Theories of transformation and cancer stem cells
Modern pathologic anatomy views the development of neoplasms as a process originating from tissue stem or, in some cases, progenitor cells. A major paradox of oncogenesis is the combination of initial monoclonal origin and resulting pronounced heterogeneity.
- Clonality: It has been proven that any tumor is initially formed as a result of the transformation and subsequent growth of a single cell. This means that the entire tumor mass is an expanded clone.
- Heterogeneity: Despite originating from a single starting cell, a clinically detectable neoplasm always contains a highly diverse population of cells.
- Cancer stem cells: According to the prevailing hypothesis, within the established tumor clone (by analogy with normal tissues) there is a specific subpopulation of cells possessing stem cell properties. It is these cells that maintain the continuous growth and renewal of the neoplastic tissue.
Morphological manifestations of dysplasia
Dysplasia represents a key stage of morphogenesis in which the normal tissue structure is disrupted. Changes affect both the parenchyma (epithelium) and the stroma, although the overall tissue architecture is still preserved at this stage.
Changes in the epithelial layer:
- Cellular polymorphism: Epithelial cells lose uniformity in shape and size, becoming polymorphic.
- Nuclear anomalies: Cell nuclei become hyperchromatic (intensely stained).
- Shift in mitotic activity: Mitotic figures are detected not only in the usual basal compartments of the epithelium but also shift into the overlying layers.
- Basement membrane response: It thickens due to the excessive accumulation of certain types of collagens.
Changes in the stroma and microenvironment:
- The composition of the extracellular matrix changes qualitatively.
- A pronounced fibroblastic reaction develops.
- Cellular infiltrates form in the surrounding tissues (specifically, lymphoid infiltrates appear), reflecting a local response to the process.
Intraepithelial neoplasia and background processes
Intraepithelial neoplasia is a condition in which true tumor cells are already present in foci of dysplasia, while the basement membrane remains intact.
Depending on the severity of cellular atypia and the number of mitoses observed in the tissue, 3 grades of intraepithelial neoplasia are distinguished. In addition to stereotyped manifestations, dysplasia in various organs has its own specific features. In hematology, an analog of a pre-tumor state (pre-leukemia) is considered to be an increase in the relative content of blast cells up to 9%.
Factors and background for the development of dysplasia:
- On the background of hyperplasia (most commonly): Dysplasia forms under conditions of active cell proliferation accompanying chronic inflammation and dysregeneration.
- On the background of atrophy (less commonly): Occurs in pathologies such as liver cirrhosis (LC) or atrophic gastritis with epithelial remodeling.
The mechanism combining atrophy and dysplasia is explained by common genetic mechanisms. In particular, the activation of cellular oncogenes and mutations in the p53 suppressor gene can lead to diametrically opposite results: either induce apoptosis and atrophy, or trigger proliferation (with or without dysplasia).
Molecular genetic diagnostics
Morphological changes are always preceded by profound molecular alterations. Already at the dysplasia stage, the functioning of key molecules in cells changes cardinally:
- Oncoproteins and growth factors.
- Integrins and adhesion molecules.
Methods of molecular biology and immunohistochemistry (IHC) are used to detect these hidden genetic defects.
Clinical significance: Genetic alterations can precede classical morphological changes. This allows the use of molecular markers for the early diagnosis of pre-tumor processes, when visual signs are not yet sufficient to make a diagnosis.
Briefly: answers to topical questions
What mechanisms explain the formation of tumor heterogeneity despite its initial monoclonality?
The formation of tumor heterogeneity despite its initial monoclonal origin is explained by the theory of clonal evolution and the accumulation of genetic defects.
Mechanisms include:
- Genetic instability — a high frequency of random mutations and the appearance of additional chromosomal abnormalities in the stem cells of the clone.
- Clonal evolution — constant variability in cell properties, leading to phenotypic evolution and autonomy.
- Clonal selection — the selection of cell clones best adapted for survival as the disease progresses.
As a result, the formed tumor represents a combination of various cell subpopulations arising from a single transformed cell.
How do mild, moderate, and severe dysplasia of stratified squamous epithelium differ morphologically?
The morphological differences in the grades of stratified squamous epithelium dysplasia are determined by the severity of cellular atypia, the proportion of the thickness of the epithelial layer affected, and the number of mitoses.
| Grade of dysplasia | Morphological characteristic |
|---|---|
| Mild dysplasia | Atypia is limited to the lower third of the epithelial layer |
| Moderate dysplasia | More pronounced atypia and spread of changes in the epithelial layer compared to mild dysplasia |
| Severe dysplasia | Corresponds to high-grade intraepithelial neoplasia and carcinoma in situ |
Intraepithelial neoplasia is characterized by structural and cellular atypia, impaired differentiation, and altered epithelial stratification with an intact basement membrane.
What is the role of p53 suppressor gene mutations in tumor morphogenesis?
The role of p53 suppressor gene mutations in tumor morphogenesis consists of the loss of cell cycle control and the blockage of apoptosis.
Normally, the p53 protein halts the cell cycle for DNA repair or triggers apoptosis. Upon mutation:
- Mutant p53 acts as a cellular oncogene (dominant trait).
- Conformational changes of the protein occur along with its accumulation in cell nuclei.
- Apoptosis is not triggered, allowing cells with damaged DNA to survive.
- Active proliferation of mutant cells is stimulated.
This leads to the formation of an unstable genome, the accumulation of additional mutations and translocations, culminating in malignant transformation and the development of tumor resistance.
To memorize the epithelial changes in dysplasia, use the rule "PNMA": Polymorphism of cells, Nuclei (hyperchromatic), Mitoses (above the basal layer), Activated basement membrane (thickened).
Class and exam questions
From which cells does a tumor initially develop?
It is believed that the source is tissue stem or progenitor cells. They give rise to a clone within which cancer stem cells are present.
How does intraepithelial neoplasia differ from invasive cancer?
The main criterion is the presence of tumor cells with a fully intact basement membrane in foci of dysplasia.
Can dysplasia develop against the background of atrophy?
Yes, although this occurs less frequently than in hyperplasia. Examples include atrophic gastritis or liver cirrhosis. This is based on common genetic mechanisms, including mutations in the p53 gene.
What else to study on this topic
- Specific morphological features of dysplasia in various organs
- The role of the p53 tumor suppressor gene in the balance between apoptosis and proliferation
- Mechanisms of extracellular matrix alterations during the fibroblastic reaction
- Immunohistochemistry (IHC) as a method for detecting early oncoproteins
- Heterogeneity of the tumor population in monoclonal origin
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