'Serrated' adenoma of the colorectum, with reference to its gastric differentiation and its malignant potential

Serrated adenoma of the colorectum was a newly proposed entity in 1990, cha racterized by epithelial neoplasia combining the architectural features of a hyperplastic (metaplastic) polyp with the cytological features of an aden oma, Its histonenesis and natural history still remain unclear. Forty-six s errated adenomas were obtained from 46 patients, The clinicopathological fe atures mere summarized, Paraffin-embedded blocks from 34 serrated adenomas were available for immunohistochemical studies using pS2, human gastric muc in, and p53 protein. Eighteen hyperplastic (metaplastic) polyps, 16 tubular adenomas, and 12 early-stage adenocarcinomas were randomly selected as con trol groups for immunohistochemical analysis. The patients' ages ranged fro m 32 to 86 (average 61.4) gears. Males were more frequently affected than f emales. Serrated adenomas were predominantly present in the left-side of th e colon and in the rectum (72 per cent). Their sizes ranged from 3 to 26 mm (average 9.2 mm), Six lesions (13 per cent) contained foci of high-grade d ysplasia. These adenomas were significantly larger (12.7 mm) than those con taining no high-grade dysplasia (8.6 mm). pS2 and human gastric mucin were expressed significantly more frequently in both hyperplastic (metaplastic) polyps and serrated adenomas than in tubular adenomas or adenocarcinomas, p 53-positive cells were present in 18 of the 29 pure serrated adenomas (62 p er cent) and in one of the five areas of low-grade dysplasia in serrated ad enomas with high-grade dysplasia (20 per cent), most of which revealed a sp oradic distribution, Only five of the 29 serated adenomas with no high-grad e dysplasia (17 per cent) were regarded as demonstrating p53 overexpression . On the other hand, three of the five areas of high-grade dysplasia in ser rated adenomas (60 per cent) revealed diffuse positivity (3+) for p53 prote in. The serrated adenoma, which possibly shows gastric differentiation, is considered to be an independent histological entity among the various pheno types of colorectal adenomas, Serrated adenoma would seem to be a precursor of carcinoma, its potential for malignant transformation being similar to that of the traditional tubular adenoma. It mould also seem that p53 is inv olved in the serrated adenoma-carcinoma sequence. Copyright (C) 1999 John W iley & Sons, Ltd.