Effectiveness and Tolerance of Fentanyl Citrate in Painful Pain Induced During Diagnostic or Therapeutic Examinations in Cancer Patients

Inclusion Criteria: 1. Age ≥18 years. 2. Patients in follow up or being treated for cancer. 3. Patients with cancer-related pain (area of pain located near primary tumor or metastatic lesions). 4. Patients: 1. not having received any opioid treatment (opioid naïve). 2. or, treated for less than 7 days by a slow-releasing/extend-release opioid treatment; and/or by less than 60 mg per day of oral morphine, or less than 30 mg/day of oral oxycodone, or less than 8 mg/day of oral hydromorphone, or less than 25 µg/h of transdermal fentanyl. 5. Patients need to have at least one of the following interventions, lasting between 25 and 45 minutes during which they will be request to not move: 1. Radiotherapy session\*, including tomography (patients hospitalized or treated as outpatients). 2. Dosimetric scanner (hospitalized patients). 3. Positron-emission tomography\*\* (PET): PET-computed tomography \[CT\] scan and single photon emission computed tomography \[SPECT\]-CT scan (hospitalized patients). 6. Public health insurance coverage. (\*) A patient who has numerous radiotherapy sessions can only be included once; (\*\*) with acquisition phase in a prostrate or decubitus dorsal position and strictly immobile in one of the cameras (PET or SPECT). Inclusion criteria (cohort): As for the inclusion criteria for the phase II study, with the following modifications: 4\. Patients treated with a slow-releasing/extended-release opioid for: 1. more than 7 days. 2. and with at least 60 mg per day of oral morphine, or at least 30 mg/day of oral oxycodone, or at least 8 mg/day of oral hydromorphone, or at least 25 µg/h of transdermal fentanyl. 5\. Patients who believes that they are cannot assume a prostrate or decubitus dorsal position for a diagnostic or therapeutic examination/intervention due to the pain they will experienced in this position, Or Patients experience breakthrough pain (numerical pain scale 5), in a region corresponding to the localization of the metastatic lesions or the primary tumor, when they assume a prostrate/decubitus dorsal position, Or Patients who have breakthrough pain (numerical pain scale 5) in a region corresponding to the localization of the metastatic lesions or the primary tumor that prevents the completion of a diagnostic or therapeutic examination/intervention. 6\. Public health insurance coverage. Exclusion Criteria: 1. Patients with contraindication for the administration of fentanyl citrate: severe respiratory depression or a severe obstructive pulmonary disease. 2. Patients who have already participated in this study. 3. Patients with a history of alcoholism or substance/drug dependence. 4. Patients with an intravenous or subcutaneous opioid patient-controlled analgesic (PCA) pump. 5. Patients unable to communicate or understand instructions in French. 6. Patients deprived of their liberty or under protective custody or guardianship, or unable to provide their consent for study participation. 7. Patients who are pregnant or breast-feeding.