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
| Benign | | | Malignant | |
| Usually well differentiated | | | Lack of differentiation is typical | |
| Grow slowly | | | Grow rapidly | |
| Grow as cohesive expansile masses | | | Infiltrate the surrounding tissue | |
| Typically form a fibrous capsule | | | Do not form a capsule | |
| Compress the surrounding tissue | | | Invade and destruct the surrounding tissue | |
| Do not metastasize | | | Metastasize | |
| Do not cause cachexia | | | Cause cachexia | |
| Do not recidivate | | | Recidivate | |