ESR1 and obesity due to melanocortin 4 receptor deficiency: Obesity promotes the secretion of proinflammatory cytokines, resulting in inflammation.26 An experimental study reported that interleukin (IL)-6 derived from adipose stromal cells stimulates migration and invasion of malignant breast cells.27 In addition, this study showed that adipocytes promote the invasive capacity of cancer cells in ER− and ER+ breast cancer, indicating that this mechanism is independent of the hormonal function of adipose tissue.