LEP and obesity due to melanocortin 4 receptor deficiency: In addition, E0771 is the only mammary tumor cell line syngeneic to C57BL6 mice; thus, the model used is the indicated one for our studies in obesity and mammary cancer in the mouse, given that genetic models of obesity in mice, such as the ob/ob or db/db mice, deficient in leptin or its receptor respectively, are resistant to mammary cancer [37].