Our findings indicated a protective association between the PI3K rs121913281 CT genotype and breast cancer susceptibility in the codominant model, with an OR of 0.40 (95%) CI = 0.204–0.804, RR = 0.62 and p < 0.009 (Table 5), whereas the PI3K rs121913281 TT genotype was strongly linked to breast cancer susceptibility with an OR of 3.54, (95%) CI = 1.0544–11.896, RR = 2.62 and p < 0.040. The gene discussed is PIK3CA; the disease is breast cancer.