Fig. 2

A mismatch repair-deficient adenocarcinoma of the sigmoid colon was originally interpreted to show retained mismatch repair protein staining. Non-neoplastic colonic mucosa and lymphoid aggregate (a) show diffuse strong nuclear staining for MLH1 (c) and PMS2 (e). In comparison, tumor cells (b) show positive but reduced and heterogeneous staining of both MLH1 (d) and PMS2 (f)