Tumor cytogenetics

Foundation of tumor diagnostics and classification

The modern approach to systematizing oncological diseases relies on a comprehensive assessment of affected tissues. The fundamental classification of tumor processes distinguishes three key groups of manifestations. First, the clinical characteristics of the disease course are taken into account. Second, the molecular genetic features of the tissues are analyzed. Third, morphological signs are evaluated. It is the morphological picture that is fundamental: on its basis, the attending physician establishes the final diagnosis, develops an optimal therapy regimen, and formulates a prognosis for a specific clinical case.

For a comprehensive study of cells, specialists have a wide range of laboratory techniques at their disposal. The main tools include polymerase chain reaction (PCR), in situ hybridization technology, various blot analysis formats, and classical cytogenetic profiling. In addition, immunohistochemistry (IHC) and electron microscopy (EM) are routinely used. If the doctor faces the task of tracking the patient's condition dynamics and confirming remission, flow cytometry is the method of choice.

Systematization of tumor markers

Tumor markers are specific molecular indicators that allow for the detailing of the biological potential of a neoplasm. They are generally divided into several major categories reflecting different stages of carcinogenesis:

• Indicators of cellular differentiation.
• Histogenetic and cytogenetic parameters.
• Markers indicating the presence of chromosomal aberrations and structural gene rearrangements.
• Indices of impaired cellular proliferation capacity.
• Indicators of programmed cell death (apoptosis).
• Markers demonstrating the tumor's potential for invasive growth and metastasis.

In oncological practice, molecular molecules responsible for specific cellular mechanisms are detailed. E-cadherin and CD24 proteins are responsible for intercellular adhesion processes. The level of cell differentiation is assessed by the expression of the human epidermal growth factor receptor HER-2. The formation of new blood vessels (angiogenesis) is controlled by hypoxia-inducible factor 1α (HIF-1α) and metalloproteinase enzymes. The capacity of tissues for active division is recorded using the Ki-67 antigen, and mitosis processes using the Aurora A marker. The mechanisms of apoptosis suppression are regulated by Bcl-2 proteins and survivin. Also, objects of close study are the C-met protein (MET), epithelial-mesenchymal transition phenomena, and morphological signs of vascular invasion.

Risk stratification and clinical limitations

Immunohistochemical and molecular markers intended for risk stratification are of particular value in oncomorphology. They help identify patients requiring intensified treatment.

Among them, the p53 protein plays a crucial role: in microscopic examination, its aberrant staining has diagnostic significance, which can be visualized either as total overexpression or as global loss of expression. Beta-catenin is evaluated by clinicians based on the presence of pathological nuclear expression. Mismatch repair system (MMR) markers are critical for screening for colorectal cancer in individuals whose pathology is associated with hereditary Lynch syndrome. Indicators PD-1 and PD-L1 demonstrate high prognostic significance when examining patients suffering from poorly differentiated upper urinary tract urothelial cancer.

Despite rapid progress in diagnostics, there is a serious limitation. Potential molecular predictors of therapy response, such as RRM1 and CYP2W1, have not currently undergone sufficient validation for implementation. Moreover, when working with rare nosologies, none of the known markers is yet recommended for routine daily use. The reason lies in objective flaws in the conducted studies—in particular, their retrospective design and overly small clinical sample sizes.

Genetic variants and hereditary predisposition

To standardize the exchange of genetic data, the American College of Medical Genetics and Genomics (ACMG) has developed a rigorous system for interpreting nucleotide sequence variants. Of greatest interest is pathogenicity class V. This group includes exclusively those genetic variants that are the definitively proven root cause of disease development. In medical and laboratory documentation, such findings are recorded using standard entry forms: "Pathogenic", abbreviated as "Path" or by the Latin letter "P".

When analyzing the genetic basis of diseases with hereditary predisposition (multifactorial pathologies), two main mechanisms are distinguished. The polygenic form of the disease is due to the cumulative effect of multiple altered genes. The monogenic form, conversely, is directly associated with a defect in only one specific gene. Nevertheless, it is critically important to realize that for the phenotypic manifestation of the disease in the monogenic form, exposure to specific environmental triggering factors that act as a trigger for the pathological process is mandatory.

Class and exam questions

What else to study on this topic

• Flow cytometry technology: principles of assessing remission.
• Evaluation of aberrant p53 protein staining: overexpression vs. total loss.
• The role of the MMR repair system in colorectal cancer screening in Lynch syndrome.
• Epithelial-mesenchymal transition as a key stage of invasion and metastasis.
• ACMG criteria: detailed analysis of pathogenicity classes of genetic variants.

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.