LEP and obesity due to melanocortin 4 receptor deficiency: To further establish leptin’s role in obesity-induced BC progression, we compared the effects of a high leptin dose (100 ng/mL), which mimics leptin plasma levels in individuals with obesity [13], with those of a low dose (10 ng/mL), commonly seen in lean individuals [17], on the activities of MCF-7 and MDA-MB-231 cells.