LEP and breast cancer: The aforementioned has been observed in diverse in vitro experiments, in which the promoting activity of proliferation in breast cancer cell lines by leptin is mediated through different signal pathways; on one hand, it acts by inducing the P13K/Akt survival pathway, activating the phosphorylation of Akt, stimulating protein expression of PKC-alpha, activating the MAPK pathway, and stimulating ERK1 and ERK2 [17–20].