Disitamab vedotin (DV, RC48-ADC) combined with cadonilimab (anti-PD-1/CTLA-4 bispecific antibody) in patients with locally advanced or metastatic urothelial carcinoma (la/mUC): An open-label, single-arm, phase II study.

e16572 Background: The first-line regimens for locally advanced or metastatic urothelial carcinoma(la/mUC)remain an unmet need. RC48-ADC has been approved in China for platinum-refractory la/mUC with HER2 overexpression (IHC 2+ or 3+). Cadonilimab (AK104, PD-1/CTLA-4 bsAb) showed encouraging antitumor activity in gynecologic cancer, urological tumors, etc. The aim of this study is to evaluate the efficacy and safety characteristics of RC-48 ADC combined with cadonilimab in the treatment of la/mUC with HER2 expression. Methods: This is an open-label, multicenter, prospective, phase 2 trial to evaluate RC48-ADC combined with cadonilimab in mUC. The study set a safe introduction period, 6 patients were included and received the initial dose of RC48-ADC at 2 mg/kg combined with cadonilimab at 6 mg/kg every two weeks. If no DLT event occurred in the 6 patients, then continued to expand 30 patients, with an expected sample size of 36 cases; If DLT safety event occurred in 6 cases, the RC48-ADC dose reduced to 1.5 mg/kg and cadonilimab dose reduced to 4 mg/kg for Q2W; Treatment continued until disease progression, intolerable toxicity, death, etc. Primary endpoint was ORR and safety, Secondary endpoints included DOR, PFS, OS, and exploration of tumor biomarkers. Results: By the cutoff date of 4 February 2024, Thirteen la/mUC patients were enrolled who have not received systematic treatment or intolerant to cisplatin or refuse chemotherapy {8 males; median age 72 y [61-83]; 77%(10/13) of patients had distant metastasis. HER2 expression IHC 2+ or 3+ was in 85% patients (11/13), and PD-L1 low expression was 100% (6/6)}. Dose-limiting toxicity was observed (Bullous rash, ALT/AST elevated) among first 6 patients, therefore reduced cadonilimab from 6mg/kg to 4mg/kg Q2W, RC48-ADC remained. 8 patients have efficacy evaluation, ORR was 75.0% (6/8), including 12.5% CR (1/8). DCR was 100%. Median progression-free survival (PFS) and overall survival (OS) were not reached. 69.2% (9/13) Pts experienced treatment-related adverse events (TRAEs). The most common TRAEs were AST/ALT increase (30.8%), fever (23.1%), anemia (23.1%), rash (15.4%), and pruritus (15.4%), etc. TRAEs ≥G3 were occurred in 15.4%(2/13) patients, one patient died due to a cerebrovascular event. 30.8% had immune-related AEs(≥G3 irAE 15.4%), including immune-related skin reactions, hepatitis, and colitis. Conclusions: This was the first study to evaluate RC48-ADC in combination with cadonilimab (anti-PD-1/CTLA-4 bispecific antibody) in urothelial carcinoma. Preliminary results showed that the combination have promising efficacy in first-line treatment of la/mUC and a manageable safety profile, it may potentially provide a new option for la/mUC treatment, especially for those who cannot tolerate cisplatin-based chemotherapy. Clinical trial information: NCT06178601 .