Inclusion Criteria:

          -  1. Subject has provided informed consent prior to initiation of any study-specific
             activities/procedures

          -  2. Male or female age > 20 years at the time of informed consent

          -  3. Histologically confirmed diagnosis of unresectable stage III or IV melanoma as per
             AJCC staging system 8th edition

          -  4. Subject with no prior systemic treatment

          -  5. Eastern Cooperative Oncology Group (ECOG) Performance Status < 1

          -  6. Screening labs performed within 7 days of randomization demonstrating adequate
             hematologic, coagulation, liver, and kidney functions

          -  7. Indications for radiotherapy

          -  8. BRAF status must be checked, but patient is eligible regardless of BRAF mutations
             (BRAF V600 wild type or BRAF V600 mutation positive are both eligible)

        Exclusion Criteria:

          -  1. Ocular melanoma

          -  2. Active brain metastasis (stable after 1 month of radiotherapy, gamma knife surgery
             or surgery)

          -  3. Requires palliative radiotherapy

          -  4. Previous treatment with chemotherapy, a CTLA-4 or PD-1/PD-L1 antagonist agent,
             including treatment in adjuvant setting

          -  5. Autoimmune disease requiring chronic treatment with systemic corticosteroids or any
             other immunosuppressive agents 7 days prior to inclusion. (physiologic dose of
             prednisolone 10mg or equivalent are accepted)

          -  6. Concurrent medical disease which would significantly limit full compliance with the
             study such as, but not limited to the following: heart failure (III, IV as per NYHA
             classification), renal insufficiency, active infection (requires negative gest for
             clinically suspected HIV, hepatitis B virus, hepatitis C virus).

        If positive results are not indicative of true active or chronic infection, the subject may
        enter the study after discussion and agreement between the investigator and medical
        director.

          -  7. Has known malignancy that is progressing and requires active treatment

          -  8. Has known psychiatric or substance abuse disorders that would interfere with
             cooperation requirements of the trial

          -  9. Lack of availability for clinical follow-up assessments