Tumor and its properties
Neoplasia is an uncontrolled monoclonal proliferation of cells that can be benign or malignant. Tumor is defined as a pathological excessive tissue mass with uncoordinated, unregulated, and autonomous growth that continues even after the removal of the factor that caused it. This growth is caused by damage to the genome of the progenitor cell: all progeny originate from a single cell with altered DNA.
Key characteristics of the tumor process:
- Autonomous growth: uncontrolled cell division.
- Atypia: changes in structure, metabolism, functions, antigenic profile, reproduction, and differentiation.
- Anaplasia: backward development, loss of differentiation.
- Cataplasia: acquisition of new properties by cells.
The tumor consists of parenchyma (the actual tumor cells that determine the behavior of the neoplasm) and stroma (connective tissue, blood vessels, infiltrate, forming the framework).
Etiology and carcinogenesis
The development of tumors is associated with the action of carcinogenic factors:
- Chemical (about 75% of cases): tobacco smoke, benzpyrene, aniline dyes, aflatoxins. Divided into direct and indirect.
- Physical: ultraviolet radiation (skin cancer), ionizing radiation.
- Viral: DNA viruses (Epstein–Barr, hepatitis B and C, human papillomavirus) and RNA viruses.
- Microbial: for example, Helicobacter pylori, which increases the risk of gastric cancer.
Carcinogenesis is a multistep process involving an initiation phase (DNA mutation) and promotion (action of promoters). There are viral-genetic, physico-chemical (Virchow), and dysontogenetic (Cohnheim) theories of the origin of malignant tumors.
Benign epithelial tumors
Epithelial tumors without specific localization develop from squamous or glandular epithelium (epidermis, mucous membranes of the oral cavity, esophagus, endometrium, urinary tract). Benign forms retain normal cell structure, do not show invasion, possess only tissue atypia, but under certain conditions can undergo malignant transformation.
Papilloma (from Lat. papilla — nipple) develops from squamous or transitional epithelium. It has a spherical shape, dense or soft consistency, a surface with papillary outgrowths resembling cauliflower. Sizes vary from a millet seed to a large pea. Cellular polarity, cohesiveness, and the basement membrane are preserved. Often associated with HPV (especially types 6 and 11).
Adenoma is a benign tumor of glandular epithelium. It occurs in organs with epithelial parenchyma (liver, kidneys, endocrine glands) and in hollow organs with mucous glands. It is a demarcated node of soft consistency, white-pink on cross-section, sometimes with cysts. An adenoma of the mucous membrane protruding above the surface is called an adenomatous polyp. Acinar, tubular, trabecular, and papillary forms are distinguished.
Carcinoma in situ and squamous cell carcinoma
Cancer is a malignant neoplasm (MN) originating from epithelium; epithelial tumors account for 80–90% of all MNs. Distinctive features include cellular atypia, pathological mitoses, and invasive growth.
Carcinoma in situ is an intraepithelial, non-invasive cancer with pronounced atypia and pathological mitoses. Growth is restricted to the epithelial layer, and the basement membrane is not destroyed. This is the initial stage of cancer, at which treatment is most effective.
Squamous cell carcinoma develops on the skin and mucous membranes lined with squamous or transitional epithelium (oral cavity, esophagus, cervix, vagina), and on mucous membranes with columnar epithelium after metaplasia. Atypical cells grow into the tissues, forming nested clusters. Upon keratinization, cancer pearls are formed. Often associated with UV radiation and tobacco carcinogens.
Adenocarcinoma and its variants
Adenocarcinoma (glandular cancer) forms from the columnar epithelium of mucous membranes and glands. The structure resembles an adenoma, but with added cellular atypia: variable cell shape, hyperchromatic nuclei, loss of the basement membrane, and invasive growth. Acinar, tubular, and papillary forms are distinguished.
- Mucinous (colloid) carcinoma: glandular structures become overfilled with mucus, rupture, and form "pools of mucus".
- Signet-ring cell carcinoma: cells are engorged with mucus, pushing the nucleus to the periphery, which gives a signet-ring appearance.
- Solid (trabecular) carcinoma: undifferentiated, cells are arranged in trabeculae separated by connective tissue; rapid growth, early metastasis; characteristic of the liver and thyroid gland.
Low-differentiated forms of cancer
The lower the cell differentiation, the higher the malignancy and the more difficult the treatment.
- Small cell carcinoma: undifferentiated, consisting of monomorphic lymphocyte-like cells with scant stroma, numerous mitoses, and necrosis; characterized by rapid growth and early metastasis. Often associated with smoking; typical localization is the lungs.
- Fibrous carcinoma (scirrhus): undifferentiated cancer with atypical hyperchromatic cells in a coarse-fibered stroma that predominates over the parenchyma. Distinguished by high malignancy and early metastasis; characteristic of the breast.
- Medullary (medullary/adenoid) carcinoma: predominance of parenchyma over minimal stroma, soft consistency, white-pink color, resembling brain tissue; numerous mitoses, rapid growth, early metastasis; often found in the thyroid gland.
- Dimorphic carcinoma: a mixed form arising from squamous and columnar epithelial rudiments; found in the ovaries and esophagus.
Key points
- A tumor consists of parenchyma (determines behavior) and stroma (framework).
- Epithelial tumors account for 80–90% of all malignant neoplasms due to the high proliferative activity of the epithelium.
- Benign epithelial tumors—papilloma and adenoma—exhibit only tissue atypia.
- Cellular atypia and pathological mitoses are morphological signs of malignancy.
- Carcinoma in situ does not destroy the basement membrane and is the most favorable for treatment.
- Squamous cell carcinoma can form cancer pearls upon keratinization.
- Signet-ring cell, mucinous, solid, small cell, fibrous, and medullary carcinomas are poorly differentiated aggressive forms.
- The degree of cell differentiation is inversely proportional to tumor malignancy.