AD 923 is an optimised, sublingual formulation of the strong opioid analgesic fentanyl. It has been specifically designed to provide rapid onset of analgesia in a device that is easy to use by either the patient suffering from cancer breakthrough pain or their care giver. An additional benefit is the lockout system that prevents inadvertent overdosage. Cancer breakthrough pain is characterised by temporary exacerbations of moderate to severe pain in cancer patients that "breakthrough" their around-the-clock opioid treatments. Each episode may be spontaneous or incidental to an activity. It is estimated that the condition is prevalent in approximately 60% of cancer pain patients across Europe, the US and Japan, representing a total population size of 2.3 million. Most current treatments for cancer breakthrough pain are considered sub-optimal. The market seeks products which have a rapid onset of action and are easy to use. The current worldwide market for cancer breakthrough pain drug treatment is estimated to be worth $1.5 billion and represents a growing market opportunity. Three Phase I studies have been completed. Data demonstrated rapid absorption and high bioavailability. In February 2008, Phase III trials investigating the efficacy and safety of AD 923 against an active comparator commenced in Europe. In June 2006 Sosei entered into an agreement with Mundipharma International Corporation Limited ("Mundipharma") for the development and commercialisation of AD 923 in Europe and other international markets, excluding North America and Japan. Three Phase I studies have been completed. Data demonstrated rapid absorption and high bioavailability. Also, a US Phase I study completed in May 2007 showed more rapid absorption, higher bioavailability and lower Tmax (time to maximum plasma concentration) compared with Actiq®. In February 2008, Phase III trials investigating the efficacy and safety of AD 923 against an active comparator commenced in Europe. However, due to a technical problem concerning a supplied component in the device used to deliver the fentanyl spray which could result in a sub-optimal dose of medication, Phase III was temporary halted in March 2008, as a precautionary measure to ensure patient safety.