The patients will receive only one dose treatment of Tramadol hydrochloride/Acetaminophen oral tablets throughout the study. The number of oral tablets be given will be depend on the total daily dose of around-clock medications. If around-clock medication is Tramadol <=400mg or codeine <=300mg or morphine <60mg, the breakthrough pain medication will be 1 tablet. If around-clock medication is morphine 60-120mg or Fentanyl >=25 ug/hr, the breakthrough pain medication will be 2 tablets.