The treatment of these two cell lines with leptin at 10 ng/mL and 100 ng/mL, concentrations that mimic plasma leptin levels in lean individuals and those with obesity [17], led to marked overexpression of LEPR in (the more aggressive cell line) MDA-MB-231 cells but not in MCF-7 cells. Here, LEP is linked to obesity due to melanocortin 4 receptor deficiency.