Malignancy is the process of transformation of benign cells into malignant ones. It can occur in any normal tissues or tissues of benign tumors. It is accompanied by a decrease in the level of differentiation, a change in morphological properties, impaired function and rapid cell proliferation, progressive growth of neoplasms and the development of distant metastases. Malignancy is confirmed on the basis of clinical data, results of laboratory and instrumental studies. In the process of tumor treatment, surgical interventions, chemotherapy and radiotherapy are usually used. It is possible to use hormones, immunostimulants and other drugs.
Malignancy (malignancy, malignant degeneration) is a complex pathomorphological process during which benign cells acquire the properties of malignant ones. Malignancy can be subjected to both normal cells and already altered, but showing no signs of malignancy. Most often, foci of malignancy occur in the area of ulcers, polyps and various benign tumors. The cause of malignancy may be a genetic predisposition and harmful environmental factors.
At the initial stages, malignancy is asymptomatic, therefore, early diagnosis of malignant neoplasms is associated with significant difficulties, however, regular preventive examinations, the use of modern laboratory and instrumental research methods can partially solve the problem of early detection of malignancy. Diagnostics and treatment are carried out by specialists in the field of oncology, gastroenterology, pulmonology, neurology, dermatology, otolaryngology, gynecology, orthopedics and doctors of other specialties (depending on the localization of the tumor).
Currently, malignant tumors are the second most common cause of death after cardiovascular diseases. In 2012, more than 8 million people died of cancer. The probability of malignancy increases with age, however, along with elderly people, malignant tumors often affect children and patients of working age. The most common types of cancer are lung cancer, stomach cancer, breast cancer, liver cancer and colon cancer.
As a result of malignancy, approximately 150 types of malignant cells can form in the human body. About 80% of these cells are of epithelial origin, 15% are connective tissue, 5% are hematogenic. According to experts, the prevalence of malignancy in the coming decades will grow, which is due to a number of factors, including an increase in life expectancy, unfavorable environmental conditions, bad habits, the use of a large number of chemicals, an increase in the level of ionizing radiation, etc. All this makes it extremely important to study the processes of malignancy, as well as to develop optimal algorithms for detecting such processes during mass examinations, diagnosis and treatment of non-oncological diseases.
The cause of cell malignancy is a combination of several factors, among which experts indicate chemical carcinogens, environmental features, some viruses, hormonal imbalance conditions, age, bad habits and unfavorable heredity. During the research, it was found that more than 2000 different chemicals can provoke malignancy, but the degree of their influence on the processes of malignant cell degeneration can vary greatly.
The list of chemical compounds that certainly cause cell malignancy includes polycyclic aromatic hydrocarbons (sources are transport, industrial enterprises and heating systems), nitrosamines (found in cigarettes, some beers and amidopyrine), hydrazine derivatives (included in herbicides and some medicines), asbestos and other mineral fibers (source are industrial productions), as well as some metal compounds.
The most significant physical factor of malignancy is solar radiation, the level of which directly affects the likelihood of developing skin cancer. The lighter the skin and hair and the longer a person is exposed to sunlight, the higher the risk of developing melanoma, basal cell carcinoma and squamous cell skin cancer. In addition, malignancy can be stimulated by ionizing radiation, provoking the occurrence of leukemia, bone tumors (radioactive strontium) and thyroid cancer (radioactive cesium and iodine).
It has been proven that the probability of malignancy increases when certain viruses are exposed to cells, in particular, the ATLV virus (causes leukemia), Epstein–Barr virus (provokes the development of Burkitt lymphoma), human papillomavirus (plays a role in the occurrence of cervical cancer) and herpes virus type II. Malignancy is also promoted by hormonal imbalance. Hormones can directly provoke malignancy, act indirectly on cells, stimulating their proliferation, have a negative effect on immunity and alter the metabolism of some carcinogens.
A significant role in the process of malignancy is played by genetic predisposition. Many hereditary diseases with a high probability of malignancy have been described, for example, systemic intestinal polyposis, in which most patients develop colon cancer by the age of 40-50, or Down’s disease, in which the risk of developing leukemia is 11 times higher than the population average. There is a connection between malignancy and congenital malformations.
The dependence between the probability of malignancy of tissues of certain organs and the sex of the patient is revealed. Men are 2.4 times more likely to suffer from eye tumors, 2.1 times more likely to have stomach neoplasms, 2 times more likely to have malignant lesions of the nasopharynx, 1.7 times more likely to have bone tumors. In women, malignancy of thyroid tissue is twice as often detected. The first place in prevalence in men is occupied by tumors of the respiratory tract, in women – tumors of the genitals and breast. In most cases, the probability of malignancy in patients of both sexes increases with age, but some types of neoplasms are more often detected in children or young people.
The habits that have the strongest effect on cell malignancy include smoking, poor nutrition and alcohol intake. In smokers, lung cancer develops 11 times more often; tumors of the oral cavity, larynx and pharynx – 7 times more often; neoplasms of the bladder – 2.2 times more often; pancreatic tumors – 1.7 times more often than in non-smokers. The main eating habits that increase the likelihood of malignancy are the intake of large amounts of meat, fatty, spicy and spicy foods, a tendency to over-salting and the use of insufficient amounts of vegetable fiber. Alcohol itself does not cause malignancy, but acts as an activator, increasing the impact of other factors.
The initial stage of malignancy is initiation – mutation of cells under the influence of internal or external harmful factors. Cellular or viral oncogenes appear in the cell genome – altered genes that cause the growth and reproduction of defective cells. Defective cells are constantly formed in the human body, but normally the process of malignancy is interrupted at the initiation stage, since such cells undergo apoptosis – a regulated process of cell death. With simultaneous shutdown of genes that cause apoptosis and activation of genes that prevent apoptosis, defective cells do not die, but continue to develop.
With repeated exposure to the cells of the same or another harmful factor, the second stage of malignancy occurs – promotion. Oncogenes are activated, stimulating the proliferation of defective cells. However, even this is not enough for the development of a malignant tumor. The growth of the neoplasm becomes possible only after passing the third stage of malignancy – the avoidance of defective cells from the differentiation process. Evasion usually occurs under the influence of certain microRNAs.
In addition, the transition to the third stage of malignancy may be due to a lack of cytokinins that contribute to the transition of the cell to a higher level of differentiation. Over time, the number of low-differentiated cells increases, and a microscopic area of altered tissue appears. Cells with a predominant set of chromosomes form the so–called stem line – the basis of the tumor. One of the features of malignancy is the genetic instability of cells, due to which the cellular composition of the neoplasm is constantly changing, instead of one stem line, others appear.
Altered cells that have lost the ability to respond to external influences (the influence of the microenvironment, immune surveillance) continue to actively divide. The fourth stage of the development of a malignant neoplasm is coming – tumor progression. The tissue that has changed in the process of malignancy sprouts neighboring organs, destroys the walls of blood and lymphatic vessels. Neoplasm cells enter the blood and lymph, and then spread throughout the body, “settling” in the lymph nodes and distant organs. From the “settled” cells, new foci of tumor growth are formed – secondary neoplasms (metastases).
From the point of view of tissue properties, the following stages of malignancy can be distinguished: tissue hyperplasia, the appearance of areas of focal proliferation, the appearance of a benign tumor, the formation of areas of dysplasia, cancer in situ (a malignant tumor that does not germinate surrounding tissues), invasive malignant neoplasm. In some cases, the stage of a benign tumor may be absent. The stages of focal proliferation, benign tumor and dysplasia are considered as precancerous conditions.
Properties of the tumor after malignancy
Malignant neoplasms have a number of properties that are absent in any normal cells and tissues of the body:
- As a result of malignancy, the tumor becomes capable of rapid growth, accompanied by compression or destruction of surrounding tissues.
- With malignancy, the neoplasm has the ability to infiltrate (embed) into the surrounding tissues.
- After malignancy, the tumor has the ability to spread by metastasis. Malignant neoplasm cells migrate with the blood and lymph flow, and then “settle” in various organs and tissues, giving rise to secondary tumors (metastases). It has been established that there is a certain “tropicity” – a tendency to metastasis to certain organs and tissues, depending on the type of primary neoplasm.
- With malignancy, the tumor has the ability to produce toxins that have a pronounced negative effect on the patient’s body. The development of a malignant neoplasm is accompanied by general intoxication, fatigue, decreased appetite and weight loss up to cachexia.
- After malignancy, the altered cells are beyond the control of the body’s immune system.
- Malignancy is associated with a high tendency to mutations, as a result of which cells acquire unusual abilities (the ability to uncontrolled growth, lack of response to immune effects, metastasis, etc.).
- Malignancy is characterized by a low level of cell differentiation. The lower the level of cell maturity, the more malignant the tumor, the faster it progresses and gives metastases, the higher its resistance to chemotherapy and radiotherapy.
- Malignant neoplasm has a pronounced cellular and tissue atypism.
- In the process of malignancy, altered cells and tissues have the ability to stimulate the growth of blood vessels. The tissue of a malignant tumor is well vascularized, hemorrhages often occur in it.