Inclusion Criteria:
* Male or female patients aged ≥18 years (or legal adult age per local regulations)
* ECOG Performance Status of 0 or 1 at screening and prior to randomization.
* Histologically confirmed melanoma that is completely surgically resected with negative margins (per local standard), classified as: Stage IIB, IIC, or Stage III melanoma per AJCC Cancer Staging Manual, 8th edition.
* Patients must have undergone definitive melanoma resection ≥28 days prior to signing informed consent, and randomization must occur within 12 weeks after surgery.
* All patients must have disease-free status (ie, no evidence of locoregional recurrence or distant metastasis); no clinical evidence of brain metastases.
Exclusion Criteria:
* History of ocular/uveal and mucosal melanoma.
* Active autoimmune disease that has necessitated chronic systemic treatment within 2 years before the first study treatment
* Active, known, or suspected autoimmune disease that has required systemic treatment in past 2 years.
* Prior malignancy active within the previous 3 years, except for early-stage cancers (carcinoma in situ or Stage 1) treated with curative intent, basal cell carcinoma of the skin, squamous cell carcinoma of the skin, in situ cervical cancer, in situ prostate cancer, or in situ breast cancer that has undergone potentially curative therapy.
* Prior therapy with anti-PD-1 (including pembrolizumab), anti PD-L1, anti PD L2, anti CD137, or anti-CTLA-4 antibody (including ipilimumab or any other antibody) or agents that target interleukin-2 (IL-2) pathway any other antibody or drug specifically targeting T cell co-stimulation or checkpoint pathways.
* Requirement for systemic treatment corticosteroids (\>10 mg daily prednisone or equivalent) or other immunosuppressive medications within 14 days of randomization. Inhaled or topical steroids, and adrenal replacement steroid doses \> 10 mg daily prednisone or equivalent, are permitted in the absence of active autoimmune disease.
* History of ocular/uveal and mucosal melanoma.
* Active autoimmune disease that has necessitated chronic systemic treatment within 2 years before the first study treatment
* Active, known, or suspected autoimmune disease that has required systemic treatment in past 2 years.
* Prior malignancy active within the previous 3 years, except for early-stage cancers (carcinoma in situ or Stage 1) treated with curative intent, basal cell carcinoma of the skin, squamous cell carcinoma of the skin, in situ cervical cancer, in situ prostate cancer, or in situ breast cancer that has undergone potentially curative therapy.
* Prior therapy with anti-PD-1 (including pembrolizumab), anti PD-L1, anti PD L2, anti CD137, or anti-CTLA-4 antibody (including ipilimumab or any other antibody) or agents that target interleukin-2 (IL-2) pathway any other antibody or drug specifically targeting T cell co-stimulation or checkpoint pathways.
* Requirement for systemic treatment corticosteroids (\>10 mg daily prednisone or equivalent) or other immunosuppressive medications within 14 days of randomization. Inhaled or topical steroids, and adrenal replacement steroid doses \> 10 mg daily prednisone or equivalent, are permitted in the absence of active autoimmune disease.
* Receipt of treatment directed against the resected melanoma (eg, chemotherapy, targeted agents, biotherapy, or limb perfusion) administered after the complete resection.
* History of allergy or hypersensitivity to pembrolizumab or its excipients.
* History of severe hypersensitivity reaction (Grade ≥3) to any monoclonal antibody.
* Received prior anticancer therapy including mAb, chemotherapy, or an investigational agent or device within 5 half-lives before first dose of study intervention or not recovered (ie, \> Grade 1 or at baseline) from AEs due to previously administered agents at screening and before randomization.
* Patients with ≤ Grade 2 neuropathy are an exception and may qualify for the study.
* Received a live vaccine within 30 days prior to the first dose of study intervention.
