MOR is highly expressed in human non-small cell lung cancer (NSCLC) tumor tissues, and the MOR agonist morphine increases Lewis lung carcinoma (LLC) cell proliferation, while MOR knockout mice or the opioid antagonist MNTX infusion attenuates LLC tumor growth and reduces lung metastasis (Mathew et al., 2011). Here, OPRM1 is linked to neoplasm.