LEP and obesity due to melanocortin 4 receptor deficiency: Furthermore, different doses of leptin (10 ng/mL, 100 ng/mL and 1000 ng/mL) have been administrated to the 184B5 normal breast cell line and to the MCF-7, MDA-MB-231, and T47D BC cell lines, showing that leptin stimulates the proliferation of cancer cells but not of normal breast cells, further supporting the possibility that hyperleptinemia represents an effector through which obesity contributes to BC development [120].