Mismatch repair proteins are nuclear enzymes which participate in repair of mismatch errors during DNA replication. Loss of Mismatch repair proteins increases the number of DNA replication errors in the proliferating cells. Errors occur especially in areas of the genome with short repetitive nucleotide sequences - causing microsatellite instability (MSI). MSH6 is a mismatch repair protein which is not expressed in a high proportion of patients with MSI-H. MSH6 antibody can be useful for immunohistochemical analyses of MSH6 protein in neoplastic tissues and identification of loss of MSH6. Immunohistochemical analysis of MSH6 should be performed in IHC panel together with MLH1, MSH2 and PMS2.