Melanoma is an aggressive malignancy with a high mortality rate. Accurate diagnosis and prognostic risk assessment are essential to the clinical management of melanoma. Melanin is present in most melanoma and has become a potential target for melanoma. This team has successfully synthesized a positron nuclide targeting melanin probe named 18F-PFPN (18F-N-(2-diethylaminoethyl)-4-(2-\[2-ethoxy\]-ethoxy) pyridine), which has been proven to be safe and well-tolerated. It has shown excellent diagnostic value in both primary and metastatic melanoma. This prospective study was designed to further investigate the prognostic value of 18F-PFPN for melanoma and compare it with the general metabolic imaging agent 18F-FDG. In this study, patients with clinically highly suspected or confirmed melanoma who underwent 18F-PFPN and 18F-FDG PET scans will be enrolled consecutively. Patients' PET images, clinical characteristics, and follow-up information will be collected for prognostic analyses.