In the premenopausal group, women carrying the AA genotype were found to have a significantly reduced risk of breast cancer (OR = 0.56, 95% CI 0.34–0.94, p = 0.027), and we found a significant association between MPO G-463A polymorphism and breast cancer risk with the recessive model (OR = 0.57, 95% CI 0.34–0.93, p = 0.025) (Table 5, Figure 2). This evidence concerns the gene MPO and breast cancer.