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Morphology of Tumor Growth

Morphologia incrementi tumoris

For medical students2 min readUpdated 2026-10-10

Tumor growth is a pathological process characterized by unregulated and autonomous cell proliferation. Malignancy is fundamentally driven by a high differentiation block in cells originating from pluripotent elements.

Parenchyma and StromaThe primary structural components of any tumor.
Differentiation BlockThe higher the block, the less differentiated the tumor.
IntegrinsMediate cell-cell adhesion and signal transduction to the nucleus.
AngiogenesisTumor growth depends on the development of a vascular network.

Differentiation and Malignancy

Malignant neoplasms originate from pluripotent cells and exhibit a pronounced differentiation block. There is a fundamental rule: the greater the degree of malignant transformation and the deeper the differentiation block, the lower the differentiation grade 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 tumor cell behavior:

This interaction is mediated via integrins located on the membranes of tumor cells. They are responsible for intercellular contacts and connection with the stromal matrix, transmitting signals to the cytoskeleton and subsequently into the cell nucleus. Furthermore, the composition of the stroma has diagnostic significance: for instance, the presence of type IV collagen is important for the differential diagnosis of sarcomas.

Angiogenesis and Tumor Vessel Characteristics

The development of a neoplasm directly depends on the status of its vascular network. Angiogenesis is stimulated by specific factors (angiogenin, angiopoietins, fibroblast growth factors) and extracellular matrix components.

Tumor vessels are formed under the influence of aberrant mitogenetic stimulation, resulting in defective capillary vessels. The walls of such vessels are altered: the endothelium may be entirely absent or replaced by tumor cells.

Pattern of Tumor Growth

The primary property of a tumor is autonomous (uncontrolled) growth. Depending on the number of primary foci, the following are distinguished:

  1. Unicentric growth — development of a tumor from a single focus as a solitary nodule.
  2. Multicentric growth — simultaneous emergence of tumor foci in several different tissue sites.

Mnemonic

UM in the stroma: Unicentric and Multicentric growth refer to the number of nodes, while integration via integrins relays signals to the nucleus.

Frequently asked questions

What types of tumor growth exist in relation to surrounding tissues?

Relative to surrounding tissues, there are two primary types of tumor growth.

  • Expansive growth — the tumor grows "within itself," displacing adjacent tissues and forming a connective tissue capsule (pseudocapsule). This type of growth is characteristic of benign tumors.
  • Infiltrative (invasive) growth — characterized by extension into adjacent tissues and destruction of surrounding structures. It is typical for malignant neoplasms.

Apositional growth is also noted in classical classifications.

What types of tumor growth are distinguished in relation to the lumen of a hollow organ?

Relative to the lumen of a hollow organ, two types of tumor growth are distinguished.

  • Exophytic growth — characterized by tumor growth into the lumen of a hollow organ, filling its cavity.
  • Endophytic growth — represents tumor growth into the organ wall, infiltrating the wall layers.
How does tissue atypia manifest morphologically?

Morphologically, tissue atypia manifests as a disruption of tissue architecture, which ceases to resemble the structure of the mature parent tissue. Key manifestations include:

  • Ratio alteration — imbalance between the tumor parenchyma and stroma (e.g., a sharp shift toward sparse or abundant stroma).
  • Structural modification — changes in the size and shape of tissue elements (glands may become irregular in shape and caliber).
  • Bizarre formations — appearance of atypical tissue structures of varying sizes that lose proper angioarchitecture and orderly orientation.
How does cellular atypia manifest morphologically?

Morphologically, cellular atypia is manifested by pronounced alterations in cell structure, nuclei, and mitotic activity.

  • Cellular polymorphism — marked variability in cell shape and size, the appearance of giant, small primitive, and multinucleated cells.
  • Nuclear atypia — hyperchromasia, polyploidy, increased nuclear-cytoplasmic ratio, irregular nuclear contours, and prominent nucleoli.
  • Mitotic alterations — increased overall number of mitotic figures and the presence of atypical mitotic figures.
  • Disorganized architecture — loss of normal cell polarity and disorganized growth of cell clusters.
What is the relationship between tumor differentiation and malignancy?

Malignant tumors originate from pluripotent cells and possess a high differentiation block. The higher the level of malignancy and differentiation block, the less differentiated the tumor is.

What role do integrins play in the tumor process?

Integrins are located on tumor cell membranes and mediate interactions between cells and with the stromal matrix. They transmit signals from the cytoskeletal elements to the nucleus, determining the tumor's capacity for invasion and metastasis.

What are the structural features of tumor blood vessels?

Tumor vessels are defective (predominantly capillary-type) due to aberrant mitogenetic stimulation. Their endothelium may be replaced by tumor cells or absent entirely.

What types of tumor growth are distinguished based on the number of nodules?

Unicentric growth (originating from a single site as one nodule) and multicentric growth (simultaneous emergence in multiple tissue sites).

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