General Characteristics of Tumors
Tumor (neoplasm): An abnormal mass of tissue, growth exceeds and is uncoordinated compared to normal tissues, persists even after the cessation of the initial stimulus.
Key Features
Autonomous growth.
Excessive and unregulated.
Clonal origin (arises from one transformed cell).
Classification of Tumors
1 Based on behavior
Benign tumors:
- Slow growth.
- Localized, non- invasive.
- Well- differentiated.
- Rarely life- threatening (except in critical locations).
Malignant tumors (cancers):
- Rapid growth.
- Invasive, infiltrative.
- Poorly differentiated (anaplasia).
- Metastasize to distant sites.
2 Based on tissue of origin
Epithelial origin
Benign: Adenoma, papilloma.
Malignant: Carcinoma (e.g., squamous cell carcinoma, adenocarcinoma).
Mesenchymal origin
Benign: Lipoma, fibroma.
Malignant: Sarcoma (e.g., osteosarcoma, leiomyosarcoma).
Others
Hematopoietic and lymphoid: Leukemias, lymphomas.
Germ cell tumors: Seminoma, teratoma.
Neuroectodermal: Neuroblastoma, glioblastoma.
Etiology of Tumors (Carcinogenesis)
1 Genetic factors
Familial predisposition (e.g., retinoblastoma, familial adenomatous polyposis).
Inherited cancer syndromes due to mutations in tumor suppressor genes (e.g., BRCA1/ 2 in breast cancer).
2 Environmental factors
Chemical carcinogens:
- Polycyclic aromatic hydrocarbons (tobacco smoke → lung cancer).
- Aflatoxin B1 (hepatocellular carcinoma).
Physical carcinogens:
- UV radiation (skin cancers).
- Ionizing radiation (thyroid cancer, leukemias).
Biological agents:
- Viruses (e.g., HPV in cervical cancer, EBV in Burkitt lymphoma).
- Bacteria (e.g., Helicobacter pylori in gastric adenocarcinoma).
3 Hormonal factors
Estrogens (endometrial carcinoma).
Androgens (prostatic carcinoma).
4 Chronic inflammation and immunologic factors
Chronic gastritis (gastric carcinoma).
Ulcerative colitis (colorectal carcinoma).