From each study, findings were categorized as “tumor growth,” “tumor death,” or “no effect.” A given study could report multiple findings, for instance, morphine (μOR agonist) could be found to stimulate cancer cell proliferation in a breast cancer cell line, while naloxone (a μOR antagonist) may be found to induce cancer cell apoptosis. The gene discussed is OPRM1; the disease is breast carcinoma.