Response and outcomes of maintenance avelumab after platinum-based chemotherapy (PBC) in patients (pts) with advanced urothelial carcinoma (aUC): "Real world" experience.

472 Background: PBC followed by avelumab switch maintenance in non-progressors is the standard first line (1L) aUC treatment. We describe clinical features and outcomes in a ‘real-world’ cohort treated with avelumab maintenance for aUC. We hypothesized that outcomes would be similar with JavelinBladder100 trial data. Methods: This was a retrospective cohort study of pts from 12 sites who received 1L switch maintenance avelumab after no progression to PBC for aUC. We calculated overall response rate (ORR), median overall and progression-free survival (mOS, mPFS) using Kaplan Meier method from avelumab start. We also described OS and PFS for specific subsets using Cox regression. Results: We found 77 pts with aUC (78% pure, 22% mixed UC) with median age 68, 81% men, 91% White, 17% upper tract primary, 66% prior cisplatin, 17% liver metastasis (mets), 80% ECOG PS 0-1 at time of PBC start. There was a median of 6 weeks (range 1-30) from end of PBC to avelumab start; median follow-up time from avelumab start was 22 months (95%CI 16-24). ORR with avelumab maintenance: 28% (complete response [CR] 17%, partial response [PR] 11%), stable disease (SD) 32%; progression as best response 30% (10% unknown); mPFS 7 months (95%CI 5-9), mOS 22 months (95%CI 16-NR). Table shows HR for OS and PFS for specific subsets. Absence (vs presence) of liver mets (p=0.04), ECOG PS 0-1 (vs >1; p=0.01) and CR/PR (vs SD) to 1L PBC (p=0.03) were associated with longer OS. Conclusions:‘Real world’ outcomes with avelumab maintenance in pts with aUC align with JavelinBladder100 trial data (but higher ORR). Good PS, response to PBC and absence of liver mets are favorable prognostic factors. Limitations include moderate sample size, retrospective design, lack of randomization and central scan review, possible selection and confounding biases. Other studies (e.g. PATRIOT-II) can generate more data in pts on maintenance avelumab outside clinical trials. [Table: see text]