This clinical trial studies how well FDG-PET/CT measures early response in patients with stage III-IV melanoma who are receiving chemotherapy. Positron emission tomography (PET)/computed tomography (CT) uses a metabolic imaging radiotracer, [18F]fluorodeoxyglucose (FDG), which selectively accumulates in tumors. FDG-PET/CT of advanced melanoma before, during, and after treatment may improve methods for predicting which patients may benefit from therapy.