Study of Tislelizumab in Combination With Chemotherapy Compared to Chemotherapy Alone for Participants With Urothelial Carcinoma

Key Inclusion Criteria: 1. Male or female aged 18 to 75 years on the day of signing the Informed Consent Form (ICF) 2. Histologically confirmed, inoperable, locally advanced, or metastatic urothelial cancer (UC) 3. Must be eligible to receive cisplatin or carboplatin in the investigator's judgment 4. Have had no prior systemic chemotherapy for locally advanced or metastatic UC 5. Must be able to provide fresh or archival tumor tissues with an associated pathological report. 6. Must have evaluable disease (either measurable or non-measurable) as defined per RECIST v1.1. 7. Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or 1. 8. Adequate organ function before randomization: Key Exclusion Criteria: 1. Received prior therapies targeting PD-1, PD-L1, PD-L2, CTLA4, or any other antibody or drug specifically targeting T-cell co-stimulation or checkpoint pathways. 2. Any approved anticancer therapy within 28 days before randomization. 3. Active leptomeningeal disease or uncontrolled, untreated brain metastasis 4. Participants with uncontrolled hypercalcemia 5. Participants with active autoimmune diseases or history of autoimmune diseases that may relapse 6. History of interstitial lung disease, noninfectious pneumonitis, or uncontrolled diseases 7. A known history of HIV infection. 8. Prior allogeneic stem cell transplantation or organ transplantation. 9. History of severe hypersensitivity reactions to other monoclonal antibodies. 10．History of allergic reactions to cisplatin, carboplatin, or other platinum-containing compounds. NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.