A Study to Evaluate The Efficacy And Safety Of RO7198457 In Combination With Pembrolizumab Versus Pembrolizumab Alone In Participants With Previously Untreated Advanced Melanoma.

Open to people ages 18 years and up

• Histologically confirmed metastatic (recurrent or de novo Stage IV) or unresectable locally advanced (Stage IIIC or IIID) cutaneous, acral, or mucosal melanoma;
• Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1;
• Life expectancy >/= 12 weeks;
• Adequate hematologic and end-organ function;
• Naive to prior systemic anti-cancer therapy for advanced melanoma with some exceptions;
• Tumor specimen availability;
• Measurable disease per RECIST v1.1.

• Ocular/uveal melanoma;
• Any anti-cancer therapy with the exceptions as specified in the protocol;
• Symptomatic, untreated, or actively progressing central nervous system (CNS) metastases;
• Previous splenectomy;
• History of autoimmune disease;
• Prior allogeneic bone marrow transplantation or prior solid organ transplantation;
• Positive test for Human Immunodeficiency Virus (HIV) infection;
• Active hepatitis B or C or tuberculosis;
• Significant cardiovascular disease;
• Known clinically significant liver disease.