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