Therapeutic agents used in malignant melanoma treatment such as BRAF/MEK inhibitors and anti-CTLA-4/Anti-PD-1 antibodies go along with harmful side effects in a considerable proportion of patients and treatment costs may cause relevant medical expenditures per month. Currently, therapy response assessment in melanoma patients is performed using RECIST criteria which are based on changes in tumour size. PET/CT combines morphological and metabolic information. Thus, the so-called PERCIST-criteria were introduced integrating change in size and glucose utilization for response assessment in solid tumors. Due to the different mechanism of action these new agents introduce different response patterns increase in tumor size due to inflammation for antibody therapies). In conventional chemotherapies, re-staging is usually performed 3 months after treatment initiation which is the result of empirical investigations. Moreover, it has recently been shown, that response to new targeted therapies can be detected much earlier using PET or functional MR techniques. This forms the rationale for the monitoring of melanoma patients using a combined PET/MR technique after only 2 weeks of therapy initiation. Especially for patients in stage IV with a medium survival time of 12 months, a 2.5 months earlier re-staging and therapy adjustment would have significant consequences for the individual clinical course.

Inclusion Criteria:

• patient with diagnosed unresectable malignant melanoma stage IV
• age: ≥18 years
• planned systemic therapy with either new therapies (BRAF/MEK inhibitors, Anti-CTLA-4/Anti-PD-1 antibodies) or conventional chemotherapeutics (CTx)
• clinically indicated routine PET/CT (baseline t0) demonstrating at least one measurable lesion
• PET/CT for baseline-staging and therapy monitoring (clinical indication required)
• informed consent

Exclusion Criteria:

• contraindications for MR-imaging (metal implants, claustrophobia, etc.)
• contraindications for gadolinium-based contrast agent
• acute infections or other acute diseases
• pregnant or breast-feeding women
• disability for informed consent