Moreover, the action of morphine on specific tumor expressed classical GPCRs (μ, κ, and δ opioid receptors) can activate the MAPK/ERK or Akt/MTOR signaling pathways, and thus can simultaneously transactivate vascular endothelial growth factor to induce tumor angiogenesis and promote tumor cell proliferation23. The gene discussed is VEGFA; the disease is neoplasm.