['Our objective was to evaluate the MTHFR C677T-A1298C polymorphisms in patients with breast cancer and in individuals with no history of cancer, to compare the levels of genetic damage and apoptosis under folic acid (FA) deficiency between patients and controls, and to assess associations with breast cancer.', 'Genetic damage was marked by micronucleated binucleated cells (MNBN) and apoptosis was estimated by cytokinesis-block micronucleus assay (CBMN). PCR-RFLP molecular analysis was carried out.', 'The results showed significant associations between the MTHFR 677TT or the combined MTHFR C677T-A1298C and breast cancer risk (OR=2.51, CI=0.85 to 7.37, p=0.08; OR=4.11, CI=0.78 to 21.8, p<0.001). The MNBN from the combined MTHFR C677T-A1298C was higher and the apoptosis was lower than that of the single variants (p<0.05). At 15 to 60 nmol /L FA, the MNBN in cases with the TTAC genotype was higher than controls (p<0.05), whereas no significant difference in apoptosis was found between the cases and controls after excluding the genetic background.'] Do interactions between MTHFR C677T-A1298C variants and folic acid deficiency affect breast cancer risk in a Chinese population?