[Non-serrated precursor lesions of colorectal tumours]

Non-serrated precursor lesions of colorectal tumours include conventional adenomas (tubular, tubulovillous and villous), inflammatory bowel disease-associated dysplasia (intraepithelial neoplasia), and hamartoma-associated dysplasia. This short review summarizes the current literature on the adenoma-carcinoma sequence, focusing on colonic stem cells and functional crypt organization, patterns of stem cell division, niche succession and clonal conversion in the formation of a monocryptal adenoma. The process of clonal interaction between neighboring crypts as well as the development of large monoclonal adenomas from small polyclonal precursor lesions is discussed in detail. Finally, the molecular pathogenesis as well as the clinical significance of inflammatory bowel disease- and hamartoma-associated carcinogenesis is addressed.