This antibody labels the MutS homolog 6 (MSH6) protein in the nucleus of proliferating cells in both normal and neoplastic cells and does not label colon adenocarcinoma with complete loss of MSH6 expression. MSH6 is a useful tool for classifying tumors of the gastrointestinal tract, including associated extra colonic cancers such as endometrial and prostate cancers, when used in a panel of antibodies.