[68Ga]Ga-FAPI Total Body PET/CT for Better and Faster Imaging in Cancer

The goal of this clinical trial is to investigate the use of the tracer \[68Ga\]Ga-FAPI-46 for PET/CT-imaging in response evaluation of patients with advanced stage malignant melanoma treated with immune checkpoint inhibitor therapy (ICT). The main question it aims to answer is: • Can \[68Ga\]Ga-FAPI-46 PET/CT improve response evaluation in patients suffering from advanced stage malignant melanoma treated with ICT and potentially serve as a biomarker. Researchers will compare findings on the experimental \[68Ga\]Ga-FAPI-46 PET/CT with findings on standard imaging (\[18F\]FDG PET/CT). Participants will undergo: * Two \[68Ga\]Ga-FAPI-46 PET/CT scans: one before treatment initiation with ICT and one after three months. * Two blood samples * Passive follow-up 6 months after the last scan \[68Ga\]Ga-FAPI-46 PET/CT