Background: Avelumab 1LM is recommended in international guidelines for pts with la/mUC and disease control after 1L platinum-based chemotherapy (PBC). This study describes the treatment landscape after FDA approval of avelumab in June 2020 by examining pt characteristics, treatment patterns and sequencing, and rw outcomes in pts treated with avelumab 1LM. Methods: This noninterventional retrospective study identified pts with la/mUC who received avelumab 1LM in the US using data from Flatiron Health’s electronic health record database. Pts aged ≥18 y with ≥2 visits on/after Jan 1, 2011, diagnosed with la/mUC from Jan 1, 2019 - Dec 31, 2022, treated with 1L PBC followed by avelumab 1LM on/after Jul 1, 2020, ≤90 d after 1L PBC discontinuation, and with no disease progression ≤14 wk after 1L PBC were included. Treatment patterns in 1LM, second line (2L), and third line (3L) were assessed. Clinical outcomes, including rw progression-free survival (rwPFS), rw overall survival (rwOS), time to treatment discontinuation (TTD), and time to next treatment (TTNT) from 1LM or 2L initiation, were assessed using Kaplan-Meier methods. Results: 214 avelumab 1LM-treated pts met eligibility criteria. Median age was 70 y; most pts were male (77%), White (66%), and had an ECOG of 0-1 (77%). Median follow-up from 1LM was 8.7 mo. Of 96 (45%) pts who received 2L treatment post avelumab 1LM, enfortumab vedotin (EV) monotherapy (55%) was most common, followed by carboplatin-based therapy (11%). Of 40 (42%) pts who received 3L treatment, EV monotherapy was most common (25%), followed by sacituzumab govitecan (20%). Median PFS and OS from start of avelumab 1LM was 5.1 (95% CI 4.1-7.0) and 23.8 (95% CI 18.2-NE) mo. Median TTNT from avelumab 1LM initiation was 7.0 (95% CI 5.6-8.6) mo. Of pts who received 2L EV, median rwPFS and rwOS from 2L initiation were 4.9 (95% CI 3.9-8.8) and 11.2 (95% CI 6.8-NE) mo. Further rw outcomes are presented in the Table. Conclusions: Clinical outcomes in this study are aligned with those of the JAVELIN Bladder 100 trial (NCT02603432), further supporting avelumab 1LM as a standard of care. With each additional line of therapy, substantial treatment attrition and less favorable clinical outcomes were observed. This study provides insights into the sequencing of treatments and management of pts with la/mUC after disease progression with avelumab 1LM in this rapidly evolving therapeutic landscape. The use of more effective upfront therapies may decrease the attrition rates.

NE, not estimable.