Breakthrough cancer pain (BCP) is common in patients with cancer, causing a negative impairment in quality of life. Recent diagnostic criteria allow for differentiation of background chronic pain and BCP, for which proportion of unpredictable episodes is very high. Five characteristics define BCP: rapid onset, high intensity, maximum intensity (minutes), mean duration 30 min, and unpredictable onset. Fentanyl is a synthetic opioid characterized by rapid absorption and start of the analgesic effects. In addition to comparing some of the marked differences between the four pharmaceutical forms of fentanyl marketed in Spain, this paper discusses the data collected in a comprehensive clinical trial program with fentanyl pectin nasal spray (FPNS), a formulation that takes advantage of the intranasal route and the PecSys™ technology. The FPNS formulation achieves analgesic action 5 min after application and significant pain relief at 10 min. FPNS, therefore, has key features to be an optimal treatment for BCP.