AIMS: Evaluation of dysplasia in long standing ulcerative colitis is a difficult and often subjective task. Therefore, the aim of this study was to search for a more objective parameter to help distinguish regenerative changes from epithelial dysplasia. METHODS: A total of 97 sections from colectomy specimens from 12 patients with ulcerative colitis of more than 10 years duration were stained immunohistochemically with MIB 1 to detect differences in the frequency and pattern of nuclei positive for the proliferation marker Ki-67. All patients had epithelial dysplasia in one or more areas (high grade dysplasia, n = 16; low grade dysplasia, n = 15; indefinite for dysplasia, n = 16), and three patients had additional adenocarcinoma (one Dukes's C multifocal, mucinous carcinoma; one Dukes's C adenocarcinoma in the sigmoid; and one Dukes's A adenocarcinoma in the caecum). Two patients had adenomas--one had an 8 cm villous adenoma with intramucosal carcinoma, and the other had a 4 cm tubulovillous adenoma with high grade dysplasia. RESULTS: There were highly significant differences between the percentages of Ki-67 immunopositive cells in low grade and high grade dysplasia and carcinoma compared with regenerative epithelium. In high grade dysplasia and carcinoma, the distribution of Ki-67 positive cells was diffuse throughout the full length of the crypt, whereas low grade dysplasia and epithelium indefinite for dysplasia, as well as regenerative epithelium, showed an expanded basal zone. CONCLUSIONS: Assessment of the number of Ki-67 immunostained cells is of additional value in deciding whether the mucosa is regenerative or dysplastic, and the MIB 1 staining pattern is characteristic for most lesions with high grade dysplasia and carcinoma. Therefore, this technique could be combined with routine histological evaluation of colorectal epithelium being examined for dysplasia.
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