After adjusting for oral contraceptive use and family history of breast cancer, the presence of the G allele and the GG (AG + GG) genotype of the CYP3A4*1B polymorphism was not directly associated with tumor occurrence (OR = 1.151; 95%CI: 0.714–1.856; p = 0.564). Here, CYP3A4 is linked to breast cancer.