['melanoma']
['placebo']

        Inclusion criteria:

          -  Completely resected Stage III melanoma

          -  Tumor tissue available for evaluation of PD-L1 expression

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1

          -  Adequate organ function

          -  No prior therapy for melanoma except surgery for primary melanoma lesions (or
             previously treated with interferon for thick primary melanomas without evidence of
             lymph node involvement are eligible)

          -  Female participants of childbearing potential should be willing to use adequate
             methods of birth control or be surgically sterile, or abstain from heterosexual
             activity for the course of the study through 120 days after the last dose of study
             medication

          -  Male participants should agree to use an adequate method of birth control starting
             with the first dose of study therapy through 120 days after the last dose of study
             medication

        Exclusion criteria:

          -  Mucosal or ocular melanoma

          -  History of (non-infectious) pneumonitis that required steroids or current pneumonitis

          -  History of or current interstitial lung disease

          -  History of hematologic or primary solid tumor malignancy, unless no evidence of that
             disease for 5 years

          -  Active autoimmune disease that has required systemic treatment in past 2 years

          -  Active infection requiring therapy

          -  Unstable hyperthyroidism or hypothyroidism

          -  Diagnosis of immunodeficiency

          -  Systemic steroid therapy or any other form of immunosuppressive therapy within 7 days
             prior to the first dose of study medication

          -  Known history of human immunodeficiency virus (HIV), active Hepatitis B or C

          -  Treatment with live vaccine within 30 days prior to the first dose of study medication
             are not eligible

          -  Prior treatment with any anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA4)
             monoclonal antibody or anti-programmed cell death receptor 1 (PD-1), anti-programmed
             cell death receptor ligand 1 (PD-L1), or anti-programmed cell death receptor ligand 2
             (PD-L2) agent, or prior participation in any Merck pembrolizumab clinical trial

          -  Currently participating and receiving study therapy, or participated in a study of an
             investigational agent and received study therapy or used an investigation device
             within 4 weeks of the first dose of study medication

          -  Pregnant or breastfeeding, or expecting to conceive or father children within the
             projected duration of the trial, starting with the screening visit through 120 days
             after the last dose of study medication

          -  Participant is or has an immediate family member (e.g., spouse, parent/legal guardian,
             sibling or child) who is investigational site or Sponsor staff directly involved with
             this trial without prospective Institutional Review Board approval (by chair or
             designee) is given
      