LEP and breast cancer: Studies investigating the role of the leptin-axis manipulation on breast carcinogenesis using genetic loss-of-function or mutation or by dietary manipulation have demonstrated how the development of mammary cancers is dependent upon an intact leptin-axis as obese mice lacking leptin or leptin receptors did not develop tumors (Cleary et al., 2003; Cleary et al., 2004; Dogan et al., 2007).