Inclusion Criteria:

          -  Signed informed consent.

          -  Diagnosis of MCC with distant metastatic disease or recurrent, advanced locoregional
             disease not amenable to surgery or radiation

          -  Eastern Cooperative Oncology Group performance status of 0 to 1.

          -  Measurable disease according to RECIST v1.1.

          -  Availability of tumor tissue (fresh or archival) for central pathology review.

          -  Willingness to avoid pregnancy or fathering children based on protocol-defined
             criteria.

        Exclusion Criteria:

          -  Prior systemic therapy for MCC, including chemotherapy and prior PD-1 or
             PD-L1-directed therapy.

          -  Treatment with anticancer drugs or participation in another interventional clinical
             study within 21 days before the first administration of study drug.

          -  Has not recovered to ≤ Grade 1 or baseline from toxic effects of prior therapy (with
             the exceptions for anemia not requiring transfusion support and any grade of alopecia)
             and/or complications from prior surgical intervention within 7 days before starting
             study treatment.

          -  Radiation therapy administered within 2 weeks of first dose of study treatment or
             radiation therapy to the thoracic region that is > 30 Gy within 6 months of the first
             dose of study treatment.

          -  Known central nervous system (CNS) metastases and/or carcinomatous meningitis.

          -  History of second malignancy within 3 years (with exceptions).

          -  Laboratory values outside the protocol-defined range at screening.

          -  Clinically significant pulmonary, cardiac, gastrointestinal or autoimmune disorders.

          -  Active bacterial, fungal, or viral infections, including hepatitis A, B, and C.

          -  Receipt of a live vaccine within 28 days of planned start of study therapy.

          -  Current use of protocol-defined prohibited medication.

          -  Known hypersensitivity to another monoclonal antibody that cannot be controlled with
             standard measures (eg, antihistamines and corticosteroids).

          -  Inability or unlikely, in the opinion of the investigator, to comply with the Protocol
             requirements.

          -  Participant who is pregnant or breastfeeding.