Source:http://linkedlifedata.com/resource/umls/id/C1135120
NCI: Intense increases in pain that occur with rapid onset even when pain-control medication is being used. Breakthrough pain can occur spontaneously or in relation to a specific activity.,MSH: Acute pain that comes on rapidly despite the use of pain medication.,NCI: Many people with chronic cancer-related pain experience intermittent flares of pain that can occur even though a person is taking analgesic medications on a fixed schedule for pain control. These severe flares of pain are called breakthrough pain because the pain "breaks through" the regular pain medication.