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13. TYPICAL DISORDERS OF TISSUE GROWTH. TUMORS

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

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;

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