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Knudson AG
Hereditary cancer: Two hits revisited
Journal of Cancer Research and Clinical Oncology. 1996 Mar;122(3) :135-140
PMID: ISI:A1996TW04000001   
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Abstract
According to a ''two-hit'' model, dominantly inherited predisposition to cancer entails a germline mutation, while tumorigenesis requires a second, somatic, mutation. Non- hereditary cancer of the same type requires the same two hits, but both are somatic. The original tumor used in this model, retinoblastoma, involves mutation or loss of both copies of the RBI tumor-suppressor gene in both hereditary and non-hereditary forms. In fact, most dominantly inherited cancers show this relationship. New questions have arisen, however. When a tumor- suppressor gene is ubiquitously expressed, why is there any specificity of tumor predilection? In some instances, it is clear that two hits produce only a benign precursor lesion and that other genetic events are necessary. As the number of necessary events increases, the impact of the germline mutation diminishes. The number of events is least for embryonal tumors, and relatively small for certain sarcomas. Stem-cell proliferation evidently plays a key role early in carcinogenesis. In some tissues it is physiological, as in embryonic development and in certain tissues in adolescence. In adult renewal tissues, the sites of the common carcinomas, mutation may be necessary to impair the control of switching between renewal and replicative cell divisions; the APC gene may be the target of such a mutation.
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Times Cited: 101 English Article TW040 J CANCER RES CLIN ONCOL