To know the cause of the disease is to have a key to curing it. But not with all pathologies, everything is so simple. The nature of neoplasms, malignant and benign, is still not known to scientists thoroughly. Oncology is directly involved in its study - a science whose specificity is cancer: study, diagnosis, treatment and prevention. To date, scientists have at their disposal several theories of carcinogenesis. In other words, versions on the origin and development of a cancerous tumor in the body. Let's get to know them.
Carcinogenesis - what is it
The word comes from lat. cancerogenesis. This is a combination of two concepts - “cancer” + “development”, “nucleation”.
Hence the definition - a pathological complex phenomenon, the process of both the nucleation and further progression of the cancerous tumor. Replaces the concept of oncogenesis.
Process stages
The most common is the theory of multi-stage carcinogenesis. In other words, a cancerous tumor always develops, passing through several specific stages, according to the same algorithm in all organisms. These are the following stages:
- Initiation. Another name is tumor transformation. The first step is an irreversible change in the genome of somatic cell mass (mutation). It happens very quickly - the account is kept for minutes, hours. An altered cell can be inactive for a long time. Or the process on this is completely terminated.
- Promotion The interaction between a mutated cell and factors within the body. Remained particles with high reproductive activity remain. This is a manifestation of the main phenotype of the tumor.
- Progression. The stage is characterized by additional changes in the genome, selection of the most adapted cell clones. The stage of a morphologically obvious cancerous tumor, which is already capable of metastasizing, is characterized by invasive growth.
Mutation theory
This theory of carcinogenesis in the modern world is considered universally recognized. Cancer begins to develop in the body with one small cell. What is wrong with her? Mutation processes begin to accumulate in specific areas of her DNA. They affect the synthesis of new proteins. An elementary unit of the body begins to produce a new, defective protein substance. And since most of the cells in the body are updated exclusively by division, these chromosomal abnormalities of the defective cells of the body are inherited by the daughter. Those, in turn, pass them on to new ones when they breed. In the body, a focus of a cancerous tumor appears.
The founder of the mutational theory of carcinogenesis is a German biologist T. Boveri. The very assumption was made by him back in 1914. Boveri stated that the cause of cancer is chromosomal changes in the cells.
Over the next years, his position was supported by colleagues:
- A. Knudson.
- G. Muller.
- B. Vogelstein.
- E. Faron.
- R. Weinberg.
For decades, these scientists have found evidence that cancer is a consequence of cellular gene mutations.
Random mutations
This theory of carcinogenesis in some aspects is similar to the position of Bowery and his associates. Its author is a scientist L. Loeb, an employee of the University of Washington.
The specialist argued that, according to average indicators, in each cell over its entire life a mutation can occur in only one gene. But in some cases, their (mutations) frequency increases. Oxidants, carcinogens (environmental factors that directly cause cancer) or disturbances in the repair and replication of DNA itself contribute to this.
L. Loeb argued that cancer is always the result of a huge number of mutations per cell. So, on average, their number should reach 10-100 thousand! But the author himself also admits that somehow it is very difficult to confirm or refute what he claimed.
Thus, in this case, oncogenesis is regarded as a consequence of cell mutations that provide the cell with division benefits. Chromosomal rearrangements within the framework of this theory of carcinogenesis, tumors are already given a secondary value.
Early chromosome instability
The authors of this theory are scientists B. Vogelstein and K. Lingaur. It belongs to the modern theories of carcinogenesis, proclaimed in 1997.
Scientists have come up with a new idea as a result of practical research. They found that in the malignant formation of the rectum there are many cells with precisely the changed number of chromosomes. This observation allowed them to argue that early chromosomal instability leads to mutational processes in oncogenes, cancer suppressors.
This theory is based on genome instability. This factor, together with all known natural selection, can lead to the appearance of a benign neoplasm. But sometimes it transforms into a malignant tumor that grows with metastases.
Aneuploidy
Another noteworthy theory of carcinogenesis. Its author is a scientist P. Duesberg, a laborer at the University of California, USA. According to his assumption, cancer is a consequence of only aneuploidy. Mutations observed in specific genes do not play any role in carcinogenesis.
What is aneuploidy? These are changes due to which the cells begin to differ in the number of chromosomes that are not at all a multiple of their basic set. In modern times, this also includes lengthening / shortening of chromosomal filaments, their translocation - the movement of large sections.
Naturally, the vast majority of aneuploid cells will die. But part of the survivors the number (and it is already measured in thousands) of genes will not be the same as that of normal cells. The consequence is the collapse of the enzyme team, whose coordinated work ensured the synthesis and integrity of DNA, the appearance of a mass of breaks in the double helix, which already further destabilize the genome. The higher the level of aneuploidy, the more unstable the cell, the greater the likelihood of the appearance of an “irregular” particle that will exist and share in any part of the body.
The essence of the theory is that the appearance and development of a malignant tumor is more due to errors in the chromosomal distribution than to mutational processes.
Fetal
One of the widely presented theories of carcinogenesis in oncology is embryonic. Binding the development of cancer with germ cells.
Several scientists from different years expressed their assumptions in this regard. Briefly get acquainted with their views:
- J. Congame (1875). The scientist hypothesized that cancer cells develop from embryonic. But only of those that were unnecessary in the process of embryo development.
- V. Rippert (1911). His assumption is based on the fact that the altered environment may allow the embryonic cell to “hide” from the body’s control system over its development and further reproduction.
- W. Rotter (1927). The scientist expressed the following hypothesis: primitive embryonic cells can somehow settle in the organs and tissues of the body in the process of its embryonic development. These particles will become the focus of tumor development in the future.
Fabric
One of the recognized authors of the tissue theory of carcinogenesis is the scientist Yu. M. Vasiliev. According to his views, the cause of the development of a cancerous tumor is a violation of the control of the tissue system over the proliferation of clonogenic cells. But it is precisely these particles that have activated oncogenes.
The main proven fact confirming the theory is the ability of tumor cells to normalize during their differentiation. This allowed to confirm laboratory studies in mice. Even cancer cells with an altered chromosome set normalize during differentiation.
In tissue theory, much is associated - a carcinogenic profile, degrees of rejuvenation, a change in functions, the structure of homeostasis, proliferation modes, and uncontrolled growth of clonogenic particles of the body. All this combination ultimately leads to the formation of a malignant tumor.
Viral
The viral theory of carcinogenesis is also popular in the scientific world. It is based on the following - for the appearance and development of a cancerous tumor, the presence in the body of the virus that causes cancer is important (in contrast to the usual infection) only at an early stage. It causes hereditary changes in the cell, which are subsequently passed on to the daughter independently, without his participation.
The viral nature of some cancers has already been proven by scientists. This is the Routh virus, which causes sarcoma in chickens, a filtering agent that causes the Shaw papilloma in rabbits, and the milk factor is the cause of breast cancer in mice. In total, about 30 such vertebral diseases have been studied today. With regards to people, these are papillomas and condylomas, which are transmitted from person to person through sexual, domestic means.
The viruses are also known to scientists, which can cause various types of leukemia in mice. This is the virus of Friend, Gross, Moloni, Mazurenko, Grafi.
As a result of research, experts also came to the conclusion that a malignant formation of a viral nature can also be caused artificially. This requires nucleic acids that are isolated from tumorigenic viruses. It (acid) introduces additional genetic data into the cell, which causes malignancy of the particle.
The fact that the cause of the formation of a tumor is a chemical substance (nucleic acid), brings this version closer to the polyetiological one. And this is a step towards the development of a unified theory of the origin of cancer formation.
Chemical theory
According to her, the main cause of cellular mutations that lead to the development of cancer is the chemical environmental factors . Scientists divide them into several groups:
- Carcinogens are genotoxic. They will react directly with DNA.
- Carcinogens are epigenetic. They cause changes in chromatin, the structure of DNA, without affecting its very sequence.
External causes in the theory of chemical carcinogenesis are divided into the following groups:
- Chemical. Aromatic amines and hydrocarbons, asbestos, mineral fertilizers, insecticides, pesticides, herbicides.
- Physical. This is a different type of radiation - ionizing, radiation. Of great interest is the effect on radionuclide organisms.
- Biological.
Other theories
In the modern scientific world, the following theories of the appearance and development of cancerous tumors also exist:
- Epigenetic.
- Immune
- Cancer stem cells.
- Evolutionary.
The reader is now familiar with the concept of "carcinogenesis", the stages of development of a cancerous tumor, and with the basic theories of oncogenesis. Recognized of them today is mutational. The future of the scientific world is the development of a unified theory that will help humanity to defeat this terrible disease forever.