Methadone, Morphine, or Oxycodone in Treating Pain in Patients With Cancer

DISEASE CHARACTERISTICS: * Receiving ongoing care in the outpatient medical oncology setting * Self-reported pain (of any cause) for which long-acting strong opioids (morphine or oxycodone) have been prescribed or administered * Oral morphine-equivalent daily dose (MEDD) of existing opioid regimen (long-acting or immediate-release) 40-300 mg/day * Worst pain score on a scale of 0 (no pain) to 10 (worst pain) of ≥ 5 for ≥ 1 week duration based on verbal self-report AND/OR ≥ 1 persistently bothersome symptom attributed to an opioid side effect (e.g., fatigue, confusion, depressed level of consciousness, memory loss, personality change, anorexia, constipation, dehydration, nausea, vomiting, weight loss, pruritus, urticaria, impotence, reduced libido, and urinary retention or hesitancy) PATIENT CHARACTERISTICS: * None of the following conditions that could predispose the patient to prolonged QT interval-associated tachycardia: * Serum potassium \< 3.0 mg/dL * Cocaine abuse within the past 3 months * Family history of sudden death * Advanced heart failure (ejection fraction \< 40% and/or New York Heart Association (NYHA) class III or IV heart disease) * No known or suspected cognitive impairment that could interfere with adherence to the medication plan or self-report of symptoms and side effects * Not pregnant or nursing * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: * See Disease Characteristics * More than 4 weeks since prior radi…