Systemic factors related to obesity, such as interleukin-6 receptor (IL-6R), leptin receptor (OB-R) and insulin-like growth factor-I receptor (IGF-IR), can inhibit the expression of ERβ in breast cancer cells through the pathway mediated by human epidermal growth factor receptor 2 (HER2) so that cancer cells can obtain greater cell activity, thus promoting their growth and worsening the prognosis of breast cancer (83). This evidence concerns the gene ERBB2 and obesity due to melanocortin 4 receptor deficiency.