While it has been hypothesized that the observed decrease in treatment efficacy of aromatase inhibitors in women with obesity could be due to an inadequate suppression of aromatase within adipose tissue [46], pre-clinical models have also suggested that alterations in the stroma within and surrounding breast tumors may also impact responsiveness [47, 48]. The gene discussed is CYP19A1; the disease is obesity due to melanocortin 4 receptor deficiency.