IRS1 and obesity due to melanocortin 4 receptor deficiency: Seven candidate genes were chosen for inclusion in this study: ADRB2, ADRB3, GHRL, HSD11B1, IRS1, IRS2, and SHC1. Although many more genes are related to obesity and energy balance, we chose candidate genes that had previously been associated with at least one measure of obesity and with risk for breast cancer [6-10] or other cancer [11,12], or had demonstrated activity in breast cancer cell lines [13-15].