Differentiation and cellular atypia
Benign neoplasms retain a high degree of differentiation, whereas malignant ones demonstrate a wide spectrum ranging from well-differentiated to completely undifferentiated. Complete loss of similarity to mature tissue is called anaplasia. According to modern concepts, carcinomas develop not as a result of dedifferentiation of mature elements, but initially form from undifferentiated cells possessing stem cell properties.
Cellular atypia affects all cell components, but is most prominent in the nucleus. Nuclei enlarge drastically (due to polyploidy, endomitosis, and impaired DNA endoreduplication), and their contours become jagged. Chromatin is distributed chaotically, condensing into clumps beneath the nuclear envelope. The proportion of inactive DNA (heterochromatin) increases, indicating functional primitivism. Viral particles, tubular structures, and nuclear membrane pockets may be found inside the nucleus.
Ultrastructural changes and mitoses
Electron microscopy reveals profound alterations in organelles, forming ultrastructural atypia:
- Nucleoli and membrane: The number of nucleoli increases, they enlarge and do not disappear during division (they persist). The number of pores in the nuclear membrane decreases, impairing transport between the nucleus and the cytoplasm.
- Mitochondria: Due to the shift to anaerobic glycolysis, their number typically decreases (exceptions are onocytomas and granular cell renal cell carcinomas). Giant forms with altered orientation of cristae appear.
- Cytoskeleton: Microtubules and microfilaments are arranged chaotically. This disrupts the function of adhesion molecules (integrins, cadherins), which drives invasive growth and metastasis.
- Surface: The cell membrane forms folds and microvilli, where receptors for carcinogens concentrate.
Mitotic activity is of particular diagnostic significance. In undifferentiated tumors, it is extremely high. However, mitosis alone does not indicate malignancy. The true criterion is atypical mitotic figures: tripolar and tetrapolar, as well as multipolar mitotic spindles.
Biochemical and antigenic atypia
Tumor cells alter their metabolism to survive under hypoxic conditions. This biochemical (histochemical) atypia is manifested by the enhanced synthesis of oncoproteins, growth factors, and embryonic receptors. Simultaneously, the levels of histones and cyclic adenosine monophosphate (cAMP) drop.
Antigenic atypia involves the restructuring of the immune profile. The tumor loses normal tissue-specific antigens and histocompatibility antigens, which helps it establish the body's tolerance and evade the immune response. In return, tumor-specific and oncofetal antigens appear.
Proof of their existence comes from experiments involving graft rejection in inbred mice and the detection of cytotoxic T-lymphocytes in tumor infiltrates (e.g., in human melanomas). Specific antigens have been identified in neuroblastoma, Burkitt lymphoma, and osteosarcoma. Their identification by immunohistochemical methods is critical for accurate diagnosis.
Functional atypia and stromal changes
Alteration of cellular specialization leads to functional atypia. The cell loses its original tasks and may acquire entirely new ones. A striking example: in poorly differentiated scirrhous gastric cancer, cells stop producing mucus and actively synthesize collagen for the tumor stroma.
The stroma in rapidly growing anaplastic tumors is often sparse and fails to keep pace with parenchymal growth. Due to insufficient blood supply, extensive areas of ischemic necrosis form in the center of such neoplasms. Additionally, the tissue may contain tumor giant cells with multiple hyperchromatic nuclei, which must be differentiated from foreign body macrophage giant cells and Pirogov-Langhans cells during differential diagnosis.
Briefly: answers to topical questions
How does tissue atypia differ from cellular atypia?
Tissue atypia consists of the disruption of tissue architecture, whereas cellular atypia manifests as changes at the level of the cells themselves and their nuclei.
| Characteristic | Tissue atypia | Cellular atypia |
|---|---|---|
| Core of changes | Disruption of the stroma-to-parenchyma ratio, vascular angioarchitecture, appearance of bizarre formations | Anaplasia, cataplasia, dysdifferentiation, cellular and nuclear polymorphism, nuclear hyperchromasia |
| Occurrence | Characteristic of both benign and malignant neoplasms | A distinguishing feature exclusively of malignant tumors |
Which specific oncofetal antigens are used in clinical diagnostics?
The provided sources specifically name the following carcinoembryonic / oncofetal antigen used as a diagnostic marker:
- Carcinoembryonic antigen (CEA) — specified as an organ-specific marker of carcinomas, particularly in bowel cancer.
Also, in the sources, alpha-fetoprotein is cited as an example of a carcinoembryonic antigen, although its specific clinical and diagnostic application is not detailed in these sources.
What morphological features characterize tissue atypia?
Morphological features of tissue atypia are expressed as the disruption of tissue architecture and include the following changes:
- Ratio disruption — altered proportions between the tumor parenchyma and stroma (e.g., sparse stroma or its pronounced proliferation).
- Structural alteration — violation of the size and shape of tissue elements (glands become irregular in shape, of varying caliber, and branching).
- Appearance of formations — formation of bizarre tissue structures of various sizes, loss of their proper angioarchitecture.
- Absence of structures — complete absence of organized architectural areas in diffuse or signet-ring cell growth types.
What histological grades of malignancy (Grade) exist for tumors?
Histological grades of malignancy (Grade) reflect the level of tumor differentiation and include the following main gradations:
- Grade Gx — differentiation grade cannot be assessed.
- Grade G1 — well-differentiated tumor.
- Grade G2 — moderately differentiated tumor.
- Grade G3 — poorly differentiated tumor.
- Grade G4 — undifferentiated tumor.
For primary central nervous system tumors, 4 grades (Grade 1–4) are distinguished based on the presence of nuclear atypia, mitoses, endothelial proliferation, and necrosis. For urinary bladder cancer, low-grade (Low grade) and high-grade (High grade) carcinomas are distinguished.
To remember the essence of antigenic atypia, use the rule "Minus old, plus new": the cell loses normal (histocompatibility) antigens and acquires new ones (oncofetal).
Class and exam questions
What is the main morphological criterion of malignancy?
The presence of atypical (bizarre) mitotic figures, such as multipolar division spindles. Normal mitoses can also occur in benign processes or productive inflammation.
Why is the number of mitochondria reduced in tumor cells?
This is due to altered energy metabolism—a shift of cells to anaerobic glycolysis to survive under hypoxic conditions. Onocytomas are an exception.
How does cytoskeleton remodeling affect tumor behavior?
The chaotic arrangement of microtubules and microfilaments disrupts the function of adhesion molecules (integrins). Cells lose contact with the extracellular matrix, which drives invasive growth and metastasis.
Where do carcinomas originate according to current theory?
They develop not as a result of dedifferentiation (loss of maturity) of normal cells, but initially arise from completely undifferentiated elements with stem cell properties.
What else to study on this topic
- Mechanisms of tumor giant cell formation
- Immunohistochemical diagnosis of specific antigens
- Differences between Pirogov-Langhans cells and tumor giant cells
- The Role of Integrins and Cadherins in Metastasis
- Intranuclear Inclusions in Virus-Associated Tumors
Master the entire topic in the "Pathological Anatomy" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on «Tumor Atypia» and 4,414 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 153 video lessons on the subject
Other topics in the section "Tumor Growth"
Free video lessons: pathological anatomyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.