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