MSH6 is a mismatch repair gene which is deficient in a high proportion of patients with microsatellite instability (MSI-H). This finding is associated with the autosomal dominant condition known as Hereditary Non-Polyposis Colon Cancer (HNPCC). The anti-MSH6 antibody is useful in screening patients and families for this condition. Colon cancers that are microsatellite unstable have a better prognosis than their microsatellite stable counterparts.