Eligible patients who agree to participate will migrate from oral opioids to transdermal patches and be followed for four weeks. Oral morphine will be provided as pain rescue medication. The patients will inform the adverse events and rescue medication consumption. The number of Fentanest® patches will be adjusted every visit aiming to reduce the rescue medication consumption and adverse events to a minimum. The WHO-QOL- bref (quality of life questionary) will be filled before and after the use of Fentanest®. Patients showing benefit are eligible to a 3 weeks compassionate study.

Inclusion Criteria:

• Male or female outpatients aged from 18 to 70 years with cancer chronic pain who received in the last 4 weeks at least 40 mg of oral morphine or equianalgesic dose of other opioids. If using adjuvant analgesics, these must be in stable doses in the last 4 weeks.

Exclusion Criteria:

• Life expectancy bellow 4 months;
• Karnofsky score < 60;
• Hypersensitivity to opioids or patches;
• Acute pain;
• Non cancer pain;
• Increased intracranial pressure;
• Conditions that prevent the patient to understand the study directions and/or give his consent;
• Neuromuscular disorders with increased risk of respiratory depression;
• Impossibility to receive rescue oral morphine; active infections;
• Fever;
• Pregnancy and nursing;
• Uncontrolled diabetes mellitus or arterial hypertension;
• Need of anticoagulation;
• Need to operate machines or vehicles;
• Important skin disorders;
• History of severe allergic reactions;
• BMI ≥ 35;
• Safety exams outrange;
• Participation in another clinical trial within the last 2 months;
• Investigator´s opinion.