Breakthrough pain (BP) is a common problem in patients with cancer and is associated with significant morbidity in this group of patients. BP has been defined as a transitory increase in pain intensity that occurs either spontaneously, or in relation to a specific predictable or unpredictable trigger, despite relatively stable and adequately controlled background pain. A well understood subtype of BP is incident pain, which is due to movement and commonly associated with bone metastases or fractures. These episodes are associated with a functional impairment on measures of mood and anxiety, and on scales of pain interferences with function. A comprehensive pain assessment is recommended including frequency and duration of each episode, intensity, precipitating factors, previous and current pain treatments for baseline (persistent) pain, and their effectiveness. Onset and peak intensity, location, quality and predictability, and factors that precipitated them or provided relief once they occurred, or able to prevent them should also be recorded (by the patient). Given that different subtypes of BP exist, different therapeutic approaches are individually required, optimizing or assembling pre-emptive drugs for the prevention of the events. The availability of supplemental doses of oral opioids in addition to the continuous analgesic medication is the main treatment suggested to manage pain flares. An oral dose form can take a longer time to relieve pain, with peak concentrations achieved within 30-45 minutes. As pain relief is usually required urgently, therefore, routes of administration designed to deliver drugs rapidly are often chosen. Studies of oral transmucosal fentanyl citrate (OTFC) have shown that this approach produces a faster onset of relief and a greater degree of pain relief than the oral morphine, at 15, 30, and 60 min. The choice of the opioid dose to be prescribed as needed remains controversial. New delivery systems have been developed, including the effervescent technology to provide faster pain relief. Sublingual and intranasal administration of fentanyl will soon be introduced in the market to provide fast delivery of fentanyl.