In order for living beings to maintain a normal and healthy life, all organs of the body must function normally. The basis of the proper activity of the organs actually depends on the behavior of the cells in the organ and the mechanisms within the cells.
In particular, the very careful regulation of cell production; The differentiation or specialization of cells into certain cell types is important. Any failure in the division and differentiation and programmed death of cells creates problems in balancing the number of cells in tissues and organs. In this case, it means the formation of cancer as a result of excessive proliferation of cells and their reproduction without specialization.
Although many types of cancer make it difficult to understand, prevent, diagnose and treat, most, and perhaps all, cancers have a few characteristics in common. The first feature that appears in all cancers is excessive cell proliferation and undifferentiation. In fact, all these cancerous changes are due to mutations in proto-oncogene, tumor suppressor and DNA repair genes. In such cases, proto-oncogenes gain oncogene activity and tumor suppressor and repair genes lose their activity. These mechanisms are rearrangement in chromosomes, genetic material gain (insertion), loss (deletion), point mutation and gene amplification changes in genes. Although mutations in genes start with the formation of a mutation in the initial stages, hundreds of mutations are required to reach the stage of cancer. Normal cells inhibit density-dependent cell proliferation, and cell division stops when the cell population reaches a certain number. Similarly, normal cells show contact inhibition. However, contact inhibition does not appear in cancer cells.
At the same time, for cancer cells to grow excessively, growth factors reach these cells in excess of the required amount. The reason for this is the abnormal increase of growth factors receptor molecules on cancer cells. Another possibility is that cancer cells do not need extracellular growth factors at all and make the factors necessary for their own growth and are insensitive to growth suppressing factors. All these causes ensure the uncontrolled division of the cell.
Another feature of the cancer cell is invasion and metastasis. This is due to changes in the cytoskeleton and changes in cell-cell and cell-matrix communication molecules on the cell. Cancer cells do not adhere to neighboring cells and matrix elements in the tissue, and also do not show a regular shape due to the cytoskeleton change, and in this case, they easily pass from the endothelial cell spaces of the vessels into the vessels and cause distant organ metastases. Of course, this situation is often hindered by immune cells, and only one cell out of every 10000 cancer cells that enter the vessels can reach other organs and form metastases.
On the other hand, due to cellular skeletal change, it allows transition from other cells of the tissue to nearby tissues and organs, and in this case, it migrates or invades. The reason why cancer cells do not adhere to each other is that the adhesion molecules on the cell change and lose their ability to adhere, as well as the protease production of cancer cells and the deterioration of these adhesion proteins.
Another feature of the cancer cell is its angiogenesis ability. Cancer cells can secrete growth factor that promotes angiogenesis. In this case, it may cause the mass to form vessels and establish contact with the peripheral circulation. Thus, it provides the necessary nutrients and oxygen from the peripheral circulation for its growth and adds the waste material of its metabolism to the circulation. At the same time, it contributes to the metastasis through the vein.
Finally, normal cells have a limited lifespan and timely programmed death occurs, but this feature is absent in cancer cells.
They do not die because they ignore the escape from the immune system and cellular signals by changing the proteins on the cancer cell. DNA damage in the normal cell triggers programmed cell death and thus the negative effect of mutation is prevented, but the cancer cell does not respond to apoptosis signals, cell death does not occur and continues to divide with faulty DNA. Thus, with each division, new DNA mutations arise. In addition, thanks to the telomerase enzyme in cancer cells, the telomere regions of the chromosomes are constantly renewed and the cell becomes immortal.
The basic functional properties of the cancer cell were determined by Hanahan and Weinberg in 2000.
They listed the reasons why the cancer cell behaves differently from the normal cell as 6 important factors:
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Cancer cell generates growth signals by itself and causes autocrine stimulation,
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Responds to growth suppressing signals and becomes insensitive to them.
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It has the ability to reproduce uncontrollably,
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Provides escape from apoptosis
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It has the ability to migrate or invade surrounding tissues and metastasize to distant organs,
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It is connected to the peripheral circulation due to new vessel formation.
In recent years, a 7th feature has been added to these features.
7. It is the inflammatory microenvironment of the cancer cell and because cancer is a chronic inflammation, it develops a helpful microenvironment to the cancerous cells.
In fact, all these features are the characteristics of cells in the embryo. However, normally in the embryo, cell proliferation results in differentiation and a tissue and organ are formed, and when the time comes, the death mechanisms in the cells are activated. Although cancer cells have the ability to divide in stem cells, they are insensitive to death signals and this causes their abnormal growth. All drugs and treatment methods produced for cancer treatment are actually designed based on the characteristics of cancer cells. Therefore, new features and mutations in cancer cells are of great importance for new cancer drugs to be found in the future.
Öğr. Gör. Masoumeh Hassani
