Phase Ib study of anti-PD-L1 monoclonal antibody socazolimab in combination with nab-paclitaxel as first-line therapy for advanced urothelial carcinoma.

4563 Background: PD-1/PD-L1 immune checkpoint inhibitors (ICIs)0have demonstrated activity in the postplatinum and platinum-ineligible settings for advanced urothelial carcinoma (aUC). As only around 30% of patients with aUC can tolerate platinum standard treatment, first-line ICIs combined with non-platinum drugs have certain research value. Therefore we assessed the safety and efficacy of anti-PD-L1 monoclonal antibody Socazolimab in combination with nab-paclitaxel as first line therapy in aUC (NCT04603846). Methods: This is a multi-center,single-arm, phase Ib study which enrolled aUC patients with treatment-naive or first recurrence more than 6 months after the end of adjuvant chemotherapy in China. Eligible patients received Socazolimab (5mg/kg) and nab-paclitaxel (260mg/m2) every 3 weeks. Primary endpoint was to investigate the safety and tolerability of nab-paclitaxel in combination with Socazolimab. Second endpoints were the objective response rate (ORR) and progression-free survival (PFS). Results: 20 patients were enrolled, including 5 renal pelvis urothelial carcinoma, 8 bladder urothelial carcinoma, and 7 ureteral carcinoma. The median age was 69 years. As of January 14, 2022, the median follow-up time was 5.49 months. Median number of treatment cycles was 6.5 cycles. No patients had dose limiting toxicity. Among the 17 patients who had received at least one tumor assessment, 8 patients achieved partial responses. ORR was 52.94% (95% CI, 27.81-77.02). DCR was 88.24% (95% CI, 63.56-98.54). Median PFS was 8.18 months (95% CI, 5.32-13.60). Adverse reactions related to the study drug were mainly Grade 1-2. Common adverse reactions included rash (6/20,30%), increased alanine aminotransferase (6/20, 30%), increased γ-glutamyltransferase (4/20, 20%),sinus bradycardia (4/20, 20%), increased aspartate aminotransferase (4/20, 20%),pruritus (3/20, 15%). Grade 3 or higher treatment-related adverse events occurred in 4 (20%) patients, mainly Grade 3 increases in alanine aminotransferase (2/20, 10%). No confirmed treatment-related deaths occurred, and no treatment-related deaths occurred, and no new safety signals were observed. Conclusions: Socazolimab combined with nab-paclitaxel as first-line treatment was effective and well-tolerated in Chinese patients with advanced urothelial carcinoma, warranting phase II trials. Clinical trial information: NCT04603846.