Characterisation of precursor lesions in colorectal cancers with DNA instability

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It is now generally accepted that most colorectal cancers arise from previously benign lesions in the mucosal lining of the large bowel. These lesions are called adenomatous polyps. They have been extensively studied as have the cancers which evolve from them with regard to the type of cancer causing genetic changes they bear. Recently, it has been found that colorectal cancer is not a single disease in that there exists a subgroup comprising 15% of colorectal cancers which is an entirely different type wwith respect to genetic changes and biological behaviour. This subgroup contains cancers with a high level of microsatellite instability (MSI-high) and the cancers which comprise this group show none of the common genetic changes which can be demonstrated in both adenomatous polyps and the 85% of colon cancers which develop from them. The MSI-high colorectal cancers do however share some striking similarities to a type of polyp (hyperplastic) which has until quite recently been considered of little consequence. Our research group and others have shown an association with colorectal cancer in those patients in whom hyperplastic polyps are unusually large or numerous, especially if present in the right side of the large bowel, where the bulk of MSI-high colorectal cancers arise. The current proposal will investigate the hyperplastic polyp as a precursor lesion in the genesis of MSI-high cancers.