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Multiple mutations underlie the development of cancer

Multiple mutations underlie the development of cancer -...

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Multiple mutations underlie the development of cancer. More than one somatic mutation is generally needed to produce the changes characteristic of a  full-fledged cancer cell. If cancer results from an accumulation of mutations, and if mutations occur throughout life,  then the longer we live, the more likely we are to develop cancer. Colorectal cancer, with 135,000 new cases and 60,000 deaths in the United States each year,  illustrates a multistep cancer path. o The first sign is often a polyp, a small benign growth in the colon lining. o The cells of the polyp look normal but divide unusually frequently. o Through gradual accumulation of mutations that activate oncogenes and knock out tumor- suppressor genes, the
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Unformatted text preview: polyp can develop into a malignant tumor. A ras oncogene and a mutated p53 tumor-suppressor gene are usually involved. About a half dozen DNA changes must occur for a cell to become fully cancerous. ○ These changes usually include the appearance of at least one active oncogene and the mutation or loss of several tumor-suppressor genes. ○ Because mutant tumor-suppressor alleles are usually recessive, mutations must knock out both alleles. ○ Most oncogenes behave like dominant alleles and require only one mutation. ○ In many malignant tumors, the gene for telomerase is activated, removing a natural limit on the number of times the cell can divide....
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