1. Screen and recruitment: patients will be screened based on their prior history and intention to initiate treatment with an immune checkpoint inhibitor.

2. Study phase:

   • Collection of baseline demographic data, prior disease history, nature of ICI therapy, outcome data of ICI therapy (treatment disposition, toxicity, tumor response and survival).
   • Collection of blood samples will be performed every 3 to 4 weeks for the first year on ICI therapy and every 6 to 12 weeks thereafter until the end of ICI therapy, disease progression, death or loss to follow-up. Collection of blood samples will be aligned with the visits necessary for the administration of the ICI therapy.
   • Collection of archival melanoma metastasis tissues will be performed on a continuous basis and be triggered by availability of such tissue following therapeutic resections of melanoma metastases.

3. Follow-up phase

1. Screen and recruitment: patients will be screened based on their prior history and intention to initiate treatment with an immune checkpoint inhibitor. This screening of candidate patients by the investigators will be non-interventional. Patients that are considered eligible candidates will be invited to participate in this study and to Page 3/18 provide written informed consent.

2. Study phase:

   • Collection of baseline demographic data, prior disease history, nature of ICI therapy, outcome data of ICI therapy (treatment disposition, toxicity, tumor response and survival).
   • Collection of blood samples will be performed every 3 to 4 weeks for the first year on ICI therapy and every 6 to 12 weeks thereafter until the end of ICI therapy, disease progression, death or loss to follow-up. Collection of blood samples will be aligned with the visits necessary for the administration of the ICI therapy.
   • Collection of archival melanoma metastasis tissues will be performed on a continuous basis and be triggered by availability of such tissue following therapeutic resections of melanoma metastases.

3. Follow-up phase: patients who stop treatment with the immune checkpoint inhibitor will be followed-up for

Inclusion Criteria:

1. Histologically confirmed malignant melanoma;
2. AJCC Stage IIIC or IV melanoma with evaluable disease;
3. Treatment with an immune checkpoint inhibitor;
4. Willing and able to give written informed consent;
5. Accessible for treatment and follow-up;

Exclusion Criteria:

• non

All patient with an unresectable stage III or stage IV melanoma treated with pembrolizumab