This study evaluates the effectiveness of first-line immunotherapy in patients with metastatic melanoma treated at the Institute of Oncology Ljubljana in Slovenia. The main objectives are to assess treatment response rates, progression-free survival, and treatment safety, and to identify prognostic and predictive biomarkers associated with response to immunotherapy.

Biological samples including blood, stool, and body fluids (if available) will be collected at predefined time points and analyzed for molecular tumor markers. Imaging assessments (CT or PET/CT) will be performed before treatment initiation and during follow-up to evaluate response.

The study aims to improve identification of patient subgroups who benefit from immunotherapy and those who do not, supporting better personalized treatment strategies.

Metastatic melanoma is a malignant skin cancer with significant morbidity and mortality. In recent years, immunotherapy has become a standard first-line treatment option for metastatic melanoma, but clinical benefit varies substantially among patients. Reliable prognostic and predictive biomarkers are needed to identify patients who are likely to respond to immunotherapy and those who may require alternative strategies.

This prospective study is conducted at the Institute of Oncology Ljubljana and evaluates the effectiveness of first-line immunotherapy in patients with metastatic melanoma treated in Slovenia. The primary clinical outcomes include overall response rate, progression-free survival, and safety of treatment.

Patients will undergo routine imaging examinations (CT or PET/CT of the head, chest, and abdomen) prior to the start of immunotherapy and at follow-up time points (week 4, week 12, and week 28), and additionally as clinically indicated. Imaging results will be used to evaluate disease response to treatment.

In parallel, biological samples will be collected at the same time points, including peripheral blood (10 mL), stool samples, and samples of pleural or peritoneal effusions when present. Samples will be analyzed for molecular tumor markers to explore associations with clinical response and survival outcomes.

The study aims to identify biomarker-based subgroups of patients for whom immunotherapy is beneficial and those for whom it is not, contributing to improved individualized treatment approaches in metastatic melanoma.

Inclusion Criteria:

• Age ≥ 18 years
• Metastatic (diffuse) melanoma
• Planned first-line immunotherapy treatment
• Signed informed consent for participation in the study

Exclusion Criteria:

• Age < 18 years
• Inability to provide informed consent
• Any condition preventing participation or sample collection according to investigator judgment