Hereditary predisposition
Genetic factors play a key role in oncogenesis. There are about 20 hereditary pathologies that significantly increase the likelihood of malignant transformation.
- Li-Fraumeni syndrome: an autosomal dominant disorder associated with a mutation in the p53 gene. It provokes a wide spectrum of tumors, including sarcomas, leukemias, and breast cancer.
- Genome instability syndromes: Fanconi anemia, Bloom syndrome, and ataxia-telangiectasia (Louis-Bar syndrome) create conditions for the development of leukemia in children.
- Family history: the risk of developing tumors in siblings is 2–4 times higher, and in monozygotic twins, the incidence of leukemia can reach 25%.
Suppressor gene defects
Normally, suppressor genes limit uncontrolled cell division. Their damage removes the "brakes" from the cell cycle:
- TP53 gene: a critical regulator whose defect underlies Li-Fraumeni syndrome.
- MADH4 gene: a deletion at the 18q21.1 locus is associated with colorectal and pancreatic cancer.
- Impaired adhesion: a decrease in E-cadherin expression disrupts intercellular contacts, which directly promotes tumor metastasis.
Chromosomal aberrations
Structural chromosomal changes often become the initiating mechanism of tumor growth:
- Philadelphia chromosome: the result of a reciprocal translocation between chromosomes 9 and 22. The fusion of the BCR and ABL1 genes leads to the activation of tyrosine kinase, which provokes myeloid leukemia.
- Deletions: frequently detected in osteosarcomas and retinoblastomas, depriving the cell of important regulatory DNA segments.
Environmental and immune factors
In addition to genetics, ecological and immunological conditions influence the risk:
- Immunodeficiency: low activity of anti-tumor defense mechanisms prevents the body from eliminating transformed cells in a timely manner.
- Geographical features: an uneven distribution of neoplasms is observed. For example, gastric cancer is endemic to Japan and Argentina, while esophageal cancer is endemic to Southeastern China.
Briefly: answers to topical questions
Which chemical substances are exogenous carcinogens?
Exogenous chemical carcinogens include several classes of substances.
Main groups:
- Polycyclic aromatic hydrocarbons — 3,4-benzopyrene, 20-methylcholanthrene, dimethylbenzanthracene; sources include tobacco smoke, exhaust fumes, smoked foods.
- Aromatic amines and amides — 2-naphthylamine, 2-aminofluorene, benzidine; aniline dyes are associated with bladder tumors.
- Nitroso compounds — diethylnitrosamine, dimethylnitrosamine, nitrosomethylurea.
- Aminoazo compounds — 4-dimethylaminoazobenzene, ortho-aminoazotoluene.
- Heterocyclic aromatic hydrocarbons — dibenzacridine, dibenzcarbazole.
- Aflatoxins — metabolic products of molds, predominantly Aspergillus flavus.
- Other organic substances — epoxides, plastics, urethane, carbon tetrachloride, chloroethylamines.
- Metals; occupational hazards associated with lung cancer also include asbestos, arsenic, chromium, and nickel.
Which viruses have proven oncogenic activity in humans?
Both DNA-containing and RNA-containing viruses possess oncogenic activity in humans.
Main human virus-tumor associations:
- Epstein-Barr virus — a DNA virus; associated with endemic (African) Burkitt lymphoma and nasopharyngeal carcinoma.
- Human papillomavirus — a DNA virus; associated with papillomas, skin, and genital cancers.
- HTLV-I — an RNA virus; associated with certain types of T-cell leukemias and lymphomas.
Which specific cells of the immune system perform anti-tumor surveillance?
Anti-tumor immune surveillance is carried out by several types of effector cells.
The main role in destroying tumor cells is played by:
- Natural killer (NK) cells — destroy cells without prior sensitization, polyclonally recognizing stress molecules MICA and MICB. In the liver, their function is performed by pit cells.
- Cytotoxic T lymphocytes (CTLs) — mature from CD8+ cells, specifically recognize membrane-bound tumor antigens associated with MHC class I.
- Macrophages — carry out non-specific damage (by secreting TNF-α) and specific damage (by attaching to Fc fragments of anti-tumor antibodies). In the liver, phagocytosis is provided by hepatic stellate cells (Kupffer cells).
"Suppressor genes are the brakes: if p53 or E-cadherin are broken, the cell rushes toward metastasis without stopping."
Class and exam questions
Why does Li-Fraumeni syndrome give rise to so many different tumors?
Because the p53 gene is the universal "guardian of the genome." Its defect deprives cells of the ability to repair DNA damage or trigger apoptosis, making them vulnerable to any carcinogens.
How does the Philadelphia chromosome cause leukemia?
As a result of the translocation, a chimeric gene is formed that encodes a hyperactive tyrosine kinase. This protein constantly signals the cell to divide, bypassing natural control mechanisms.
What is decreased E-cadherin expression?
This is the loss of proteins responsible for "gluing" cells together. Without them, tumor cells lose contact with neighbors and gain the ability to detach from the primary node, which leads to metastasis.
What else to study on this topic
- Mechanisms of ultraviolet radiation's effect on carcinogenesis.
- The role of tyrosine kinases in proliferative signal transduction.
- Epidemiological theories of gastric cancer distribution.
- The relationship between agammaglobulinemia and oncopathology.
- Molecular mechanisms of loss of heterozygosity at the 10q23 locus.
Master the entire topic in the "Pathophysiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Risk factors for tumor growth" and 4,913 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 135 video lessons on the subject
Other topics in "Chapter 17. NEOPLASMS"
Free video lessons: pathophysiologyShort lessons with lecture notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.