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

Résumé

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 ( 18 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 18 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 18 F-FDG PET/CT. Results Of 51 screened, 35 patients were included (23 staging and 12 restaging). Compared with CECT, 18 F-FDG PET/CT reclassified stage in 22/35 (62.9%), upstaging 14 (40.0%) and downstaging 8 (22.9%). For nodal disease, 18 F-FDG PET/CT showed higher specificity (95.2%, 95% CI [77.3-99.8] versus 66.7%, 95% CI [44.7–84.4] ) and accuracy (88.6%, 95% CI [73.3-96.8] , versus 65.7%, 95% CI [47.8-80.9] ) with similar sensitivity (78.6%, 95% CI [49.2-95.3] versus 64.3%, 95% CI [ 35.1-87.2]). For distant metastases, 18 F-FDG PET/CT achieved markedly higher sensitivity (92.9%, 95% CI [66.1–99.8] versus 50.0%, 95% CI [23.0-77.0] ) and accuracy (91.4%, 95% CI [76.9-98.2] versus 68.6%, CI [50.7-83.1] ), with high specificity for both (90.5%, 95% CI [69.6-98.8] versus 81.0%, 95% CI [58.1–94.6] ). 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. 18 F-FDG PET/CT changed treatment in 15/32 (46.9%). No adverse events occurred. Conclusions In this first Tunisian series, 18 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.

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