a mutation will also occur among their descendants, and so on.
If each subsequent mutation increases the ability of cells to reproduce uncontrollably, they get out of control of the body, and the clone formed by such cells gains an advantage. Among the clone cells, after the next mutation, the next clone is selected, which is even more independent of the organism, even less susceptible to programmed cell death, and even more actively proliferates. After the first mutation, we can say that these are abnormal cells, but only from a certain point and after a rather long evolution, they become clinically tumorous.
The purpose of the diagnosis is to catch the tumor before it has reached the point where it can kill the patient. If it is detected in time, it is much easier to fight the tumor.
There are tumors that people shouldn't die from. For example, stomach cancer. It will not be if, after forty years, a gastroendoscopy is performed in due time – a visual examination of the digestive system using a gastroscope. The process of tumor development takes a long time, includes several stages, and it is possible to catch a stage when it is still a polyp that can be removed.
Sometimes cancer cells are called selfish cells. A more successful definition was given by the famous cell biologist Yuri Markovich Vasiliev. He said that cancer cells are cells with antisocial behavior.
It's not just that every normal cell in the body is under very strict control. Any somatic cell in the body serves the purpose of transferring the genetic material contained in the germ cells to the next generation (in humans, one or two cells are usually transferred to the next generation, all the other trillions of cells are needed only for this transfer to take place). All somatic cells are doomed. Therefore, the cell does not need to multiply more than the body needs. And a tumor cell is a cell that behaves asocially: it multiplies more than necessary, not where it is needed, it has properties that are not those that are needed by this tissue. Such a cell really lives for itself.
About the author:
Evgeny Cheval – Doctor of Biological Sciences, Senior Researcher at the Belozersky Research Institute of Physical and Chemical Biology of Moscow State University.
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11.07.2017