674 Background: Avelumab first-line maintenance (1LM) was approved in Japan in February 2021 based on the results of the phase III JAVELIN Bladder 100 trial, which showed an overall survival (OS) benefit in patients with locally advanced or metastatic urothelial carcinoma (la/mUC) after 1L platinum-based chemotherapy (PBC). We report long-term real-world effectiveness and treatment patterns from JAVEMACS, a multicenter retrospective chart review. Methods: Patients with la/mUC who received 1L PBC and initiated avelumab 1LM between February 2021 and December 2023 were identified across multiple centers. Data were extracted from medical charts and integrated into a centralized electronic data capture system. Patient characteristics, effectiveness (OS, progression free survival PFS, PFS from 1LM start to second-line 2L progression or death PFS2), and treatment patterns were analyzed. Multivariable Cox models were used to identify prognostic factors for OS. Results: The study included 349 patients. At data cutoff (31 May 2025), median observation period was 34.0 months (95% CI, 30.5–36.7). At 1LM start, median age was 73 years (range, 43–93); 74.2% were male; ECOG PS was 0 in 81.4% and ≥1 in 17.5% patients. Primary tumor site was bladder in 50.7% and renal pelvis/ureter in 47.9% patients, and 39.8% had a history of radical surgery. 1L PBC regimen was gemcitabine/cisplatin in 56.2% and gemcitabine/carboplatin in 33.0% patients. Median 1L PBC cycles was 4 (IQR, 4–4). Median duration from 1L PBC start to 1LM start was 19.2 weeks (IQR, 15.4–24.2). At the last follow-up, median 1LM duration was 4.9 months (IQR, 2.1–12.6; 12 months: 25.5%); 49 (14.0%) patients were still on 1LM. Of 300 patients who discontinued 1LM, 221 (73.7%) received 2L therapy, with enfortumab vedotin 148 (67.0%) being the most used. Forty-seven (13.5%) patients received curative-intent local therapy (radiation or surgery) to the primary or metastatic sites after 1LM start. Survival results were summarized in the Table. After multivariable adjustment, ECOG PS, liver metastasis at 1L PBC start, serum C-reactive protein, and best overall response to 1L PBC were independent prognostic factors for OS after starting 1LM (all p < 0.05). Conclusions: In this Japanese real-world cohort of la/mUC patients who did not progress after 1L PBC, avelumab 1LM demonstrated favorable long-term outcomes. These findings support routine use and the value of prognostic assessment at 1LM initiation. Median (95% CI), months OS from 1LM PFS from 1LM PFS2* from 1LM Overall (N=349) 30.6 (24.6–40.1) 7.3 (6.0–8.7) 20.2 (16.0–24.6) *From 1LM start until 2L progression or death, whichever occurs first. 1LM, first-line maintenance; 2L, second-line; OS, overall survival; PFS, progression free survival.
Kobayashi et al. (2026) studied this question.