Epidemiology and statistics of neoplasms
Tumor processes represent one of the most frequent and socially significant groups of diseases in modern medicine. In developed countries worldwide, they securely occupy second place among all causes of death, second only to cardiovascular diseases.
According to official statistical data from the World Health Organization (WHO), the epidemiological picture is as follows:
- Incidence: more than 6 million new cases of tumors are registered worldwide annually.
- Mortality: about 5 million people die from oncological diseases every year (with the European Region accounting for approximately 1.7 million of these deaths).
Sexual dimorphism plays an important role: statistics inexorably show that men develop the disease 1.5 times more frequently than women.
Morbidity structure depending on localization:
- General population: lesions of the lungs, stomach, prostate gland, and colon lead.
- In men (about 75% of all diagnosed cases): neoplasms of the lung, stomach, prostate gland, and colon are most common.
- In women (accounting for 75% of cases in the female population): breast cancer, stomach cancer, uterine cancer, colon and rectal cancer, as well as various skin lesions predominate.
Main theories of etiology and pathogenesis
To date, medical science lacks a single, absolutely exhaustive concept of tumor origin. Historically and clinically, several fundamental theories have formed to explain the etiology and pathogenesis of neoplastic processes:
- Irritation theory (proposed by R. Virchow).
It is based on the premise that the main cause of tumor transformation is the chronic, prolonged exposure of normal body tissues to various irritating substances.
- Embryonic origin theory (developed by J. Cohnheim).
According to this concept, specific "dormant" cells of embryonic origin persist in the tissues of the adult organism. Under the aggressive influence of mechanical or chemical irritants, these cells are activated and begin to multiply intensively. The result of this process is the unbridled growth of the atypical cell pool and the formation of a tumor node.
- Viral-immunogenetic theory (authored by L. Zilber).
It describes the process as follows: specific oncogenic viruses invade a healthy cell, leading to the formation of an oncogene. As a result, the normal physiological regulation of cell division is critically disrupted. Meanwhile, various external chemical and physical factors act as catalysts, significantly enhancing the activity of the invading viruses.
- Polyetiological theory.
This is a modern concept globally recognized by the medical community. It asserts the multi-causal development of any neoplasms. Pathogenesis is viewed as a complex, synergistic combination of prolonged exposure to external carcinogens, hereditary genetic factors, and the activity of oncogenic viruses.
Classification of carcinogenic factors
Based on WHO data, a clear ratio of the causes of tumor transformation can be distinguished: the vast majority (90%) is caused by the action of external oncogenic factors, and only 10% are associated with endogenous genetic changes and isolated virus exposure.
All known external factors are traditionally divided into three large groups:
- Physical factors: ionizing radiation holds key pathogenic significance in this group, as it is capable of directly damaging the cellular genome.
- Chemical factors: primarily polycyclic aromatic hydrocarbons (e.g., benzpyrene, benzidine, and other toxic compounds). The main domestic and industrial sources of these substances are tobacco smoke, various tars, and internal combustion engine exhaust gases.
- Biological factors: represented by specific oncogenic viruses capable of integrating into the host cell's DNA.
It is important to note that carcinogenesis is a protracted process. Malignant tumors developing under the influence of the described oncogenic substances have a prolonged latent period, which averages from 15 to 20 years.
Briefly: answers to topical questions
What types of atypia are characteristic of malignant neoplasms?
Malignant neoplasms are characterized by four main types of atypia (from Greek atypicus).
- Morphological — expressed as a disruption of tissue and cellular structure, subdivided into tissue and cellular atypia.
- Biochemical — manifests as changes in the metabolism of the tumor cell (dominance of anaerobic glycolysis, alterations in protein and nucleic acid synthesis).
- Antigenic — characterized by the appearance of new antigens or the loss of tissue-specific antigens.
- Functional — consists of the loss of specialized functions of the precursor cell or the acquisition of an uncharacteristic function.
What stages are distinguished in the pathogenesis of tumor growth (carcinogenesis)?
The following stages are distinguished in carcinogenesis:
- Initiation — the interaction of a genotoxic carcinogen with the cell genome, causing genomic rearrangement; the process is irreversible.
- Promotion — the action of an additional damaging agent—a promoter, as a result of which the cell undergoes malignant transformation and begins to divide uncontrollably.
- Progression.
- Outcome.
The classical model of tumor pathogenesis also distinguishes clonal propagation and metastasis; moreover, metastasis can occur at early stages of carcinogenesis.
Which specific oncogenic viruses belong to biological carcinogens?
Biological carcinogens include:
- DNA viruses: papillomaviruses, polyomaviruses, vacuolating virus, herpesviruses, Epstein-Barr virus, cytomegalovirus, and hepatitis viruses. These include high-risk human papillomaviruses.
- RNA viruses (retroviruses), which synthesize a DNA copy using reverse transcriptase that integrates into the host genome.
- Endogenous viruses, fragments of the human genome similar to retroviruses and capable of being activated.
Which groups of chemical carcinogens are distinguished in the etiology of neoplasms?
Chemical carcinogens are classified by their chemical nature into two large groups:
- Organic compounds — polycyclic aromatic hydrocarbons, heterocyclic aromatic hydrocarbons, nitroso compounds, aminoazo compounds, epoxides, aflatoxins, aromatic amines, and amides.
- Inorganic compounds — arsenic, beryllium oxide, chromates, cobalt.
According to their interaction with DNA, they are divided into:
- Genotoxic — polycyclic aromatic hydrocarbons, aromatic amines, nitroso compounds.
- Epigenetic.
Which endogenous risk factors contribute to the development of tumors?
A number of endogenous risk factors and mutagens contribute to the development of tumors.
- Hereditary predisposition — defects in antioncogenes, DNA repair systems, and apoptosis.
- Immunodepression — defects in cellular or humoral immunity.
- Hormonal imbalance — prolonged hyperestrogenemia and the influence of the menopausal period.
- Chronic inflammation — accompanied by changes in cytokine status.
- Hyperplastic processes — proliferation of glandular epithelium.
- Endogenous chemical carcinogens — aromatic amino acids, steroid hormones, bile acids, pro-inflammatory cytokines, reactive oxygen species.
- Endogenous mutagens — excess of free radicals, lipid peroxidation products, and certain metabolites.
For quick memorization of the theories of origin, use associations based on the first letters of the authors' surnames: Virchow — Impact (irritation), Cohnheim — Cells (embryonic), Zilber — Infection (viruses).
Class and exam questions
What does the term "independence (autonomy)" mean when applied to a tumor?
Autonomy means that the growth, development, and metabolism of the neoplasm occur independently of the regulatory systems (nervous, endocrine, immune) of the body itself.
Which theory of tumor etiology is currently universally accepted?
Modern medicine relies on the polyetiological theory, which explains the development of neoplasms by the combined impact of genetic, viral factors, and external carcinogens.
Which physical factor plays the greatest role in the development of neoplasms?
According to the classification of risk factors, ionizing radiation has the primary and most destructive significance among physical agents.
What else to study on this topic
- Clinical differences between benign and malignant tumors
- Types of neoplasm growth: expansive and infiltrative
- Mechanisms and pathways of metastasis of atypical cells
- International TNM Classification of Malignant Tumors
- Effect of polycyclic aromatic hydrocarbons on the cell cycle
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