Background: In the phase 3 JAVELIN Bladder 100 trial (NCT02603432), avelumab 1L maintenance + best supportive care (BSC) significantly prolonged overall survival (OS) vs BSC alone in patients (pts) with aUC that had not progressed with 1L platinum-based chemotherapy. We report exploratory analyses in subgroups defined by response to 1L chemotherapy (complete response [CR], partial response [PR], or stable disease [SD]) after ≥2 years of follow-up. Methods: Eligible pts had unresectable locally advanced or metastatic UC without progression with 4-6 cycles of 1L gemcitabine + cisplatin or carboplatin. Pts were randomized 1:1 to receive avelumab + BSC (n = 350) or BSC alone (n = 350), stratified by best response to 1L chemotherapy (CR/PR vs SD) and visceral vs nonvisceral disease at start of 1L chemotherapy. Results: At data cutoff (June 4, 2021), median follow-up in both arms was ≥38 months. OS and PFS were longer in the avelumab + BSC vs BSC alone arm in all subgroups (Table). Median duration of study treatment and incidence of grade ≥3 treatment-emergent adverse events (TEAEs) in subgroups are shown in the Table. In the avelumab + BSC vs BSC alone arm, respectively, subsequent second-line anticancer drug therapy was received by: CR subgroup, 50.0% vs 74.2%; PR subgroup, 58.3% vs 71.8%; and SD subgroup, 46.4% vs 70.4%. Conclusions: Long-term follow-up from JAVELIN Bladder 100 continues to show prolonged OS and PFS with avelumab + BSC vs BSC alone irrespective of response (CR, PR, or SD) to 1L chemotherapy and despite a higher proportion of pts in the BSC alone arm receiving subsequent therapy. Long-term safety was consistent across subgroups. These findings further support avelumab 1L maintenance as standard of care for all pts with aUC that has not progressed with 1L platinum-based chemotherapy. Clinical trial information: NCT02603432.

*In treated pts