A Study of Atezolizumab With or Without Bevacizumab in Combination With Cisplatin Plus Gemcitabine in Patients With Untreated, Advanced Biliary Tract Cancer

Inclusion Criteria: * Considered to be eligible to receive platinum-based chemotherapy, in the investigator's judgment * Documentation of recurrent/metastatic or locally advanced unresectable disease based on computed tomography (CT) or magnetic resonance imaging (MRI) scans * Histologically or cytologically confirmed diagnosis of iCCA, eCCA, or GBC * No prior systemic therapy for advanced BTC * At least one measurable untreated lesion (per RECIST v1.1) * Adequate biliary drainage with no evidence of ongoing infection * Eastern Cooperative Oncology Group Performance Status of 0 or 1 * Life expectancy of \> 3 months * Adequate hematologic and end-organ function * For women of childbearing potential: agreement to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods, and agreement to refrain from donating eggs * For men: agreement to remain abstinent (refrain from heterosexual intercourse) or use a condom, and agreement to refrain from donating sperm Exclusion Criteria: * Recurrent disease \<=6 months after curative surgery or \<= 6 months after the completion of adjuvant therapy * Prior local regional therapy such as radioembolization * Combined or mixed hepatocellular/cholangiocarcinoma * Clinically significant hepatic encephalopathy within the 12 months prior to Day 1 of Cycle 1 * National Cancer Institute Common Terminoogy Criteria for Adverse Events Grade \>= 2 peripheral neuropathy * Prior bleeding event due to untreated or incompletely treated esophageal and/or gastric varices within 6 months prior to Day 1 of Cycle 1 * Pregnant or breastfeeding, or intending to become pregnant during the study or within 5 months after the final dose of atezolizumab or within 6 months after the final dose of bevacizumab, cisplatin or gemcitabine * Active or history of autoimmune disease or immune deficiency * History of idiopathic pulmonary fibrosis, organizing pneumonia, drug-induced pneumonitis, or idiopathic pneumonitis, or evidence of active pneumonitis on screening chest computed tomography scan * History of malignancy other than BTC within 5 years prior to screening, with the exception of malignancies with a negligible risk of metastasis or death * Symptomatic, untreated, or actively progressing CNS metastases * For patients with lung metastases, if one of the following criteria applies: Large, centrally located pulmonary metastases; Clear tumor infiltration into the thoracic great vessels seen on imaging; Clear cavitation of pulmonary lesions seen on imaging * Active tuberculosis * Co-infection with HBV and HCV * Treatment with systemic immunostimulatory agents or immunosuppressive medication * Inadequately controlled arterial hypertension * History of hypertensive crisis or hypertensive encephalopathy * Significant vascular disease * Evidence of bleeding diathesis or significant coagulopathy * Serious, non-healing or dehiscing wound, active ulcer, or untreated bone fracture * Chronic daily treatment with a non-steroidal anti-inflammatory drug (NSAID) * Preexisting renal impairment, myelosuppression, or hearing impairment