Background: In the phase 3 JAVELIN Bladder 100 trial, avelumab 1L maintenance + best supportive care (BSC) significantly prolonged overall survival (OS) vs BSC alone in pts with aUC that had not progressed with 1L platinum-based chemotherapy (CTx). The JAVELIN Bladder regimen is now standard of care with level 1 evidence in international treatment guidelines. The AVENANCE study (NCT04822350), is investigating the efficacy and safety of avelumab 1L maintenance in a real-world population of pts with aUC in France. Data from the full analysis set are reported for the first time. Methods: In this ongoing, noninterventional, ambispective study, eligible pts have locally advanced or metastatic UC that has not progressed with 1L platinum-based CTx and previous, ongoing, or planned avelumab 1L maintenance treatment. The primary endpoint is OS from start of avelumab; secondary endpoints include progression-free survival (PFS), duration of treatment (DOT), and safety. Results: 591 pts received avelumab. At data cutoff (July 31, 2022), median follow-up was 12.0 mo (95% CI, 10.9-12.9). Median age was 73.1 y (IQR, 67.0-78.1). At start of 1L CTx (excluding pts with missing data), disease stage was metastatic in 524 pts (90.5%; visceral metastases in 426 [81.5%]) and locally advanced in 54 (9.3%). ECOG PS was 0-1 in 407 pts (85.3%) and 2-3 in 69 (14.5%). Tumor histology was pure UC in 528 pts (91.8%) and UC with variant or pure variant in 47 (8.2%). 1L CTx was gemcitabine + carboplatin (GemCarbo), gemcitabine + cisplatin (GemCis), dose-dense methotrexate + vinblastine + adriamycin + cisplatin (DD-MVAC), and other in 353 (61.0%), 170 (29.4%), 28 (4.8%), and 28 (4.8%) pts, respectively. Median number of cycles was 5 (range, 1-10). Median DOT with avelumab was 5.8 mo (95% CI, 5.2-7.0); 241 pts (40.8%) remained on treatment at data cutoff. The most common reasons for treatment discontinuation were disease progression (74.1% [n=258]), death (11.5% [n=40]), and adverse events ([AEs] 10.3% [n=36]). Median OS from start of avelumab was 18.4 mo (95% CI, 15.4-not estimable [NE]), the 12-month OS rate was 64.8% (95% CI, 60.0%-69.1%), and median PFS was 5.7 mo (95% CI, 5.3-7.0). In pts who had received GemCarbo, GemCis, or DD-MVAC, median OS (95% CI) was 16.2 mo (13.4-NE), not reached (NR; 18.1-NE), and NR (15.2-NE), respectively. Subgroups analyses will be presented. 218 pts received subsequent 2L, including CTx, antibody-drug conjugates, immunotherapy, and other in 186 (85.3%), 22 (10.1%), 6 (2.8%), and 4 (1.8%) pts, respectively. Any-grade treatment-related AEs (TRAEs) occurred in 217 pts (36.7%), including serious TRAEs in 29 (4.9%). Conclusions: Real-world data for avelumab 1L maintenance in pts with aUC from AVENANCE support the findings of JAVELIN Bladder 100 and confirm the clinical activity and acceptable safety profile of avelumab in a heterogeneous population. Clinical trial information: NCT04822350.