Inclusion Criteria:

          -  Newly diagnosed advanced (FIGO stage III-IV) epithelial ovarian, fallopian tube, or
             primary peritoneal cancer.

          -  Completed cytoreductive surgery, including at least a bilateral salpingo-oophorectomy
             and partial omentectomy, either prior to chemotherapy (primary surgery) or following
             neoadjuvant chemotherapy (interval debulking)

          -  Completed first-line platinum-based chemotherapy and surgery with a response, in the
             opinion of the Investigator

          -  Sufficient tumor tissue for planned analysis

          -  ECOG performance status of 0 or 1

          -  Patients must be 20 years of age to consent in Japan, Taiwan and South Korea; in all
             other participating countries patients must be 18 years of age to consent

        Exclusion Criteria:

          -  Pure sarcomas or borderline tumors or mucinous tumors

          -  Active second malignancy

          -  Known central nervous system brain metastases

          -  Any prior treatment for ovarian cancer, other than the first-line platinum regimen

          -  Evidence of interstitial lung disease or active pneumonitis

          -  Active, known or suspected autoimmune disease

          -  Condition requiring active systemic treatment with either corticosteroids (>10 mg
             daily prednisone equivalent) or other immunosuppressive medications