Serrated adenoma of the colorectum and the DNA-methylator phenotype

Epithelial polyps of the colorectum have traditionally been classified into two main groups: neoplastic polyps or adenomas, and hyperplastic polyps. Serrated adenomas display features intermediate between hyperplastic polyps and adenomas. The absence of serrated adenomas in recently published series of colorectal polyps indicates that some pathologists do not recognize them. Yet, it is becoming increasingly clear that serrated adenoma serves as the precursor lesion for a major subset of colorectal cancers. It is likely that a significant proportion of these lesions do not evolve through the adenoma-to-carcinoma sequence, but through a largely independent 'serrated-polyp pathway' in which DNA methylation is a key genetic hallmark. Jass discusses the importance of the 'CpG-island-methylator phenotype' and the morphological and molecular correlations of serrated adenomas.