Avelumab maintenance therapy in patients (pts) with advanced urothelial carcinoma (UC) in Japan: Subgroup analyses by best overall response (BOR) to prior platinum-based chemotherapy (PBC) in a post-marketing surveillance (PMS) population.

4561 Background: Avelumab was approved as maintenance therapy for pts with advanced UC that has not progressed after first-line PBC based on results from the JAVELIN Bladder 100 phase 3 trial. Primary analyses of PMS data demonstrated the safety and effectiveness of avelumab maintenance in clinical practice in Japan, consistent with phase 3 results. We report post hoc analyses of PMS data in subgroups defined by BOR to prior PBC. Methods: This prospective, multicenter, observational PMS evaluated pts with advanced UC without disease progression after prior PBC who received ≥1 dose of avelumab between Feb and Dec 2021. The observation period was ≤52 wk from the start of avelumab in all pts. Safety assessment was based on occurrence of prespecified adverse drug reactions (ADRs) deemed to be associated with avelumab. Effectiveness outcomes from the start of avelumab maintenance (time to treatment failure [TTF; defined as avelumab discontinuation for any reason] and overall survival [OS]) were estimated using the Kaplan-Meier method. Subgroups were defined by BOR to prior PBC: complete response (CR), partial response (PR), or stable disease (SD). Results: The study population included 453 pts from 213 institutions. Median age was 73 y (range, 21-91); 75 pts (16.6%) were aged ≤64 y, 198 (43.7%) were aged 65-74 y, and 180 (39.7%) were aged ≥75 y. Primary tumor site was the bladder in 244 pts (53.9%) and upper tract in 209 (46.1%). Prior PBC regimen was gemcitabine + cisplatin in 267 pts (58.9%) and gemcitabine + carboplatin in 163 (36.0%). BOR to prior PBC was CR in 47 pts (10.4%), PR in 242 (53.4%), and SD in 149 (32.9%). At the end of the observation period, 128 pts (28.3%) remained on avelumab treatment and 184 (40.6%) had received next-line treatment. Median duration of avelumab treatment was 5.1 mo (IQR, 2.3-12.0). Among subgroups defined by BOR to prior PBC, the longest median TTF and highest 1-y OS rate were observed in the CR subgroup; findings were comparable in the PR and SD subgroups (Table). Safety findings were similar across subgroups. Conclusions: This PMS population represents the largest prospective observational study of avelumab maintenance therapy in pts with advanced UC in Asia. In post hoc analyses, the safety and effectiveness of avelumab were generally consistent across subgroups defined by BOR to prior PBC. Our findings support the favorable benefit-risk profile of avelumab in clinical practice, irrespective of BOR to prior PBC. BOR to prior PBC All patients (N=453) CR (n=47) PR (n=242) SD (n=149) Any-grade ADRs, n (%) 144 (31.8) 16 (34.0) 79 (32.6) 45 (30.2) Grade ≥3 ADRs, n (%) 35 (7.7) 4 (8.5) 16 (6.6) 13 (8.7) Median TTF (95% CI), mo 4.6 (3.8-5.3) 5.2 (3.4-12.0) 4.6 (3.3-5.7) 4.6 (2.8-5.6) 1-year OS rate (95% CI), % 77.9 (73.7-81.5) 89.4 (76.3-95.4) 76.3 (70.3-81.2) 75.8 (68.0-82.0)