CYP19A1 and obesity due to melanocortin 4 receptor deficiency: There are several ongoing initiatives related to estrogen levels in patients with breast cancer and obesity, ie, studies by Wellberg et al35,57,58 on the role of estrogen in preclinical obese breast cancer models and clinical studies by Iyengar et al.59 investigating the effect of exercise and plant-based diet on aromatase levels in postmenopausal women with obesity and HR+ breast cancer.