PMC

High-power field of a serrated adenoma with high-grade dysplasia (A) in which there is aberrant nuclear expression of p53 (B) and loss of nuclear expression of O-6-methylguanine DNA methyltransferase (C).

A, Serrated adenoma (SA) (BRAF mutation) with a ‘hyperplastic’ appearance but with architectural and cytological features of a non-adenomatous form of dysplasia. The latter include marked epithelial serration and surface papillarity and nuclei that are ovoid, vesicular and contain a prominent nucleolus (inset). The columnar cells (inset) contain apical mucin droplets, similar to sessile SA (SSA). B, Mixed polyp (BRAF mutation) comprising SSA (left) and SA with high-grade dyplasia showing back-to-back glands (right) and aberrant expression of p53 (inset). C,D, Two mixed polyps (MPs) (both SA/tubulo-villous adenoma and with KRAS mutation) in which the serrated epithelium has an adenomatous appearance as evidenced by elongated hyperchomatic nuclei with marked stratification and a dark amphophilic cytoplasm. The pure adenomatous component is not shown. E,F, Low- and medium-power images of a SA (KRAS mutation) in which complex microacini have resulted in markedly serrated epithelial contours. The epithelium comprises numerous goblet cells and absorptive-type columnar cells with eosinophilic cytoplasm and is reminiscent of the goblet cell variant of hyperplastic polyp. These examples illustrate the range of appearances and genetic changes that are encompassed by ‘traditional’ SA.