Typical forms of abnormal tissue growth include:
• pathological hypertrophy and hyperplasia;
• pathological hypotrophy and atrophy;
• metaplasia;
• dysplasia;
• benign tumor;
• malignant tumor.
TUMORS
The essential property of all tumors may be defined as excessive growth of abnormal (atypical) cells.
Abnormality of tumor cells takes various forms.
• Abnormal proliferation.
• Abnormal differentiation.
• Abnormal metabolism or energy production.
• Physico-chemical abnormality.
• Abnormal functioning.
• Antigenic abnormality.
• Morphological abnormality.
• Abnormal cell-to-cell interactions.
The principal targets of genetic damage during neoplastic transformation of a cell are three classes of normal regulatory genes:
• the growth-promoting protooncogenes;
• the growth-inhibiting cancer-supressor genes (antioncogenes);
• genes that regulate programmed cell death (apoptosis);
• genes that regulate repair of damaged DNA.
Mechanisms of transformation of protooncogene to oncogene.
• Integration of proviral DNA near protooncogene.
• Insertion of retroviral promoter in the close vicinity of protooncogene.
• Mutations of protooncogenes (including genes for growth factor, or growth factor receptor).
• Overexpression or amplification of protooncogene.
Differences between benign and malignant tumors
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Usually well differentiated | Lack of differentiation is typical |
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Grow as cohesive expansile masses | Infiltrate the surrounding tissue |
Typically form a fibrous capsule | |
Compress the surrounding tissue | Invade and destruct the surrounding tissue |
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Three main concepts of carcinogenesis:
1) chemical carcinogenesis;
2) viral carcinogenesis;
3) radiation carcinogenesis.
Chemical carcinogenesis
Chemicals that initiate carcinogenesis fall into one of two categories:
1) direct-acting compounds, which do not require chemical transformation for their carcinogenicity;