MTHFR and diabetes mellitus: To understand the association between the MTHFR C677T polymorphism and the clinical features of the 4 subtypes of BCs, logistic regression analysis was used to evaluate the association between the MTHFR C677T polymorphism and clinical characteristics (age at diagnosis and menarche, diabetes mellitus, presence of hypertension, cancer family history, menopause, BMI, tumor size, LNM stage, distant metastasis and tumor stage classification), as shown in Table 3.