Inclusion Criteria:

          -  Male or female patients, age 12 years or older at the time of signing the informed
             consent form (age 18 years or older where local regulations, countries, and/or
             institutional policies do not allow for patients < 18 years of age (adolescents) to
             participate). In regions where adolescents are not allowed to participate in the study
             due to age restrictions, enrolled patients must be ≥ 18 years of age.

          -  Histologically confirmed Stage IIIA (LN metastasis > 1 mm), IIIB/C/D, or IV
             (M1a/b/c/d) cutaneous melanoma by AJCC (8th edition) at study entry that has been
             completely surgically resected within 12 weeks prior to randomization.

          -  Tumor tissue available from biopsy or resected disease must be provided to central
             laboratory for PD-L1 status analysis. Must have PD-L1 expression classification for
             stratification purposes.

          -  Disease-free status documented by a complete physical examination and imaging studies
             within 28 days prior to randomization.

        Exclusion Criteria:

          -  History of ocular/uveal melanoma or mucosal melanoma.

          -  Active, known or suspected autoimmune disease. Patients with Type I diabetes mellitus,
             hypothyroidism only requiring hormone replacement, skin disorders not requiring
             systemic treatment, or conditions not expected to recur in the absence of an external
             trigger are permitted to enroll.

          -  Conditions requiring systemic treatment with either corticosteroids (> 10 mg daily
             prednisone equivalent) or other immunosuppressive medications within 14 days of
             randomization. Inhaled or topical steroids, and adrenal replacement steroid doses > 10
             mg daily prednisone equivalent, are permitted in the absence of active autoimmune
             disease.

          -  Prior therapy for melanoma except surgery for the melanoma lesion(s) and/or adjuvant
             radiation therapy for central nervous system lesions.

          -  Prior therapy with interferon, talimogene laherparepvec (Imylgic®), interleukin-2
             (IL-2) directed therapy, anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or
             anti-cytotoxic T lymphocyte-associated protein 4 antibody (including ipilimumab or any
             other antibody or drug specifically targeting T cell co-stimulation or checkpoint
             pathways).

          -  Prior malignancy active within the previous 3 years except for locally potentially
             curable cancers that have been apparently cured.