Dexmedetomidine Addition to Morphine in Patients With Metastatic Cancer

Inclusion Criteria: * Any painful patient with metastatic cancer * Whatever type of pain: nociceptive, neuropathic, or mixed * Age \> 18 and \<75 years * Patient under analgesic Tier III treatment: with moderate to severe pain and not relieved by non-opioid conventional treatment * Patient cooperating capable of responding to the pain assessment by providing a number from 0 to 10 at the VAS * Patient providing his explicit consent to participate in the study before inclusion (regardless of his inclusion in C or D Group) * Patients with systolic blood pressure (SBP) ≥ 100 mmHg and a diastolic blood pressure (DBP) ≥ 50 mmHg * Patients with a heart rate ≥ 50/min Exclusion Criteria: * Patient refusal to participate in the study or patient unable to give consent * Age \<18 or \> 75 years * Comatose uncooperative patient unable to respond to the assessment of pain by VAS * Hypotensive patients with SBP \< 100 mmHg and DBP \< 60 mmHg or bradycardic with a heart rate \< 50/min * Patient with a heart rhythm disorder, or a disorder of the atrial-ventricular conduction * Patients under beta-blocker * Patient with heart failure with an ejection fraction \< 40% * Patient suffering from allergy or previous intolerance to morphine or dexmedetomidine * Patient with renal impairment with a creatinine clearance \<3 0ml/min/1.73m2, or patient under hemodialysis or peritoneal dialysis. * Patient with severe hepatic impairment with Child-Pugh score at C.