Finally, 55 studies were meta-analyzed for the association between 5 genetic alterations in 3 genes (LEP, leptin receptor [LEPR] and ADIPOQ) and breast cancer risk, 4 studies for the association between rs7799039 genotypes and circulating leptin levels, and 8 studies for the association between rs1137101 genotypes and circulating leptin levels. This evidence concerns the gene LEP and breast cancer.