Impact of tumor burden on treatment patterns and outcomes in patients with locally advanced or metastatic urothelial carcinoma (la/mUC) treated with avelumab first-line maintenance (1LM).

764 Background: With the evolving treatment (tx) landscape in la/mUC, patient (pt) clinical characteristics are increasingly important when selecting systemic anticancer tx. This study describes pt characteristics, tx patterns, and clinical outcomes by tumor burden in pts with la/mUC treated with avelumab 1LM following 1L platinum-based chemotherapy (PBC) with no progressive disease (PD). Methods: In this noninterventional retrospective study, pts with la/mUC were identified using Flatiron Health’s electronic health record database. Inclusion criteria were pts aged ≥18 years diagnosed with la/mUC between Jan 1, 2019, and Jul 31, 2023, treated with 1L PBC with no PD, followed by avelumab 1LM on/after Jul 1, 2020. Pt characteristics at 1LM initiation, tx patterns, and real-world overall response rate (rwORR) were reported using descriptive statistics. Real-world overall survival (rwOS), progression-free survival (rwPFS), time to next tx (TTNT), and time to tx discontinuation (TTD) were assessed using Kaplan-Meier methods. Subgroup analyses by disease burden were conducted reported: visceral (bone and other visceral) vs nonvisceral metastases (bone only) and lymph node only (includes distant lymph node) vs distant metastases. Results: Of 290 pts included, 156 (53.8%) were still receiving avelumab 1LM at data cutoff (Jul 31, 2023). Median age was 71 years; most pts were male (75.9%), White (70.7%), and had ECOG performance status 0/1 (78.3%). Median follow-up from 1LM initiation was 8.7 months. Among 266 pts with metastases, these were visceral in 142 (53.4%), nonvisceral in 124 (46.6%), distant in 183 (68.8%) and lymph node only in 83 (31.2%). 1L PBC was cisplatin-based in 52.4% and carboplatin-based in 47.6%. Median rwPFS and rwOS from avelumab 1LM initiation were 5.0 (95% CI, 3.9-5.8) and 22.0 (95% CI, 18.2-24.8) months, respectively. In pts with tumor assessment during avelumab 1LM (n=236), rwORR was 34.7%. Outcomes by disease burden are shown in the table. Conclusions: These results provide insights into clinical outcomes by tumor burden in pts with la/mUC treated with avelumab 1LM. Pts with nonvisceral and/or lymph node-only metastases had more favorable outcomes, consistent with the JAVELIN Bladder 100 trial. Outcome from 1LM start, median (95% CI), months Pts with metastases (n=266) Nonvisceral (n=124) Visceral (n=142) rwPFS 5.6 (4.1-7.8) 3.6 (3.1-5.0) rwOS 23.8 (15.4-NE) 19.1 (12.5-23.8) TTNT 6.6 (6.6-9.8) 6.0 (4.3-7.4) TTD 5.3 (4.2-10.1) 4.4 (3.5-5.7) Lymph node only (n=83) Distant (n=183) rwPFS 8.7 (5.0-NE) 3.6 (3.1-4.6) rwOS 24.3 (20.7-NE) 16.5 (12.5-22.6) TTNT 8.1 (6.2-23.8) 5.2 (4.3-6.7) TTD 10.1 (4.9-NE) 4.2 (3.3-5.5) NE, not estimable.