In postmenopausal women with obesity, the higher risk of estrogen receptor (ER)-positive BC is known, but similarly, increased adiposity in postmenopausal women with a normal body mass index also pose them at double risk of invasive BC (HR 2.21, 95% CI, 1.23–3.67). The gene discussed is ESR1; the disease is obesity due to melanocortin 4 receptor deficiency.