ESR1 and obesity due to melanocortin 4 receptor deficiency: For instance, among premenopausal women, obesity is associated with lower risk of hormone receptor-positive (estrogen receptor (ER)+ and progesterone receptor (PR)+) breast cancer, but higher risk of hormone receptor-negative breast cancer [18,19]; whereas among postmenopausal women, obesity is associated with higher risk of hormone receptor-positive breast cancer [20].