¹⁸F-FDG PET/CT Versus Diagnostic Contrast-Enhanced CT for Follow-up of Stage IV Melanoma Patients Treated by Tyrosine Kinase or Immune Checkpoint Inhibitors: Frequency and Management of Discordances Over a 3-Year Period in a University Hospital

Aim To perform a comprehensive analysis of discordances between contrast-enhanced CT (ceCT) and 18F-FDG PET/CT in the evaluation of the extra-cerebral treatment monitoring in patients with stage IV melanoma. Materials and methods We conducted a retrospective monocentric observational study over a 3 years period in patients referred for 18F-FDG PET/CT and ceCT in the framework of therapy monitoring of immune checkpoint or tyrosine kinase inhibitors (ICIs or TKIs) as of January-2017. Imaging reports were analysed by two physicians in consensus. Anatomical site responsible for discordances, as well as induced changes in treatment were noted. Results Eighty patients were included and 195 couples of scans analysed. Overall, discordances occurred in 65 cases (33%). Eighty percent of the discordances (52/65) were due to 18F-FDG PET/CT scans upstaging the patient. Amongst these discordances, 17/52 (33%) led to change in patient’s management, the most frequent being radiotherapy of a progressing site. ceCT represented 13/65 (20%) of discordances and induced changes in patients’ management in 2/13 cases (15%). The more frequent anatomical site involved was subcutaneous for 18F-FDG PET/CT findings and lung or liver for ceCT. Conclusions Treatment monitoring with 18F-FDG