A Study of Atezolizumab Versus Placebo as Adjuvant Therapy in Participants With High-risk Muscle-invasive Bladder Cancer (MIBC) Who Are ctDNA Positive Following Cystectomy

Inclusion Criteria: Inclusion Criteria for the Surveillance Phase: * Histologically confirmed MIUC (also termed transitional cell carcinoma \[TCC\]) of the bladder * Tumor, nodes, and metastases (TNM) classification (based on American Joint Committee on Cancer \[AJCC\] Cancer Staging Manual, 8th Edition; Amin et al. 2016) at pathological examination of surgical resection specimen as follows: For participants treated with prior neoadjuvant chemotherapy (NAC): tumor stage of ypT2-4a or ypN+ and M0. For participants who have not received prior NAC: tumor stage of pT2-4a or pN+ and M0 * Surgical resection of MIUC of the bladder * Participants who have not received prior platinum-based NAC must be ineligible for cisplatin-based adjuvant chemotherapy, have refused it, or will not receive it based on physician's decision * ctDNA assay developed based on tumor tissue specimen and matched normal DNA from blood * Tumor programmed death ligand (PD-L1) expression per immunohistochemistry (IHC) that is evaluable by central testing of a representative tumor tissue specimen * Absence of residual disease and absence of metastasis, as confirmed by a negative baseline computed tomography (CT) or magnetic resonance imaging (MRI) scan of the pelvis, abdomen, and chest no more than 4 weeks prior to enrollment * Full recovery from cystectomy and enrollment within 24 weeks following cystectomy. Minimum of 6 weeks must have elapsed from surgery Additional Inclusion Criteria for the Treatment Phas…