Key Differences Between Tumor Tissue and Normal Tissue
Any neoplasm cardinally differs from healthy body tissues by a number of unique biological properties. These differences determine the severity of the pathological process:
- Link to genome alterations. The primary cause of tumor growth always lies in damage to the genetic apparatus of cells. In the vast majority of cases, somatic mutations are responsible. Germline mutations are significantly less common (in hereditary or familial cancer syndromes).
- Autonomous and uncontrolled growth. Cell division is no longer controlled by the normal regulatory stimuli of the host organism. The tumor obeys exclusively its own autonomous regulation, constructed by the pathological cells themselves and their supporting stroma.
- Profound disruption of the cell cycle and differentiation. There is a marked imbalance between proliferation (reproduction) and cell death. Pathological mitotic figures are frequently found under the microscope.
- Pathology of apoptosis. Programmed cell death in neoplasms is incomplete and characterized by relative insufficiency.
- Growth stimulation via cell death. This is one of the most paradoxical mechanisms: the death of tumor cells does not stop, but rather stimulates further growth of the neoplasm. During incomplete apoptosis, specific mitogenetic factors are released from disintegrating apoptotic bodies, forcing neighboring cells to actively divide.
Types of Tumors and Their Clinical Behavior
In pathology, all neoplasms are traditionally divided into three large groups. This classification is based on four key criteria: the degree of maturity of cellular elements, growth rate and pattern, metastatic potential, and tendency to recur.
| Characteristic | Benign | Malignant | Borderline |
|---|---|---|---|
| Cellular structure | Mature, differentiated | Undifferentiated or partially mature | Mature, differentiated |
| Growth pattern | Slow, expansile (with a capsule) | Rapid, infiltrative and invasive | Invasive |
| Recurrence and metastasis | Do not recur, do not metastasize | Recur and metastasize | Capable of recurring |
Benign tumors grow "within themselves" (expansile growth). They do not destroy neighboring structures, but merely gently push them aside, forming a distinct connective tissue capsule at the border with healthy tissue.
Malignant tumors grow aggressively. They are characterized by infiltrative growth (destructive invasion into surrounding tissues) and invasive growth (invasion into blood and lymphatic vessels). Secondary changes frequently occur within their tissue: foci of necrosis, massive hemorrhages, myxoid change (mucoid degeneration), and calcification (petrification).
> Clinical significance: Although the prognosis for these diseases is becoming increasingly optimistic, malignant tumors remain the second leading cause of death in developed countries (after cardiovascular disease).
Principles of Nomenclature
Medical nomenclature of neoplasms is built on a strict principle: the suffix "-oma" is added to the root name of the tissue of origin.
Classification by histogenesis (tissue origin) includes the following basic terms:
- Benign formations originating from epithelial tissue are called epitheliomas.
- Malignant formations originating from epithelium are termed carcinoma (carcinoma).
- Malignant formations of mesenchymal origin are called sarcomas (sarcoma).
Important terminological distinction: In English-language medical literature, the word cancer denotes absolutely any malignant tumor, regardless of the tissue of origin. However, in professional Russian-language literature, the term "rak" (carcinoma/cancer strictly speaking) is applied exclusively to malignant tumors originating from the epithelium.