DISEASE CHARACTERISTICS: Chronic visceral or somatic pain due to cancer or prior cancer therapy No pain primarily classified as neuropathic or unknown in nature Required opioid analgesic at least 5 days/week for at least 2 weeks prior to study Expectation of continued requirement for daily opioid medication (morphine sulfate, oxycodone, or hydromorphone)

PATIENT CHARACTERISTICS: Age: Legal age and over Performance status: Karnofsky 60-100% Life expectancy: At least 4 months Hematopoietic: Platelet count at least 40,000/mm3 No platelet function disorder Hepatic: No known significant hepatic insufficiency Renal: Creatinine less than 1.5 mg/dL BUN less than 1.5 times upper limit of normal Creatinine clearance greater than 50 mL/min No known renal insufficiency Gastrointestinal: No diagnosis of esophageal, gastric, pyloric channel, or duodenal ulceration within the past 30 days No history of esophageal or gastric cancer No intractable nausea or vomiting No inability to swallow tablets or to tolerate oral medication Other: Weight at least 50 kg No AIDS or AIDS-related cancers No history of hypersensitivity to cyclooxygenase inhibitors (e.g., NSAIDs or specific COX-2 inhibitors) or opiates No significant alcohol, analgesic, or narcotic substance abuse within the past 6 months No history of unstable disease or condition that would preclude study Not pregnant or nursing Negative pregnancy test Fertile patients must use effective contraception

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: At least 3 weeks since initiation of new chemotherapy agent No concurrent participation in an investigational chemotherapy trial Endocrine therapy: At least 2 weeks since initiation of corticosteroids as an analgesic adjuvant Radiotherapy: At least 4 weeks since prior radiopharmaceutical therapy or radiotherapy No concurrent radiopharmaceutical therapy or radiotherapy Surgery: No concurrent therapeutic procedure (e.g., surgery or biopsy) that would affect pain intensity Other: No prior participation on this study At least 30 days since prior investigational agent At least 30 days since prior treatment for esophageal, gastric, pyloric channel, or duodenal ulcer At least 8 weeks since initiation of bisphosphonates At least 2 weeks since anticancer therapy that would affect study evaluation At least 2 weeks since initiation of antidepressants, anti-epilepsy drugs, or antihistamines as an analgesic adjuvant At least 5 half-lives since prior specific COX-2 inhibitors or non-steroidal anti-inflammatory drugs (NSAIDs) No concurrent other investigational agent No concurrent anticancer therapy that would affect study evaluation No concurrent other analgesics, specific COX-2 inhibitors, or NSAIDs except as specifically permitted on study Concurrent acetaminophen less than 2 g/day allowed if given 2 days or fewer per week Concurrent acetylsalicylic acid no greater than 325 mg/day allowed