The purpose of this study is to assess whether postoperative adjuvant therapy with mRNA-4157 and pembrolizumab improves recurrence free survival (RFS) compared to pembrolizumab alone in participants with complete resection of cutaneous melanoma and a high risk of recurrence.

Key Inclusion Criteria:

• Resectable cutaneous melanoma metastatic to a lymph node and at high risk of recurrence
• Complete resection within 13 weeks prior to the first dose of pembrolizumab
• Disease free at study entry (after surgery) with no loco-regional relapse or distant metastasis and no clinical evidence of brain metastases
• Has an formalin fixed paraffin embedded (FFPE) tumor sample available suitable for sequencing
• Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or 1
• Normal organ and marrow function reported at screening

Key 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 melanomas. 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 human immunodeficiency virus (HIV)
• Known active hepatitis B or C
• Active infection requiring treatment

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