LEP and breast cancer: Based on the reported leptin-mediated overexpression of aromatase [18] and transactivation of ER [19] in MCF-7 cells, we hypothesized that the effects of pegylated leptin peptide receptor antagonist 2 (PEG-LPrA2) on the growth of human BC xenografts will be more evident in MCF-7 ER+ BC than in MDA-MB231 ER- BC.