Topic 36. Basis of Oncology
Morphological and Biological Aspects of Tumors, Growth, Precancer, Initial Cancer, Hereditary Tumors, Carcinoma in situ
Definition of Tumor
A tumor (neoplasm) is a pathological process of uncontrolled, abnormal cell and tissue growth due to loss of normal regulation of the cell cycle. It may be:
- Benign (localized, slow- growing, non- invasive)
- Malignant (fast- growing, invasive, and capable of metastasis)
Morphological Aspects of Tumors
- Cytological atypia: nuclear enlargement, hyperchromasia (increased staining intensity of a cell's nucleus ), increased mitotic activity
- Architectural distortion: loss of polarity, abnormal structures
- Invasion: penetration of basal membrane in malignancy
- Metastasis: spread to lymph nodes or distant organs (only in malignant tumors)
Biological Aspects of Tumors
Carcinogenesis:
Stepwise transformation of normal cells → malignant cells due to:
- Genetic mutations
- Epigenetic alterations
- Deregulated growth signals
Key terms:
Tumor Growth
Phases
- Initiation – DNA damage occurs (approx. 10⁴ cells)
- Promotion – Proliferation and clonal expansion (approx. 10⁶ cells)
- Progression – Tumor acquires mutations, angiogenesis, invasion (≈ 10⁹ cells)
Tumors may grow due to:
- Autocrine signaling (self- stimulation of growth)
- Mutation in growth factor pathways (e.g. MAPK)
- Loss of apoptosis (↑ Survivin → ↓ Caspase activation)
Precancerous Lesions
Precancers are lesions with a risk of developing into malignancy.
Two types:
- Facultative: Low risk (e.g. hyperplasia of prostate)
- Obligatory: High risk (e.g. adenomatous polyps of colon)
Examples:
Initial Cancer
- Early malignant tumor confined to mucosa/submucosa
- No invasion into muscularis propria
- Potential for complete cure if detected early
Hereditary Tumors
Transmitted via germline mutations, often autosomal dominant.
Examples:
Carcinoma in situ (CIS)
- Pre-invasive malignant tumor
- Confined to epithelium
- No breach of basement membrane
- No lymphatic or blood spread
Histological Features:
- Full- thickness epithelial dysplasia
- Intact basal membrane
- No vascular/lymphatic invasion
Common sites:
- Cervix (CIN III)
- Bladder (CIS of urothelium)
- Skin (Bowen’s disease)
- Breast (DCIS – Ductal carcinoma in situ)