The purpose of this study is to compare the safety and efficacy of Oral Osmotic Therapeutic System (OROS) hydromorphone hydrochloride (HCl) with controlled-release oxycodone HCl in participants with cancer-related pain.

This is a double-blind (a medical research study in which neither the researchers nor the participants know what treatment the participants is receiving), randomized (study drug is assigned by chance), multi-center (when more than one hospital or medical school team work on a medical research study), comparative, parallel-group (a clinical trial comparing the response in two or more groups of participants receiving different treatments) study of OROS hydromorphone HCl compared with oxycodone HCl controlled-release in participants with moderate to severe cancer (abnormal tissue that grows and spreads in the body until it kills) pain. The study will consist of 3 phases: a screening period (up to 14 days before randomization), a dose titration phase (up to 8 days), and a dose maintenance phase (28 days). The study visits will be scheduled at weekly intervals. Eligible participants will be randomly assigned to receive either hydromorphone HCl once daily or oxycodone HCl twice daily (placebo will be administered when necessary for blinding). During titration phase, dosage of hydromorphone HCl or oxycodone HCl will be adjusted upward or downward to achieve stable pain control. It can be from 2 days to 8 days. Participants who complete dose titration will enter into the dose maintenance phase and will receive study treatment for 28 consecutive days. Morphine hydrochloride will be given as rescue analgesic (drug used to control pain) medication for breakthrough pain during the study. Primarily efficacy will be evaluated by measuring change in the score of Brief Pain Inventory (BPI) questionnaire item 'worst pain' at end of maintenance period. Participants' safety will be monitored throughout the study.

Inclusion Criteria:

• Participants receiving strong oral or transdermal (through the skin) opioid analgesics with inadequate control of moderate to severe (very serious, life threatening) cancer pain or who presented with cancer pain and will be eligible to move to Step 3 of the WHO analgesic ladder when receiving weak opioids
• Participants who require or are expected to require between 40 mg and 184 mg of oral morphine or morphine equivalents every 24 hours for the chronic management of cancer pain
• Participants who are reasonably expected to achieve a stable dose of opioid study medication during the study
• Participants who are not expected to start a course of chemotherapy, radiotherapy, targeted cancer therapy, hormone therapy or diphosphates therapy after enrolment into the study. If participants are receiving long-term treatment including hormone therapy, target cancer therapy and diphosphate, the treatment should be kept stable as much as possible from 2 weeks before randomization and up to the completion of the study, encompassing the titration and maintenance phases
• Female participants who are premenarchal, postmenopausal, or surgically sterile, abstinent or if sexually active, they must use a medically acceptable method of contraception and must be willing to continue to use the same method of contraception throughout the study

Exclusion Criteria:

• Participants with neuropathic pain or pain of unknown origin, or acute pain - Participants having pain only on movements
• Participants requiring other opioid analgesics (apart from morphine hydrochloride (HCl), in immediate release formulation, allowed as rescue medication for breakthrough pain)
• Participants with a recent history (within the previous 6 months) or current history of drug abuse or alcohol abuse
• Women of childbearing potential who were pregnant or lactating, seeking pregnancy or failing to use an adequate contraceptive method