When evaluating by gene, only two of the four MMR genes were found to have a statistically significant increased association with breast cancer: MSH6 (SIR = 2.11; 95% CI, 1.56–2.86) and PMS2 (SIR = 2.92; 95% CI, 2.17–3.92). This evidence concerns the gene MRC1 and breast carcinoma.