Genetic variations affecting some of the proteins that integrate the MMR system, including MLH1 (MutL homolog 1), MLH3 (MutL homolog 3), MSH2 (MutS homolog 2), and MSH3 (MutS homolog 3), are frequent in CRC and have been associated with its degree of chemoresistance. Here, MLH1 is linked to colorectal carcinoma.