Metabolic Imaging in Electrochemotherapy: Insights from FDG-PET Analysis in Metastatic Melanoma-A Pilot Study

Background/Objectives: Electrochemotherapy (ECT) has emerged as a promising locoregional treatment modality for patients with cutaneous and subcutaneous melanoma metastases. While systemic therapies have improved overall disease control, effective local tumor management remains crucial, particularly in oligometastatic or symptomatic disease. This pilot study investigates the role of metabolic imaging with [¹⁸F]FDG PET/CT to assess tumor metabolism in melanoma patients undergoing ECT, building on prior evidence that PET offers valuable functional information beyond anatomical changes detected by conventional imaging. Methods: This retrospective study included 11 patients with histologically confirmed melanoma and cutaneous or subcutaneous metastases treated with ECT. [¹⁸F]FDG PET/CT scans were performed either before ECT, after ECT, or both. Metabolic response was assessed by measuring the tracer uptake (SUV_max) of the ten hottest lesions. Morphological changes were evaluated using CT. Local progression-free survival was determined. Results: A total of 66 lesions were analyzed. Patients with PET/CT only after ECT showed significantly higher SUV_max and lesion size compared to those imaged before treatment (mean SUV_max: 9.9 ± 11.2 vs. 10.3 ± 5.5; p = 0.034). Progression-free survival differed significantly based on pre-ECT SUV_max values (χ² = 3.90; p = 0.048). Among two patients with follow-up imaging, one showed new lesions on CT with only mild FDG uptake, while the other developed newly FDG-avid metastases after ECT. Conclusions: FDG PET/CT provides valuable information on tumor viability and treatment response in melanoma patients undergoing ECT, demonstrated by significant differences in metabolic activity between lesions imaged before and after treatment. The lack of longitudinal intra-individual imaging limits definitive conclusions about the direct metabolic effects of ECT.