Fig. 4

Immunohistochemical examination of mismatch repair proteins shows lack of MLH1 (a) and PMS2 (b) expression in tumor nuclei, in contrast to the positive staining for MSH2 (c) and MSH6 (d). This evidence indicates that the tumor was an MSI-H CRC due to MLH1 functional abnormality. Intact nuclear staining in the stromal lymphocytes or adjacent normal epithelia was used as the internal positive control for mismatch repair proteins