Preliminary efficacy and safety results from RC48-C017: A phase II study of neoadjuvant treatment with disitamab vedotin plus toripalimab in patients with muscle invasive bladder cancer (MIBC) with HER2 expression.

4568 Background: Disitamab vedotin (DV) is a novel humanized anti-HER2 antibody-drug conjugate. DV plus toripalimab (a recombinant humanized anti-PD-1 monoclonal antibody) showed promising antitumor activity in metastatic urothelial carcinoma (ASCO 2023). This study aimed to evaluate the safety and efficacy of DV plus toripalimab as neoadjuvant therapy in MIBC patients with HER2 expression. Methods: This is a prospective multicenter phase 2 trial which planned to enroll 40 pts. Primary endpoint is pathological CR (pCR) rate; secondary endpoints include pathologic response rate, safety and tolerability. Study enrolled pts who are previously untreated MIBC (cT2-T4aN0-1M0), medically fit for and agree to undergo curative intent RC+PLND. HER2 expression was required to be immunochemistry (IHC) ≥ 1+ tested locally. Pts received DV 2 mg/kg plus toripalimab 3 mg/kg every two weeks for 6 cycles, followed by RC+ PLND within 4 weeks. Here we present preliminary efficacy and safety results. Results: 44 pts were enrolled and clinical stage at diagnosis was: cT2N0 (38.6%), cT3N0 (29.5%), cT4aN0 (13.6%), cT2-4aN1 (18.2%). HER2 expression of IHC 1+, 2+ or 3+ was 11.4%, 56.8%, and 31.8%, respectively. By the data cut-off date (Feb-2024), 29 pts (65.9%) completed RC + PLND. The pCR rate was 62.1% (18/29). The pathologic response rate was 75.9% (22/29). Common treatment-related adverse events (TRAEs) were mostly Grade 1 or 2, including alopecia (36.4%), alanine aminotransferase increased (31.8%), aspartate aminotransferase increased (25.0%), rash (22.7%), gamma-glutamyl transferase increased (22.7%), peripheral sensory neuropathy (22.7%), and asthenia (20.5%). Grade 3-4 TRAEs were reported in 15.9% of pts. No deaths occurred. No surgery was cancelled due to TRAEs. Survival data are not yet mature. Conclusions: Neoadjuvant treatment with DV plus toripalimab showed promising efficacy results and was well tolerated in operable MIBC pts with HER2 expression. These results will support further investigation for DV plus toripalimab in this population. Clinical trial information: NCT05297552 .