An Efficacy Study of Adjuvant Treatment With the Personalized Cancer Vaccine mRNA-4157 and Pembrolizumab in Participants With High-Risk Melanoma (KEYNOTE-942)

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