Background: Patients (pts) with advanced UTC who fail first-line therapy have poor prognoses. Durvalumab (D; anti-PD-L1) 10 mg/kg every 2 weeks is approved for treatment of metastatic urothelial carcinoma (mUC) after progression on platinum-based chemotherapy (CT). Further understanding of long-term safety and efficacy of D in platinum and non-platinum pretreated pts, using a fixed dose every 4 weeks (Q4W), is of value. Methods: Module A of the phase IIIb STRONG study (NCT03084471) investigated the safety of fixed-dose D (1500 mg, Q4W) in pts with urothelial and nonurothelial UTC who progressed on or after platinum/non-platinum CT. The primary endpoint was the number of pts with adverse events of special interest (AESIs) – events with an inflammatory or immune-mediated mechanism that may require interventions (eg, steroids/immunosuppressants), including immune-mediated adverse events (imAE). AEs with onset date on or after the date of first dose and up to 90 days after study discontinuation were included. Secondary endpoints included serious AEs and overall survival (OS). Exploratory endpoints included objective response rate (ORR) and disease control rate (DCR) (investigator assessed per RECIST 1.1). Results: A total of 867 pts received D monotherapy. Median age was 68.1 yr and 80.0% were male; 87.1% had an ECOG PS 0-1 and 12.7% had ECOG PS 2. Most (96.3%) had urothelial UTC, including urothelial variants. Tumor PD-L1 expression was high (≥25%) in 239/577 (41.4%) pts with available data. Median treatment and follow-up duration were 12.1 wk (range 1-128) and 13.8 mo (range 0.0-28.8), respectively. Safety data are reported in the table. Deaths related to study treatment occurred in 9 pts (1.0%). At data cutoff (March 31, 2020), 30.8% of pts were in survival follow-up. Median OS was 7.0 mo (95% CI: 6.4-8.2); OS rate at 1 and 2 yr was 35.8% (95% CI: 32.5-39.2) and 20.2% (95% CI: 16.5-24.1), respectively. ORR was 17.7% with complete responses in 5.1% of pts. DCR at 6 mo was 33.0%. Median OS of subgroups: PD-L1 high or low: 9.3 mo (95% CI: 6.7-12.7) and 6.5 mo (95% CI: 5.8-8.1); ECOG PS 0-1 or 2: 8.4 mo (95% CI: 7.2–9.8) and 3 mo (95% CI: 2.0-4.1); urothelial and nonurothelial UTC: 7.0 mo (95% CI: 6.4-8.2) and 7.0 mo (95% CI: 2.7-10.2), respectively. Conclusions: Fixed-dose D monotherapy Q4W is convenient with an acceptable safety profile in previously treated pts for UTC. Long-term safety and efficacy data reported are consistent with published studies of D and other IO agents in this setting. Clinical trial information: NCT03084471.