Types of tumor cell atypia
Atypia is a general characteristic of a transformed cell, manifesting at several levels: growth, metabolism, function, and structure. Growth atypia consists in altered division kinetics: while in normal epithelial tissue the proportion of dividing cells is about 5%, in a tumor of epithelial origin it reaches 60–80%. Concurrently, cell maturation is impaired (anaplasia).
The key manifestations of growth atypia include three interrelated phenomena: invasive growth, metastasis, and recurrence. Structural atypia is considered at the cellular and tissue levels.
Invasive growth
Invasive growth is the infiltration of surrounding tissues by tumor cells. The main mechanism is a decrease in cell adhesion strength. It is caused by:
- deficiency of adhesion molecules in the intercellular matrix or their enhanced hydrolysis;
- increased negative charge of the tumor cell surface due to the binding of negatively charged radicals and decreased cation content, leading to electrostatic repulsion;
- emergence of the capacity for amoeboid movement due to changes in the physicochemical properties of the cytolemma and reduced surface tension;
- overexpression of receptors for interstitial adhesion molecules;
- loss of contact inhibition, production of growth stimulation factors, and the presence of onco-chemoattractants.
Metastasis
Metastasis is the transport of tumor cells away from the primary (parent) node with the formation of a secondary tumor of the same histological structure, usually in another organ. The routes of metastasis include:
- lymphogenic — characteristic of carcinomas;
- hematogenous — characteristic of sarcomas;
- tissue (implantation) — for example, upon contact of gastric cancer cells with the peritoneum.
Stages of lymphogenic and hematogenous metastasis:
- Detachment of the cell from the primary tumor and invasion of the vessel wall.
- Circulation in the blood or lymphatic stream; shielding of tumor cell antigens by fibrin, platelets, and leukocytes with the formation of a microthrombus — the embolism stage.
- Invasion of the embolus through the vessel wall into the tissue and formation of a secondary focus.
Metastases are characterized by organ selectivity (tropism): for example, lung cancer frequently metastasizes to bones. Tropism is determined by the metabolic specificity of the target organ, blood supply features, low efficiency of local anti-tumor resistance, and the presence of onco-chemoattractants.
Recurrence
A tumor recurrence is the re-emergence of a neoplasm of the same histological structure at the original site after its removal or destruction. Main causes:
- incomplete removal of tumor tissue during surgery;
- capture by normal cells in the growth zone of DNA fragments released from blastoma cells destroyed during surgery or radiation/chemotherapy.
Metabolic and functional atypia
The tumor acts as a metabolic trap: it intensively absorbs amino acids, lipids, carbohydrates, and ions, ensuring the predominance of anabolic processes. Characteristic shifts include:
- enhanced synthesis of nucleic acids and plastic metabolism;
- increased glucose utilization;
- loss of cellular specialization with cessation of normal metabolic enzyme synthesis (e.g., glycerophosphate dehydrogenase);
- dominance of anaerobic glycolysis as the pathway for ATP synthesis — proliferation outpaces vascular growth, leading to metabolic acidosis;
- decreased efficiency of local feedback metabolic regulation and transition to archaic auto- and paracrine mechanisms;
- escape of cells from homeostatic control systems.
Functional atypia manifests as hypofunction, hyperfunction (e.g., hyperinsulinism in insulinoma, hormone excess in thyroid or adrenal cortex tumors), and dysfunction — the synthesis of proteins uncharacteristic of cells of this tissue (e.g., collagen production by lung cancer cells leading to sclerosis).
Tumor progression
Tumor progression is the regular alteration of tumor properties after its inception. Changes affect biochemical, morphological, and functional characteristics and occur independently of each other in different cell clones. As a result, a single tumor contains heterogeneous clones with a diverse set of properties.
High variability increases tissue adaptability: different clones survive under conditions of varying oxygenation, nutrition, and immune pressure. Simultaneously, continuous phenotype shifting is accompanied by the appearance of new antigens, leading to overload of the immune system and the development of immunodeficiency, increasing the tumor's resistance to therapy.
Anti-tumor resistance
Anti-tumor resistance is the aggregate of mechanisms that prevent the emergence, progression, and spread of a tumor. Three groups of factors are distinguished:
- Anti-carcinogenic — prevent the penetration and action of carcinogens;
- Anti-mutational — detect and eliminate oncogenes, suppress their expression (e.g., the p53 protein, which arrests the cell cycle and triggers apoptosis via p21);
- Anti-cellular — destroy tumor cells and inhibit their growth.
Anticellular mechanisms are divided into non-immune (phagocytes, NK cells, tumor necrosis factor α) and immune mechanisms, mediated by cytotoxic T-lymphocytes and specific antibodies. When defense is preserved, a latent form of cancer is possible: the tumor exists but does not progress, invade, or metastasize. When immunodeficiency develops, the latent process transitions into an active form with a typical clinical presentation.
Key points
- Tumor cell atypia affects growth, metabolism, function, and structure.
- Invasive growth is primarily caused by reduced intercellular adhesion and the appearance of amoeboid motility.
- Metastasis proceeds via lymphogenic, hematogenous, and tissue routes, passing through stages of invasion, embolism, and secondary node formation.
- Metastases exhibit organ tropism, determined by the metabolism and blood supply of the target organ.
- Recurrence occurs due to incomplete tumor removal or uptake of its DNA by normal cells.
- The tumor operates as a metabolic trap with a predominance of anaerobic glycolysis and the development of acidosis.
- Tumor progression generates heterogeneous clones and promotes resistance and immunodeficiency.
- Anti-tumor resistance includes anti-carcinogenic, anti-mutational, and anti-cellular mechanisms; its weakening turns latent cancer into an active form.