CYP19A1 and obesity due to melanocortin 4 receptor deficiency: For postmenopausal breast cancer, this might be explained by the high circulating estrogen levels in obese women which are produced by aromatase in adipose tissue.24 In premenopausal obese women, circulating levels of total IGF-I were associated with a higher risk of breast cancer.25 Moreover, long-standing hyperinsulinemia, which is seen in obesity, promotes tumorigenesis in estrogen-sensitive tissues.26 Adiponectin is an adipokine that is inversely correlated with BMI.