Background: The standard-of-care first-line (1L) treatment for la/mUC is platinum-based chemotherapy (PBC) followed by avelumab 1L maintenance (1LM) in those who have not progressed following 1L PBC. This study aims to understand treatment patterns and real-world outcomes in patients with la/mUC in the US, including the early adoption of avelumab 1LM since its FDA approval in June 2020. Methods: Patients aged ≥18 years diagnosed with la/mUC between Jan 2015 and Jul 2021 were identified using electronic health records from the Flatiron Health database. Patient characteristics at baseline (la/mUC diagnosis) and clinical outcomes were described by 1L treatment received using the Kaplan-Meier method. Results: Of 4,387 patients included in this study, 3,706 (84.5%) received systemic treatments. Cisplatin-based therapy was the most common 1L therapy (33.3%), followed by carboplatin-based (30.9%) and immuno-oncology (IO) therapies (28.0%). Patients treated with cisplatin-based therapies had longer median progression-free survival compared with patients treated with carboplatin-based and IO therapies (8.0, 6.4, and 6.1 months, respectively). Median overall survival (mOS) in the treated cohort was 14.6 months from the initiation of 1L therapy. Patients treated with 1L cisplatin-based therapies had the longest mOS (18.3 months), followed by 1L IO therapies (14.6 months), and 1L carboplatin (13.2 months). Since July 2020, 89 patients received avelumab 1LM; the median follow-up time from the start of 1LM avelumab was 6.0 months and clinical outcomes data were immature. Of 1L-treated patients, 50.6% (n=1,874) moved onto second-line (2L) therapy during the study period. Notably, the cohort with the lowest 2L treatment rates were patients treated with 1L IO. The table demonstrates treatment sequences for this population. Conclusions: In this real-world cohort, most patients received standard-of-care platinum-based chemotherapy in 1L, with those on cisplatin-based therapy demonstrating the best outcomes. Early uptake of avelumab as 1LM was observed, and future analysis should examine the clinical outcomes of patients who received avelumab 1LM following 1L PBC.

* Treatment groups are mutually exclusive. Patients were placed into each group regardless of cross-treatment group combination with this hierarchy: IO, targeted, ADC, cisplatin, carboplatin, any other. Percentages represent row percentages