Oncological benefit of avelumab maintenance therapy for advanced or metastatic urothelial carcinoma in comparison with patients with conventional chemotherapy alone era.

711 Background: The benefit of avelumab maintenance therapy for advanced or metastatic urothelial carcinoma in real world practice remains unknown. We evaluated the oncological outcomes of avelumab maintenance therapy in comparison with conventional platinum-based 1 st line chemotherapy in real-world practice. Methods: We retrospectively evaluated 302 and 85 patients treated with and conventional platinum-based first-line chemotherapy without avelumab (chemo group) and avelumab maintenance therapy (avelumab group) between March 2004 to Sep 2024. We compared overall survival (OS) between the patients with the chemo and avelumab groups stratified by the number of cycles of first-line chemotherapy. Primary outcome was the comparison of OS in patients without progression disease (non-PD) at cycle 4 between the chemo and avelumab groups. Secondary outcomes were the impact of the administration of pembrolizumab on OS in patients with non-PD at cycle 4 in the chemo group and the comparison of OS in patients with non-PD at cycle 2-3 between the chemo and avelumab groups. Exploratory outcomes were disease-free survival (DFS) and OS based on response rate of first-line chemotherapy, first-line treatment regimen, and number of first-line chemotherapy cycles in the avelumab group. Results: We identified 124 and 49 patients with non-PD at cycle 4 in the chemo and avelumab groups, respectively. The OS from the initiation of first-line chemotherapy in the avelumab group was significantly longer than that in the chemo group (70 vs. 23 months, P = 0.009). We identified 104 and 33 patients with non-PD at cycle 2-3 in the chemo and avelumab groups, respectively. The OS from the initiation of first-line chemotherapy in the avelumab group was significantly longer than that in the chemo group (33 vs. 13 months, P = 0.002). A multivariable Cox regression analysis showed administration of avelumab was significantly associated with reduced risk of OS (hazard ratio, 0.41; P < 0.001). Of 85 patients with avelumab, the median DFS was 17 months from first-line therapy and 8.1 months from the avelumab maintenance therapy, respectively. No significant differences were observed in DFS and OS between first-line treatment regimens, and between the object response rate for first-line chemotherapy. However, the DFS and OS tended to improve in patients with first-line chemotherapy 4 cycles or more. Conclusions: We found a potential benefit of avelumab maintenance therapy on oncological outcome in real-world practice regardless of number of first-line chemotherapy. No progression within first 4 cycles of platinum-based chemotherapy might be one of the key factors for improved outcome. Further long-term follow-up is necessary.