Differentiation and malignancy
Malignant neoplasms originate from pluripotent cells and are characterized by a pronounced differentiation block. There is a fundamental rule: the higher the level of malignancy and the deeper the differentiation block, the lower the degree of differentiation of the tumor itself.
Tumor stroma and its modifying influence
Any neoplasm consists of parenchyma and stroma. The role of the stroma is not limited to trophic and supportive functions—it actively influences the behavior of tumor cells:
- Regulates proliferation and differentiation.
- Determines the propensity for invasive growth and metastasis.
Interaction is carried out through integrins located on the membranes of tumor cells. They are responsible for intercellular contacts and connection with the stroma matrix, transmitting a signal to the cytoskeleton and further into the cell nucleus. In addition, the composition of the stroma has diagnostic significance: for example, the presence of type IV collagen is important for the differential diagnosis of sarcomas.
Angiogenesis and features of tumor vessels
The development of a neoplasm directly depends on the state of the vascular network. Angiogenesis is stimulated by special factors (angiogenin, angiopoietins, fibroblast growth factors) and components of the extracellular matrix.
Tumor vessels are formed under the influence of aberrant mitogenetic stimulation, which leads to the appearance of defective capillary vessels. The walls of such vessels are altered: the endothelium may be completely absent or replaced by tumor cells.
Nature of tumor growth
The main property of a tumor, according to the classical definition by A.I. Strukov and V.V. Serov (1995), is autonomous (uncontrolled) growth. Depending on the number of primary nodes, the following are distinguished:
- Unicentric growth — development of a tumor from a single focus as a single node.
- Multicentric growth — simultaneous appearance of tumor foci in several different areas of tissue.
Briefly: answers to topical questions
What types of tumor growth exist in relation to surrounding tissues?
In relation to surrounding tissues, two main types of tumor growth are distinguished.
- Expansive growth — the tumor grows "within itself", pushes aside adjacent tissues and forms a connective tissue capsule (pseudocapsule). This type of growth is characteristic of benign tumors.
- Infiltrating growth (invasive) — characterized by sprouting into adjacent tissues and destruction of surrounding structures. It is typical for malignant neoplasms.
Appositional growth is also mentioned in the classification.
What types of tumor growth are distinguished in relation to the lumen of a hollow organ?
In relation to the lumen of a hollow organ, two types of tumor growth are distinguished.
- Exophytic growth — characterized by the growth of the neoplasm into the lumen of a hollow organ, in which the tumor fills its cavity.
- Endophytic growth — represents the growth of the tumor into the organ wall, in which it infiltrates this wall.
How is tissue atypia of a tumor manifested morphologically?
Morphologically, tissue atypia is manifested by a violation of the tissue structure, which ceases to repeat the structure of the mature source tissue. The main manifestations include:
- Ratio disturbance — imbalance between the parenchyma and stroma of the tumor (for example, a sharp shift towards scanty or abundant stroma).
- Structural alteration — a change in the size and shape of tissue elements (glands can become irregular in shape, of various calibers).
- Bizarre formations — the appearance of atypical tissue structures of various sizes that lose correct architectonics and ordered orientation.
How is cellular atypia of a tumor manifested morphologically?
Morphologically, cellular atypia is manifested by pronounced changes in the structure of cells, their nuclei, and mitotic activity.
- Cellular polymorphism — pronounced variability of cells in shape and size, the appearance of giant, small primitive, and multinucleated cells.
- Nuclear atypia — hyperchromasia, polyploidy, increased nuclear-cytoplasmic ratio, jagged nuclear contours, and the appearance of large nucleoli.
- Mitotic alteration — an increase in the total number of mitotic figures and the appearance of abnormal mitotic figures.
- Organizational disruption — loss of normal cell polarity and disorganized growth of complexes.
UMka in the stroma: Unicentric and Multicentric growth refer to the number of nodes, and integration through integrins directs the signal to the nucleus.
Class and exam questions
What is the relationship between tumor differentiation and malignancy?
Malignant tumors originate from pluripotent cells and have a high differentiation block. The higher the level of malignancy and differentiation block, the less differentiated the tumor turns out to be.
What role do integrins play in the tumor process?
Integrins are located on the membranes of tumor cells and ensure their interaction with each other and with the stroma matrix. They transmit a signal from the cytoskeleton elements to the nucleus, determining the tumor's ability to invade and metastasize.
What are the structural features of tumor vessels?
Tumor vessels are defective (predominantly capillary type) due to aberrant mitogenetic stimulation. Their endothelium can be replaced by tumor cells or absent altogether.
What types of tumor growth are distinguished by the number of nodes?
Unicentric growth (from a single site as a single node) and multicentric growth (simultaneous emergence in several tissue areas) are distinguished.
What else to study on this topic
- Origin of tumor stroma cell elements
- The role of basement membrane components (laminin, fibronectin, type IV collagen)
- The action of angiogenic fibroblast growth factors and angiopoietins
- Mechanisms of signal transduction from integrins to the tumor cell cytoskeleton
- Differential diagnosis of sarcomas by stroma composition
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