Melatonin inhibits tumor growth by suppressing the actions of prolactin-insulin-like growth factor-1 (IGF-1), growth hormone-dependent growth factors (GHFs), epidermal growth factor receptor (EGFR), vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), transforming growth factor (TGF), and platelet-derived growth factors (PDGF). The gene discussed is IGF1; the disease is neoplasm.