Although opioid rotation is well known treatment modality in reducing pain and opioid-induced neurotoxicity, it is not established whether opioid rotation is more appropriate or opioid escalation is more effective in controlling significant pain in cancer patients under opioid medication.

- The purpose of this study is to determine effective therapy out of opioid rotation and opioid dose escalation in patients with moderate to severe cancer pain who have been already treated with strong opioid.

Inclusion Criteria:

• age > 18 years
• patients who are being treated with one of strong opioids including oral oxycodone, oral hydromorphone, or fentanyl patch with range from 60 mg to 200 mg of oral morphine equivalent daily dose (MEDD)
• moderate to severe cancer pain (numeric rating scale more than 3) at screening
• patients without uncontrolled adverse effects associated with currently applied opioid

Exclusion Criteria:

• previous opioid rotation
• unable to take oral medication
• life expectancy less than a month
• newly started chemotherapy and/or radiotherapy within past 2 weeks of screening
• serum aspartate aminotransferase, alanine aminotransferase, or alkaline phosphatase > 2.5 times of upper normal limit
• serum total bilirubin or creatinine > 1.5 times of upper normal limit