An elevated BMI is associated primarily with postmenopausal, ER+ breast cancer [31] but is protective in premenopausal breast cancer [31] with one critical exception: visceral adipose tissue accumulation in premenopausal breast cancer is a risk factor for triple negative breast cancer (TNBC) [6,8,9,10,11] and HER2+ER− [8]. This evidence concerns the gene ESR1 and breast cancer.