ESR1 and obesity due to melanocortin 4 receptor deficiency: Some studies claimed that there is a positive relationship between obesity and risk of BC in premenopausal ER-negative and TNBC since the ER−/PR− tumor is more common in obese women compared to the ER+/PR+ tumor [230], while other studies suggest that BMI is inversely associated with premenopausal ER+ BC [230,231].