Besides its role in tumor cell growth, leptin has also been recognized as one of the most important mediators in cell-to-cell communication within the breast tumor microenvironment, mainly in the interaction between stromal cells (i.e., adipocytes, cancer-associated fibroblasts, endothelial cells, and macrophages) and neoplastic cells (as reviewed in [225]). The gene discussed is LEP; the disease is neoplasm.