###### Abstract  
For patients with locally advanced/metastatic urothelial carcinoma (la/mUC), first-line (IL) treatment with platinum-based chemotherapy (PBC) followed by avelumab 1L maintenance (1 LM) is a recommended therapy per treatment guidelines in patients without disease progression. However, contemporary real-world (rw) data among patients receiving this treatment are necessary to understand clinical outcomes and optimal treatment sequencing. This retrospective cohort study analyzed rw treatment patterns and clinical outcomes, including overall survival (rwOS) and progression-free survival (rwPFS), in patients with la/mUC receiving avelumab 1 LM. From the Flatiron Health database, 214 patients who received avelumab 1 LM following 1L PBC were included. From the start of avelumab 1 LM, median rwOS was 23.8 months (95% CI: 18.2--not estimable [NE]) and median rwPFS was 5.1 months (95% CI: 4.1-7.0). A total of 96 patients received second-line (2L) therapy, with 53 receiving anfortumab vedotin (EV). From the start of 2L EV, median rwOS was 11.2 months (95% CI: 6.8--NE) and median rwPFS was 4.9 months (95% CI: 3.9-8.8). Treatment patterns and clinical outcomes in this study align with guidelines and outcomes observed in the JAVELIN Bladder 100 and EV-301 clinical trials and other rw studies, supporting the use of 1L PBC followed by avelumab 1 LM and 2L EV for eligible patients.  
urothelial carcinoma; real world; treatment sequencing; clinical outcomes; survival; platinum-based chemotherapy; avelumab; enfortumab vedotin; community oncology 202 This recommendation was based on results of the pivotal JAVELIN Bladder 100 trial (JB100; NCT02603432), which found that avelumab 1 LM plus best supportive care (BSC) improved overall survival (OS) and progression-free survival (PFS) compared with BSC alone, with a median OS of 21.4 vs. 14.3 months and a median PFS of 3.7 vs. 2.0 months, in patients without disease progression following 1L PBC [5]. After \(\geq\)2 years of follow-up in all patients (data cutoff: June 4, 2021), median OS from the start of avelumab 1 LM plus BSC vs. BSC alone was 23.8 vs. 15.0 months, and median PFS was 5.5 vs. 2.1 months [6]. Cisplatin-based therapy is the preferred choice of 1L PBC, with carboplatin-based therapy used as an alternative for the 30-50% of patients not eligible for cisplatin [7, 8]. Ineligibility criteria for any platinum-based therapy include the following: (1) Eastern Cooperative Oncology Group performance status (ECOG PS) of \(\geq\)3, (2) creatinine clearance of \(<\)30 mL/min, (3) grade \(\geq\)2 peripheral neuropathy, (4) New York Heart Association heart failure class of \(>\)3, or (5) ECOG PS of 2 and creatinine clearance of \(<\)30 mL/min [9]. After 1L PBC and avelumab 1 LM or 2L immuno-oncology (IO), NCCN-preferred therapies include EV monotherapy [10] and erdafitinib [11, 12], with other recommended therapies including the antibody-drug conjugate (ADC) therapies sacituzumab govitecan [13] and trastuzumab deruxtecan [14] as well as various chemotherapy regimens [4].  
As the treatment landscape has evolved to include ADCs and targeted therapies more broadly, contemporary real-world data among patients receiving 1L PBC followed by avelumab 1 LM are needed to understand clinical outcomes and optimal treatment sequencing. This study aimed to describe baseline demographic and clinical characteristics, real-world treatment patterns, and clinical outcomes of patients with la/mUC in the US who received avelumab 1 LM following treatment with 1L PBC. Characterizing treatment sequencing patterns and outcomes following disease progression on avelumab 1 LM in a rapidly evolving therapeutic landscape was a key objective of this analysis. This study examined the clinical outcomes in patients treated with avelumab 1 LM and those treated with contemporary 2L therapies that may not have been approved at the time of JB100.