Histological Classification of Neoplasia in UC

All pathological slides of neoplasia were re-reviewed and classified in accordance with the most recent World Health Organization classification [30 ] by two expert gastrointestinal pathologists (YA and SC); one of whom (YA) was highly specialized in UC-associated dysplasia or cancer.
We classified neoplasia into five categories on the basis of the histological findings and whether the neoplasia was located in colitis-affected segments, as follows: serrated polyps in colitis-affected segments, conventional dysplasia (intestinal-type dysplasia in colitis-affected segments), serrated polyps in colitis-unaffected segments (usually proximal to the extent of the colitis), sporadic adenomas in colitis-unaffected segments, and invasive carcinoma. Additionally, serrated polyps in colitis-affected segments were histologically classified into three subtypes in accordance with previous studies [27 (link)–29 (link)], as follows: SSL-like dysplasia, TSA-like dysplasia, and serrated SD NOS. Briefly, SSL-like dysplasia is characterized by distorted serrated crypts with prominent basal crypt dilatation (i.e., dilated L- or inverted T-shaped crypts) at the interface with the muscularis mucosa. TSA-like dysplasia is characterized by a villiform growth pattern with columnar cells with intensely eosinophilic cytoplasm and ectopic crypts, creating a prominent serrated profile. SD NOS was defined as serrated dysplasia without definite features of SSL-like or TSA-like dysplasia, with a complex serrated architecture and evidence of dysplasia [27 (link)–29 (link)]. The representative endoscopic and histological features of SSL-like dysplasia, TSA-like dysplasia, and SD NOS are shown in S1 Fig. Serrated polyps in colitis-unaffected segments were classified as hyperplastic polyps, SSLs, TSAs, or unclassified serrated adenomas [30 ].