Differences in the distribution of acidic mucins between flat tubular adenomas and flat serrated adenomas of the colorectal mucosa.

Two consecutive sections from 72 endoscopically detected flat colorectal polyps (flat tubular adenomas n = 40, flat serrated adenomas n = 18, flat hyperplastic polyps n = 7 and normal colonic mucosa n = 7) were stained with Alcian blue pH 2.5 (AB) or with high iron diamine (HID) without counterstain, to evidence the most important attribute of the colorectal cells i.e. their capacity to produce acidic mucins (sialomucins and sulphomucins respectively). Intense AB and HID staining (++) was found in the upper part of the crypts of all (100%) sections with normal colonic mucosa or with flat hyperplastic polyps, in 13 of the 18 (72%) flat serrated adenomas (with low grade dysplasia = LGD, n = 16; or high grade dysplasia = HGD, n = 2) but in none (0%) of the 40 tubular adenomas. Slight (+) or negative staining of the upper part of the crypts were recorded in all 40 (100%) flat tubular adenomas (LGD n = 32; HGD, n = 8), but in only 5 of the 18 (27,7%) flat serrated adenomas (LGD n = 3; HGD n = 2) and in none (0%) of the sections with normal colonic mucosa or with flat hyperplastic polyps. Intense AB and HID staining (++) was found in the lower part of the crypts in all sections (100%) with normal mucosa or with flat hyperplastic polyps, in 36 of the 40 flat (90%) tubular adenomas (LGD n = 32; HGD n = 8), but in none (0%) of the flat serrated adenomas. Slight (+) or negative stainings in the lower part of the crypts were recorded in all 18 (100%) flat serrated adenomas, but in only 4 of the 40 (10%) flat tubular adenomas and in none of the sections (0%) with normal mucosa or with flat hyperplastic polyps. Thus, the mucosal localization of the depletion of mucin production differs in flat serrated adenomas and in flat tubular adenomas. The difference in topographic distribution of the depletion of acidic mucins in epithelial cells is a new argument in favour of the identity of flat serrated adenomas as an independent neoplastic phenotype in the colorectal mucosa.