Knowing the cause of a disease is the key to curing it. But not all pathologies are so simple. The nature of neoplasms, malignant and benign, is still not thoroughly known to scientists. Oncology is directly involved in its study - a science whose specificity is cancer: study, diagnosis, treatment and prevention. Today, scientists have at their disposal several theories of carcinogenesis. In other words - versions of 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", "genesis".
Hence the definition - a pathological complex phenomenon, the process of both the inception and further progression of a cancerous tumor. Replaces the concept of "oncogenesis".
Process steps
The most common is the theory of multistage 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 followingstages:
- Initiation. Another name is tumor transformation. The first step is an irreversible change in the genome of the somatic cell mass (mutation). It happens very quickly - the account is kept for minutes, hours. The altered cell may be inactive for a long time. Or the process ends at this point.
- Promotion. Interaction between the mutated cell and factors within the organism. Remain modified particles with high reproductive activity. This is a manifestation of the underlying tumor phenotype.
- Progression. The stage is characterized by additional changes in the genome, selection of the most adapted cell clones. The stage of a morphologically obvious cancer that is already capable of metastasizing is characterized by invasive growth.
Mutation theory
This theory of carcinogenesis in the modern world is generally accepted. Cancer begins in the body with one small cell. What is wrong with her? Mutation processes begin to accumulate in specific regions of its DNA. They influence the process of synthesis of new proteins. The elementary unit of the organism begins to produce a new, defective protein substance. And since most of the cells in the body are updated exclusively by division, these chromosomal disorders of the defective cell of the body are inherited by the daughter ones. Those, in turn, pass them on to new ones during their reproduction. A focus of a cancerous tumor appears in the body.
The founder of the mutational theory of carcinogenesis is the German biologist T. Boveri. The very assumption wasexpressed as early as 1914. Boveri stated that the cause of cancer is chromosomal changes in cells.
Over the following years, colleagues supported his position:
- A. Knudson.
- G. Muller.
- B. Vogelstein.
- E. Faron.
- R. Weinberg.
These scientists have been finding evidence for decades that cancer is a consequence of cellular gene mutations.
Random mutations
This theory of carcinogenesis in some aspects is similar to the position of Boveri and his associates. Its author is scientist L. Loeb, an employee of the University of Washington.
The specialist argued that, on average, in each cell during its entire life, a mutation can occur in only one gene. But in some cases, their (mutation) frequency increases. Oxidants, carcinogens (environmental factors that directly cause cancer) or disturbances in the processes of repair and replication of DNA itself contribute to this.
L. Loeb argued that cancer is always a consequence 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 it is very difficult to somehow confirm or refute what he has stated.
Thus, in this case, oncogenesis is regarded as a consequence of cellular mutations that provide this cell with advantages in division. Chromosomal rearrangements in the framework of this theory of carcinogenesis, tumors are already assigned a side value.
Early chromosomal 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 came 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 an altered number of chromosomes. This observation allowed them to assert that early chromosomal instability leads to mutation processes in oncogenes, tumor suppressors.
This theory is based on the instability of the genome. This factor, coupled 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 the scientist P. Duesberg, who works at the University of California, USA. According to him, cancer is only a consequence of aneuploidy. Mutations observed in specific genes do not play any role in the process of carcinogenesis.
What is aneuploidy? These are changes due to which cells begin to differ in the number of chromosomes, in no way a multiple of their main set. In modern times, this also includes the elongation / shortening of chromosome threads, their translocation - the movement of large sections.
Naturally, the vast majority of aneuploid cells will die. But for some of the survivors, the number (and it is already measured in thousands) of genes will not be the same as for normalcells. The result is the disintegration of a team of enzymes, whose coordinated work ensured the synthesis and integrity of DNA, the appearance of a mass of breaks in the double helix, which further destabilize the genome. The higher the level of aneuploidy, the more unstable the cell, the more likely the appearance of the "wrong" particle that will exist and divide 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 chromosome distribution than to mutational processes.
Fetal
One of the widely presented theories of carcinogenesis in oncology is embryonic. Linking cancer development to germ cells.
Several scientists of different years expressed their assumptions on this matter. Let's briefly get acquainted with their views:
- J. Conheim (1875). The scientist put forward the hypothesis that cancer cells develop from embryonic ones. But only of those that turned out to be unnecessary during the development of the embryo.
- B. Rippert (1911). His assumption is based on the fact that an altered environment may allow the embryonic cell to "hide" from the body's control system over its development and further reproduction.
- B. Rotter (1927). The scientist expressed the following hypothesis: primitive embryonic cells can somehow settle in the organs, tissues of the body in the process of its embryonic development. These particles will become the focus of neoplasm 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 these particles that have activated oncogenes.
The main proven fact that confirms the theory is the ability of tumor cells to normalize during their differentiation. This allowed us to approve laboratory studies on mice. Even cancer cells with an altered chromosome set normalize during differentiation.
Many things are connected in the tissue theory - carcinogenic profile, degree of rejuvenation, changes in functions, structures of homeostasis, modes of proliferation, uncontrolled growth of clonogenic particles of the body. All this combination eventually 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 a virus that causes cancer is important (unlike a normal infection) only at a very early stage. It causes hereditary changes in the cell, which are later transferred to the children on their own, without his participation.
The viral nature of some cancers has already been proven by scientists. This is the Rous virus that causes sarcoma in chickens, the filtering agent that causes Shoup's papilloma in rabbits, the milk factor is the cause of breast cancer in mice. Total of these diseasesabout 30 vertebrates have been studied today. With regards to people, these are papillomas and condylomas, which are transmitted from person to person through sexual, domestic contact.
Scientists also know viruses that can cause various types of leukemia in mice. This is the virus of Friend, Gross, Moloney, 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, which are isolated from tumor viruses. It (acid) introduces additional genetic data into the cell, which causes malignancy of the particle.
The fact that a chemical substance (nucleic acid) is the cause of the formation of a tumor brings this version closer to the polyetiological one. And this is already 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 are chemical environmental factors. Scientists divide them into several groups:
- Genotoxic carcinogens. They will react directly with the DNA.
- Epigenetic carcinogens. They cause changes in chromatin, the structure of DNA, without affecting its very sequence.
External causes in the framework of 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 kindradiation - ionizing, radiation. The effect of radionuclides on organisms deserves great attention.
- Biological.
Other theories
In the modern scientific world, there are also the following theories of the appearance and development of cancerous tumors:
- Epigenetic.
- Immune.
- Cancer stem cells.
- Evolutionary.
The reader is now familiar with both the concept of "carcinogenesis", the stages of development of a cancerous tumor, and with the main theories of oncogenesis. The most recognized of them today is mutational. The future of the scientific world lies in the development of a unified theory that will help humanity defeat this terrible disease forever.
