Correlation Between Early Interval 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (PET/CT) and Circulating Tumor DNA (ctDNA) in Advanced Melanoma Patients Treated With Immune Checkpoint Inhibitors

The purpose of this research study is to determine if analysis of PET/CT scans and testing of blood samples in people with melanoma that has spread in their body can help researchers determine which patients are more or less likely to respond to immunotherapy and are more or less likely to have side effects. 24 participants will be enrolled and be on study until approximately 4 weeks after their first dose of Immune Checkpoint Inhibitor therapy.