Knudson hypothesis
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The Knudson hypothesis is the hypothesis that cancer is the result of accumulated mutations to a cell's DNA. It was first formulated by Alfred G. Knudson in 1971, and led indirectly to the identification of cancer-related genes. Knudson won the 1998 Albert Lasker Medical Research Award for this work.
Knudson performed a statistical analysis on cases of retinoblastoma, a tumour of the retina which occurred both on children as a hereditary disease and in adults in a sporadic fashion. In addition, the children often developed the tumour in both eyes, suggesting an underlying predisposition.
The findings were that multiple "hits" to DNA were necessary to cause cancer. In the children with retinoblastoma, the first insult was congenital, and any second insult would rapidly lead to cancer. In adult cases, two "hits" had to take place before a tumour could develop, explaining the age difference.
It was later found that carcinogenesis (the development of malignancy) depended both on the activation of oncogenes (genes that stimulate cell proliferation) and tumor suppressor genes (genes that keep proliferation in check). A first "hit" in an oncogene would not necessarily lead to cancer, as normally functioning tumor suppressor genes would still counterbalance this impetus; only damage to TSGs would lead to unchecked proliferation. Conversely, a damaged TSG (such as the Rb1 gene in retinoblastoma) would not lead to cancer unless there is a growth impetus from an activated oncogene.
Field cancerisation may be an extended form of the Knudson hypothesis. This is the phenomenon of various primary tumours developing in one particular area of the body, suggesting that an earlier "hit" predisposed the whole area for malignancy.
The multi-mutation theory on cancer was first proposed by Carl O. Nordling in the British Journal of Cancer in 1953. He noted that in industrialized nations the frequency of cancer seems to increase according to the sixth power of age. This correlation could be explaned by assuming that the outbreak of cancer requires the accumulations of six consecutive mutations.
[edit] References
- Knudson AG Jr. Mutation and cancer: statistical study of retinoblastoma. Proc Natl Acad Sci U S A 1971;68:820-3. PMID 5279523.
- Nordling, Carl O. A New Theory on the Cancer-inducing Mechanism, originally published in the British Journal of Cancer, 1953, Vol. VII, p. 68-72.
