However, in a large series of unselected colorectal carcinomas, evidence of primary alteration of PMS2 (i.e., immunohistochemical findings of isolated loss of PMS2 protein expression with normal expression of its heterodimeric partner MLH1 and of the other MMR proteins) was approximately as common as loss of MSH2 (Truninger et al., 2005). This evidence concerns the gene PMS2 and colorectal carcinoma.