Impact and diagnostic accuracy of 18F-FDG PET/CT in malignant melanoma staging and restaging: First Tunisian clinical report

<ns3:p> Background Accurate staging guides melanoma treatment. Conventional imaging modalities like contrast-enhanced CT (CECT) is widely used but relies on morphology which may miss early spread. 18F-fluorodeoxyglucose positron emission tomography/computed tomography ( <ns3:sup>18</ns3:sup> F-FDG PET/CT) combines metabolic and anatomic data and may improve detection. Methods We conducted a single-centre retrospective diagnostic accuracy study at a tertiary university hospital in Tunisia (December 2019-February 2024). All adults with histologically confirmed melanoma undergoing whole body <ns3:sup>18</ns3:sup> F-FDG PET/CT as well as CECT for initial staging or restaging were included. The reference standard was histopathology, otherwise composite verification with clinical/imaging follow-up ≥6 months. Outcomes were per-patient sensitivity, specificity, predictive values, and accuracy, inter-modality agreement (Cohen’s κ), and management change attributable to <ns3:sup>18</ns3:sup> F-FDG PET/CT. Results Of 51 screened, 35 patients were included (23 staging and 12 restaging). Compared with CECT, <ns3:sup>18</ns3:sup> F-FDG PET/CT reclassified stage in 22/35 (62.9%), upstaging 14 (40.0%) and downstaging 8 (22.9%). For nodal disease, <ns3:sup>18</ns3:sup> F-FDG PET/CT showed higher specificity (95.2%, <ns3:italic>95% CI [77.3-99.8]</ns3:italic> versus 66.7%, <ns3:italic>95% CI [44.7–84.4]</ns3:italic> ) and accuracy (88.6%, <ns3:italic>95% CI [73.3-96.8]</ns3:italic> , versus 65.7%, <ns3:italic>95% CI [47.8-80.9]</ns3:italic> ) with similar sensitivity (78.6%, <ns3:italic>95% CI [49.2-95.3]</ns3:italic> versus 64.3%, <ns3:italic>95% CI [</ns3:italic> 35.1-87.2]). For distant metastases, <ns3:sup>18</ns3:sup> F-FDG PET/CT achieved markedly higher sensitivity (92.9%, <ns3:italic>95% CI [66.1–99.8]</ns3:italic> versus 50.0%, <ns3:italic>95% CI [23.0-77.0]</ns3:italic> ) and accuracy (91.4%, <ns3:italic>95% CI [76.9-98.2]</ns3:italic> versus 68.6%, <ns3:italic>CI [50.7-83.1]</ns3:italic> ), with high specificity for both (90.5%, <ns3:italic>95% CI [69.6-98.8]</ns3:italic> versus 81.0%, <ns3:italic>95% CI [58.1–94.6]</ns3:italic> ). Agreement with CECT was fair for nodes (κ=0.27) and poor for distant sites (κ=0.16). Management decisions were available in 32/35. <ns3:sup>18</ns3:sup> F-FDG PET/CT changed treatment in 15/32 (46.9%). No adverse events occurred. Conclusions In this first Tunisian series, <ns3:sup>18</ns3:sup> F-FDG PET/CT improved diagnostic performance over CECT, especially for distant metastases, and frequently redirects management. Findings support integrating its integration into melanoma care pathways when results may influence therapy. </ns3:p>