This 2019 review article, published in International Immunopharmacology, examines the role of the opioid growth factor (OGF)–OGF receptor (OGFr) axis in cancer therapy. OGF, identified as [Met5]-enkephalin, is an endogenous peptide that binds to OGFr to regulate cell proliferation by inhibiting DNA synthesis. The review discusses how low-dose naltrexone (LDN),
