Characterisation and Epidemiology of Breakthrough Cancer Pain in Spain

Inclusion Criteria: * Participants≥ 18 years old * Participants with baseline cancer pain that is adequately controlled with opioids * Presence of episodes of breakthrough pain associated with the cancer pain * Meeting the diagnostic criteria for breakthrough cancer pain (participant history and Portenoy's criteria) and the Davies algorithm * Participants who are not receiving treatment for breakthrough cancer pain. It is not permitted the inclusion of participants receiving treatment for breakthrough cancer pain in order to avoid bias that may affect the characterization or taxonomy of breakthrough cancer pain * Signing of the informed consent Exclusion Criteria: * Severe mental illness * Any medical condition or situation complicating the collection of study data as determined by the investigator