Study of Durvalumab Given With Chemotherapy, Durvalumab in Combination With Tremelimumab Given With Chemotherapy, or Chemotherapy in Patients With Unresectable Urothelial Cancer

Key Inclusion Criteria: * Patients with histologically or cytologically documented, unresectable, locally advanced or metastatic transitional cell carcinoma (transitional cell and mixed transitional/non-transitional cell histologies) of the urothelium (including renal pelvis, ureters, urinary bladder, and urethra) * Patients who have not been previously treated with first-line chemotherapy. Patients who have received prior definitive chemoradiation, adjuvant or neoadjuvant treatment for locally advanced disease are eligible provided that progression to locally advanced or metastatic disease has occurred \>12 months from the last therapy \[for chemoradiation and adjuvant treatment\] or \>12 months from the last surgery \[for neoadjuvant treatment\]. * At least 1 lesion, not previously irradiated, that qualifies as a RECIST 1.1 target lesion at baseline. * World Health Organization (WHO)/Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1 at enrolment * Adequate organ and marrow function as defined in the protocol * Life expectancy ≥12 weeks in the opinion of the investigator * Evidence of post-menopausal status, or negative urinary or serum pregnancy test for female pre-menopausal patients. Key Exclusion Criteria: * Prior exposure to immune-mediated therapy (with exclusion of Bacillus Calmette Guerin), including but not limited to, other anti-CTLA-4, anti-PD-1, anti-PD L1, or anti-PD-L2 antibodies, except therapeutic anticancer vaccines, which are permitted. Prior local intervesical chemotherapy or immunotherapy is allowed if completed at least 28 days prior to the initiation of study treatment. * No severe concomitant condition that requires immunosuppression medication * Untreated central nervous system (CNS) metastases and/or carcinomatous meningitis * Patients who may be eligible for or are being considered for radical resection during the course of the study. * Any medical contraindications to platinum (cisplatin or carboplatin) based doublet chemotherapy and/or known allergy or hypersensitivity to any of the study drugs or any of the study drug excipients