Abstract. Purpose: The MORPHEUS platform was designed to identify early efficacy signals and evaluate the safety of novel immunotherapy combinations across cancer types. The phase Ib/II MORPHEUS-UC trial (NCT03869190) is evaluating atezolizumab plus magrolimab, niraparib, or tocilizumab in platinum-refractory locally advanced or metastatic (mUC). Additional treatment combinations were evaluated and will be reported separately. Patients and Methods: Patients had locally advanced or mUC that progressed during or following treatment with a platinum-containing regimen. The primary efficacy endpoint was investigator-assessed objective response rate (ORR). Key secondary endpoints included investigator-assessed progression-free survival (PFS) and overall survival (OS). Safety and exploratory biomarker analyses were also conducted. Results: Seventy-six patients were randomized to receive either atezolizumab plus magrolimab (n=16), atezolizumab plus niraparib (n=15), atezolizumab plus tocilizum