Study closed to enrollment

Inclusion Criteria:

• Histologically and/or cytologically confirmed pleural or peritoneal malignant mesothelioma. Disease not amenable to curative surgery;
• Age 18 and over at the time of consent;
• ECOG Performance status 0-1;
• Progressed after previous receipt of 1-2 prior systemic treatment for advanced disease that included a first-line pemetrexed (or anti-folate)-based regimen in combination with platinum agent;
• Recovered from all toxicities associated with prior treatment;
• Measurable disease;
• Adequate bone marrow, hepatic, and renal function

Exclusion Criteria:

• Received any prior monoclonal antibody against CTLA-4, programmed cell death 1 (PD1) or programmed cell death 1 ligand 1 (PD-L1);
• History of chronic inflammatory or autoimmune disease;
• Active, untreated central nervous system (CNS) metastasis;
• History of other malignancy unless the subject has been disease-free for at least 3 years;
• Active or history of diverticulitis. Note that diverticulosis is permitted;
• Active or history of inflammatory bowel disease (eg, colitis, Crohn's), irritable bowel disease, celiac disease or other serious gastrointestinal chronic conditions associated with diarrhea. Active or history of systemic lupus erythematosis or Wegener's granulomatosis;
• History of sarcoidosis syndrome;
• Currently receiving systemic corticosteroids or other immunosuppressive medications;
• The last dose of prior chemotherapy or radiation therapy (with the exception of palliative radiotherapy) was received less than 2 weeks prior to randomization;
• Any unresolved toxicity NCI CTCAE Grade ≥ 2 from previous anticancer therapy; with the exception of vitiligo and alopecia.