Given the recent evidence linking Mφ to induction of steroid receptor expression in hormone-responsive tumor types other than BC [43,44], we hypothesized that in obesity-associated BC, Mφ residing in the tumor microenvironment can regulate cellular levels of ER expressed by carcinoma cells, increasing their sensitivity to the hormone and, thus, contributing to enhanced estrogen signaling. The gene discussed is ESR1; the disease is obesity due to melanocortin 4 receptor deficiency.