Inclusion Criteria:

- Measurable metastatic Merkel cell carcinoma according to Response Evaluation Criteria
In Solid Tumors version 1.1 (RECIST v1.1), has failed at least one line of adequately
dosed chemotherapy in the metastatic setting and has subsequently progressed (where
adequate dosing is defined as a minimum of 2 cycles)

- Not eligible for participation in any ongoing clinical trial for Merkel cell carcinoma
including the Javelin Merkel 200 study (NCT02155647)

- Adequate hematological, hepatic and renal function as defined in the protocol

Exclusion Criteria:

- Brain metastases

- Prior organ transplantation, including allogeneic stem cell transplantation

- History of testing positive for human immunodeficiency virus (HIV) or known AIDS or
active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection

- Concurrent, active, malignant disease (other than Merkel cell carcinoma) with the
exception of basal or squamous cell carcinoma of the skin or carcinoma in situ as
defined in protocol

- Previous or active autoimmune disease requiring systemic immunosuppressive therapy

- Known severe hypersensitivity reactions to monoclonal antibodies, any history of
anaphylaxis, or uncontrolled asthma

- Clinically significant (that is, active) cardiovascular disease: cerebral vascular
accident / stroke (< 6 months prior to enrollment), myocardial infarction (< 6 months
prior to enrollment) unstable angina, congestive heart failure (New York Heart
Association Classification Class ≥ II), or serious cardiac arrhythmia requiring
medication

- Persisting toxicity related to prior therapy of Grade >1 NCI-CTCAE v 4.03 (alopecia
and sensory neuropathy Grade ≤ 2 is acceptable)

- Being treated with chronic systemic corticosteroids or other chronic therapeutic
immunosuppression

- Pregnant or lactating (for women of childbearing potential)

- Not using a highly effective contraception if the risk of conception exists