Although morphine has been reported to inhibit VEGF expression in myocardial ischemia [26] and chronic morphine administration (10 mg kg−1, s.c.)for 6 days can provide relief from cancer pain and inhibit tumor growth and metastasis in a mouse model [27], so far no direct link between VEGF and morphine tolerance has ever been reported. The gene discussed is VEGFA; the disease is myocardial ischemia.