Background: Platinum-based chemotherapy (PBC) is standard first-line (1L) treatment (tx) for patients (pts) with la/mUC. On June 30, 2020, avelumab was approved in the US as 1L maintenance (1LM) for pts without disease progression following PBC. Other novel agents such as enfortumab vedotin were recently approved for second-line (2L) or later tx. Little is known about how to incorporate these agents into the optimal tx sequencing approach. This real-world (RW) study describes the characteristics and tx patterns of pts with la/mUC. Methods: A retrospective cohort of de-identified records of pts with la/mUC was obtained from the Tempus Database. Eligible pts were diagnosed with la/mUC between January 1, 2016 and February 23, 2022. Pts who completed 1L PBC were categorized as 1LM or 2L-treated. 1LM was differentiated from 2L tx based on stated clinical intent of 1LM or initiation of immunotherapy (IO) within 180 days of 1L PBC completion without disease progression. These patients were split into pre and post groups based on when they completed their 1L PBC in relation to avelumab 1LM US approval on June 30, 2020. Results: A total of 821 pts were included from community centers (21%), academic centers (27%), and ASCO CancerLinQ network sites (52%). The median age at diagnosis was 68 years (IQR, 61-75), 73% male, and 63% White. 634 (77%) pts received 1L systemic tx; of those, 62% (395/634) received PBC, 24% (155/634) received IO monotherapy, 7% (45/634) received non-PBC, and 6% (39/634) received other regimens. Tx sequencing for a subgroup of pts who discontinued 1L PBC pre- and post-avelumab 1LM approval is shown (Table). Of those receiving IO (n=84) as subsequent tx post-avelumab approval, 80% (67/84) received IO as 1LM, out of which, 84% (56/67) received avelumab as 1LM. Of the 25 pts who received 2L tx after progression on IO 1LM post-avelumab approval, enfortumab vedotin was the most commonly integrated 2L agent (n=20; 80%). Conclusions: This RW study offers valuable insight into the characteristics of pts with la/mUC treated in routine clinical practice in the US. These tx pattern data are consistent with known and evolving tx paradigms in la/mUC. In subsequent RW studies, clinical data with longer follow-up could provide further insight into the optimal tx sequencing and associated clinical outcomes.