MLH1 and mismatch repair cancer syndrome 1: The mechanism of carcinogenesis resulting from inherited MMR deficiency has been well studied, particularly in colorectal cancer [4,27], and has been modeled in cell line systems such as HCT-116 O cells, which are MLH1-deficient but contain an extra copy of Chromosome 2, and HCT-116 N cells, in which the MLH1 deficiency is complemented by an extra copy of Chromosome 3 that contains wild type MLH1 [28].