MIB-1 and MCM-2 immunohistochemical analysis does not aid in identification of serrated colorectal polyps with abnormal proliferation.

We investigated the staining characteristics of serrated polyps with abnormal proliferation (SPAP) using MIB-1 and MCM-2 to determine if they could provide assistance in delineating SPAPs from traditional hyperplastic polyps (HPs). Using published morphologic criteria we reviewed H&E slides of 107 polyps from 80 patients. Thirty-nine (36.4%) polyps met the criteria for SPAP Within a given region, polyps in the transverse colon had the largest percentage of SPAPs (50.0%) followed by the right colon (40.9%). The majority of SPAPs (82.1%) and HPs (72.1%) showed MIB-1 staining confined to the basal third of the crypts. The majority of SPAPs (59.0%) and HPs (52.9%) showed MCM-2 staining extending into the apical third of the crypts. We do not recommend MIB-1 or MCM-2 staining to differentiate SPAPs from conventional HPs, since staining characteristics are not significantly different between the 2 groups, and frequent variable crypt staining within a given polyp is difficult to interpret.