PurposeThe advent of immunotherapy by checkpoint inhibitor has profoundly changed the prognosis of patients with metastatic melanoma. The objective of our study was to evaluate the prognostic and predictive performance of 18F-FDG PET/CT of the initial extension assessment of stage IIIB-C-D and IV melanomas. MethodsWe retrospectively included 57 patients who had 18F-FDG PET/CT prior to the introduction of anti-PD-1 immunotherapy. The parameters extracted were SUVmax, SUV peak, MTV and TLG of the lesion with highest uptake (MTV LM, TLG LM), as well as MTV total and TLG total, obtained by adaptive segmentation. The18F-FDG PET/CT were dichotomized using the optimal threshold measured according to the area under the curve in the ROC (Receiver Operation Characteristic) curves. These parameters were evaluated using a Cox model. Overall survival and progression-free survival analyses were performed using the Kaplan Meier model. ResultsThe median follow-up was 25.4 months, 38 patients had progressed or recurred, and 20 patients had died. TLG LM>132.59 (P=0.0011), MTV total>12 cm3 (P=0.0139), and TLG>94.17 (P=0.0084) were significantly associated with a shorter progression-free survival. TLG LM>145.92 (P=0.0062), MTV total>10.16 cm3 (P=0.0051), and a metastatic spread>2 organs (P=0.0001) were associated with a shorter overall survival. ConclusionWe confirm the potential prognostic interest of PET-TDM at 18FDG before immunotherapy of stage IIIB-C-D and IV melanomas on progression-free survival and overall survival. The combination of these metabolic markers reflecting tumor burden with clinical and biological prognostic factors could allow early identification of patients at high risk of anti-PD-1 failure.