US real-world first-line (1L) treatment patterns and outcomes for patients with metastatic urothelial carcinoma (mUC) following maintenance avelumab approval.

483 Background: The introduction of the immune checkpoint inhibitors (ICI) pembrolizumab and atezolizumab has dramatically changed the 1L mUC treatment paradigm. These agents are currently recommended by the National Comprehensive Cancer Network for platinum-ineligible patients (irrespective of programmed death-ligand 1 (PD-L1) status) and, in the case of atezolizumab, for cisplatin-ineligible patients whose tumors express PD-L1. More recently, avelumab, received approval as the first ICI for the maintenance treatment of patients who have not progressed on 1L platinum-containing chemotherapy. In this study, we described real-world 1L treatment patterns and outcomes for mUC patients following avelumab maintenance approval. Methods: We used electronic medical record data from The US Oncology Network, which includes 1,400 affiliated physicians operating in over 500 sites of care across states and treats approximately 1.2 million cancer patients annually. mUC patients diagnosed between 30 April 2020 (i.e., ~3 months before avelumab maintenance approval) and 30 June 2021 were included, with follow-up until 31 December 2021, last patient record or death, whichever occurred first. Chart review was conducted to verify mUC diagnosis, baseline characteristics, treatment patterns, and clinical outcomes. Avelumab maintenance was defined as receiving avelumab after 1L platinum-containing chemotherapy, with no documented progressive disease prior to avelumab start or as maintenance therapy indicated by physician notes. Results: A total of 249 eligible mUC patients initiated 1L treatment. Of these, 132 (53%) received ICI monotherapy, 99 (40%) received platinum-containing chemotherapy, and 18 (7%) received other treatments. Almost one-third (n=32) of those who received 1L platinum-containing chemotherapy received avelumab maintenance therapy. ICI monotherapy use increased with age, ranging from 36% among <65-year-olds to 67% among ≥75-year-olds. During a median follow-up of 14.5 months, 68 (27%) patients received second-line treatment. Median (95% confidence interval) overall survival (OS) for 1L ICI monotherapy and 1L platinum-containing chemotherapy was 10.9 (7.2, 13.0) and 16.8 (13.5, not reached) months, respectively. Conclusions: During the 18-month period following maintenance avelumab approval, in this US community oncology setting, ICI monotherapy was the most utilized 1L treatment for mUC patients, especially among older patients. The uptake of maintenance avelumab was modest. Longer follow-up is needed to further characterize OS, especially for those who received platinum therapy followed by avelumab maintenance.