CYP3A4 and obesity due to melanocortin 4 receptor deficiency: Considering the aforementioned reasons, including limited previous research, inconsistent research results, and the lack of interaction analysis between CYP3A4 gene and obesity, we therefore performed this study to evaluate the relationship between four single nucleotide polymorphisms (SNPs) of CYP3A4 gene and susceptibility to breast cancer, and the impact of SNP-SNP and gene-obesity interactions on breast cancer susceptibility in Chinese women.