LEP and breast cancer: Some reports suggested a negative correlation between leptin and breast cancer in the premenopausal but not postmenopausal group (Petridou et al, 2000), whereas several authors described that there was no significant association between circulating leptin and breast cancer risk (Mantzoros et al, 1999; Coskun et al, 2003; Sauter et al, 2004; Stattin et al, 2004; Woo et al, 2006).