Inclusion Criteria:

          -  Resectable cutaneous melanoma metastatic to a lymph node and at high risk of
             recurrence

          -  Complete resection within 13 weeks before study enrollment

          -  Disease free at study entry (after surgery) with no loco-regional relapse or distant
             metastasis and no clinical evidence of brain metastases

          -  Has an FFPE tumor sample available suitable for sequencing

          -  ECOG Performance Status 0 or 1

          -  Normal organ and marrow function reported at screening

        Exclusion Criteria:

          -  Prior malignancy, unless no evidence of that disease for at least 5 years prior to
             study entry

          -  Prior systemic anti-cancer treatment (except surgery and interferon for thick primary
             melamonas. Radiotherapy after lymph node dissection is permitted)

          -  Live vaccine within 30 days prior to the first dose of pembrolizumab

          -  Transfusion of blood or administration of colony stimulating factors within 2 weeks of
             the screening blood sample

          -  Active autoimmune disease

          -  Immunodeficiency, systemic steroid therapy or any other immunosuppressive therapy
             within 7 days prior to the first dose of pembrolizumab

          -  Solid organ or allogeneic bone marrow transplant

          -  Pneumonitis or a history of (noninfectious) pneumonitis that required steroids

          -  Prior interstitial lung disease

          -  Clinically significant heart failure

          -  Known history of HIV

          -  Known active hepatitis B or C

          -  Active infection requiring treatment