According to previous reports, [39,40], a wide variety of synthetic and natural opioids, including those specific for μ (DAMGO, endomorphin-1 and -2), δ (DPDPE) and κ (U69593) opioid receptors, showed that none of these compounds had any effect on growth of ovarian cancer cell, except for opioid growth factor (OGF), endogenous opioid peptide. The gene discussed is PENK; the disease is ovarian carcinoma.