However, since there is a scarcity of data about the involvement of polymorphisms in other MMR genes in breast cancer susceptibility, we carried out a hospital-based case-control study in a Caucasian Portuguese population to estimate the potential modifying role of the MSH3, MSH4, MSH6, MLH1, MLH3, PMS1 and MUTYH gene polymorphisms on the individual susceptibility to breast cancer. The gene discussed is MLH1; the disease is breast cancer.