Methadone Hydrochloride as First-Line Therapy in Treating Patients With Chronic Neuropathic Cancer Pain

DISEASE CHARACTERISTICS: * Patients diagnosed with cancer and experiencing chronic neuropathic pain syndrome * Pain syndrome diagnosed by the investigator * Pain syndrome related to the effects of cancer or its treatment (i.e., chemotherapy, radiotherapy, and surgery) * Meets 1 of the following criteria: * Need to be started on strong opioids * Require an increase in opioid dose and are currently taking ≤ 75 mg of total daily dose of oral morphine equivalent * Experiencing pain for ≥ 4 weeks with an average pain score of ≥ 4 or a worst pain score of ≥ 5 (using the 0-10 Brief Pain Inventory Scale) during the past 24 hours * Requires strong opioids to control pain and is using an oral morphine-equivalent dose of 0-75 mg per day, on average, including breakthrough analgesia, within the past 3 full calendar days * Mixed pain syndrome allowed provided the neuropathic component is the predominant pain * Meets 1 of the following criteria: * Receiving concurrent chemotherapy but the chronic neuropathic pain is not related to this treatment and is not expected to improve or worsen because of this therapy * Received prior chemotherapy but discontinued treatment, has not received chemotherapy within the past 7 days, and no further chemotherapy is planned * No prior chemotherapy PATIENT CHARACTERISTICS: * Karnofsky performance status 40-100% * ALT and AST ≤ 3 times upper limit of normal (ULN) * Creatinine ≤ 2 times ULN * No other known laboratory abnormality tha…