The finding of higher leptin binding activity (LBA) levels in homozygous carriers of the G allele (LEPR Arg223Arg) and higher levels of leptin in the LEPR Arg223Arg homozygotes and our finding of increased premenopausal breast cancer risk in women carrying the LEPR 223Arg allele provides supportive evidence for this proposition. This evidence concerns the gene LEP and breast cancer.