RESUMEN
Immunohistochemical decrease in staining for mismatch repair proteins may be seen in either microsatellite instability or inactivation (methylation) of mismatch repair proteins. Both are features of the malignant phenotype in a range of colorectal neoplasms. Expression of mismatch repair proteins in dysplastic lesions in ulcerative colitis (UC) has not been studied extensively. The authors analyzed protein expression of hMLH1, hMSH2, and hMSH6 in 18 cases of dysplasia-associated lesion or mass (DALM) in patients with UC and 10 sporadic adenomas. Immunohistochemical studies revealed adequate staining in almost all of the cases. A significant decrease in protein expression was seen in 2 DALM and 2 sporadic adenomas. The authors conclude that immunohistochemical studies of mismatch repair proteins can be applied to dysplastic lesions in UC with adequate staining results. Decreased wild type expression of hMLH1, hMSH2, and hMSH6 is not a feature of DALM in the setting of UC.