A Study of Atezolizumab Versus Placebo in Combination With Paclitaxel, Carboplatin, and Bevacizumab in Participants With Newly-Diagnosed Stage III or Stage IV Ovarian, Fallopian Tube, or Primary Peritoneal Cancer

Open to females ages 18 years and up

• Participants receiving a histologic diagnosis of epithelial ovarian cancer (EOC), peritoneal primary carcinoma, or fallopian tube cancer
• Eastern Cooperative Oncology Group (ECOG) performance status of 0, 1, or 2
• Life expectancy greater than (>) 12 weeks
• For participants who receive therapeutic anticoagulation: stable anticoagulant regimen
• Availability of a representative formalin-fixed, paraffin-embedded (FFPE) tumor specimen in paraffin blocks (preferred) or at least 20 unstained slides (for detailed tissue requirements at screening)

• Received a current diagnosis of borderline epithelial ovarian tumor (formerly tumors of low malignant potential)
• Have recurrent invasive epithelial ovarian, fallopian tube, or primary peritoneal cancer that was treated only with surgery (example [e.g.], participants with Stage IA or Stage IB epithelial ovarian or fallopian tube cancers)
• Have non-epithelial ovarian tumors (e.g., germ cell tumors, sex cord stromal tumors)
• Received prior radiotherapy to any portion of the abdominal cavity or pelvis
• Received prior chemotherapy for any abdominal or pelvic tumor that include neoadjuvant chemotherapy (NACT) for ovarian, primary peritoneal or fallopian tube cancer
• Received any biological and/or targeted therapy (including but not limited to vaccines, antibodies, tyrosine kinase inhibitors) or hormonal therapy for management and/or treatment of epithelial ovarian or peritoneal primary cancer
• Have synchronous primary endometrial cancer
• Have a prior history of primary endometrial cancer, except: Stage IA cancer; superficial myometrial invasion, without lymphovascular invasion; grade less than (<) 3 or poorly differentiated subtypes, and this includes papillary serous, clear cell or other International Federation of Gynecological Oncologists (FIGO) Grade 3 lesions
• With the exception of non-melanoma skin cancer and other specific malignancies as noted above, other invasive malignancies with any evidence of other cancers present within the last 5 years or previous cancer treatment that contraindicates this protocol therapy
• Have a known hypersensitivity or allergy to biopharmaceutical agents produced in Chinese hamster ovary cells or any component of the atezolizumab and/or bevacizumab formulations
• Undergo major surgical procedure within 28 days prior to first bevacizumab dose, or anticipation of the need for a major surgical procedure during the course of the study except participants who receive NACT and will need interval surgery. This may include but is not limited to laparotomy.
• Have prior allogeneic bone marrow transplantation or solid organ transplant
• Have any other diseases, metabolic dysfunction, physical examination finding, or clinical laboratory finding giving reasonable suspicion of a disease or condition that contraindicates the use of an investigational drug or that may affect the interpretation of the results
• Have any approved or investigational anti-cancer therapy, including chemotherapy or hormonal therapy, with exceptions: Hormone-replacement therapy or oral contraceptives
• Are administered treatment with any other investigational agent or participation in another clinical study with anti-cancer therapeutic intent
• Have core biopsy or other minor surgical procedures within 7 days prior to the first dose of bevacizumab
• Have known sensitivity to any component of bevacizumab
• Have known sensitivity to any component of paclitaxel
• Current treatment with anti-viral therapy for hepatitis B virus (HBV)
• History of leptomeningeal disease