18 F-FDG PET/CT for the Detection of Immune-Related Adverse Events in Patients With Metastatic Melanoma Receiving Immunotherapy

Purpose: To evaluate frequency and distribution of immune-related adverse events detected by 18F-FDG PET/CT in patients with metastatic melanoma undergoing immunotherapy. Materials and Methods: Retrospective observational cohort study evaluating 147 patients with metastatic melanoma treated with immunotherapy and referred for therapy response assessment with 18F-FDG PET/CT at our institution from January 2010 to August 2022. In total, 201 PET/CT scans performed at various time points were analyzed. IRAEs detected on PET/CT were compared against clinical reference standards, including physical examinations, laboratory tests, and biopsies. Diagnostic performance metrics (sensitivity, specificity, positive predictive value, negative predictive value), and diagnostic yields were calculated. Results: There were 36/147 patients (24.5%) with IRAEs recorded according to standard of reference, with 39 IRAEs in the entire cohort. At time point level, PET/CT identified 36/36 (100%) patients with IRAEs confirmed by the reference standard, while clinical suspicion identified 26/36 (72%) cases. At IRAE level, PET/CT identified 36/39 (92%) of IRAEs confirmed by the reference standard. Thirteen out of 39 (33.3%) cases identified on PET/CT were not suspected clinically but confirmed by the reference standard. The most frequent IRAEs, both suspected clinically and on PET/CT, corresponded to thyroiditis and colitis. Among the PET/CT positive cases, the majority corresponded to grade 2 severity. Conclusion: 18F-FDG PET/CT is highly effective in detecting IRAEs in patients with metastatic melanoma on immunotherapy, uncovering clinically unsuspected events in up to 33% of cases. These results highlight its important role in early detection, guiding timely interventions, and improving overall outcomes of immunotherapy-related toxicities.