Inclusion Criteria:

• Pain due to cancer or its treatment; controlled baseline pain;
• episodes of breakthrough pain every day that are "4/10" in severity or greater, ;
• ast 10 minutes or longer, and
• are responsive to short acting oral opioids such as morphine or hydromorphone;
• are able to hole a volume of 1.0cc of water under the tongue for a 5-minute period; are able to provide written informed consent;
• are able to fill out the study forms

Exclusion Criteria:

• Severe underlying respiratory disease such that an investigator is wary about the risk of respiratory failure from modest doses of opioid;
• prior sensitivity to methadone;
• currently are being administered methadone;
• have breakthrough pain that in the opinion of the investigator is likely to change within the next seven days (recent or imminent radiation therapy to the main site of pain,
• new chemotherapy or use of an injectable bisphosphonate likely to alter the pain, new use corticosteroids within the past week with a corresponding change in pain, or other interventions judged likely to alter pain);
• are clinically unstable or have a life expectancy of less than one month making completion of the trial unlikely