ESR1 and obesity due to melanocortin 4 receptor deficiency: Moreover, the oxysterol; 27-hydroxycholesterol, a cholesterol metabolite and an endogenous selective estrogen receptor modulator capable of promoting the autonomous growth of ER positive breast cancer [7, 23, 24], is thought to be the biochemical link between the elevated risk of ER positive breast cancers in women with obesity and/or hypercholesterolemia [7].