Preliminary results from a multi-center phase Ib/II study of RC48-ADC combined with tislelizumab as neoadjuvant treatment in patients with HER2 positive locally advanced muscle-invasive urothelial bladder cancer (Hope-03).

e16595 Background: To evaluate the safety and efficacy of RC48-ADC, a humanized anti-HER2 antibody conjugated with monomethyl auristatin E, and tislelizumab, a PD-1 antibody, as a novel neoadjuvant treatment combination in patients with HER2 positive locally advanced muscle-invasive bladder cancer (MIBC). The study design has been presented at 2022 ESMO Asia meeting. The preliminary results would be reported this time. Methods: This is a Ib/II, multi-center, open-label, single-arm study (ChiECRCT20210564). 51 patients with pathological and imaging diagnosed cT2-4bN0-3M0-1a HER2 positive MIBC will be included. RC48-ADC is given every 2 weeks with a maximum dose of 120mg intravenously, and tislelizumab is given every three weeks at the dose of 200mg intravenously. Treatment efficacy will be performed by imaging and transurethral resection of tumors after the neoadjuvant treatment. Patients without disease progression will receive radical cystectomy or bladder-sparing therapies based on individual risk profiles and preferences. The primary endpoints are clinical complete remission rate (cCR, T0/Ta/Tis), pathological complete remission rate (pCR) and safety. The secondary endpoints are disease control rate (DCR), overall survival (OS), local recurrence free survival (LRFS), distant metastasis free survival (DMFS) and quality of life. Results: Until now, 18 patients were included successfully, with 3 female patients and 15 male patients. And the median age was 64.47 years old. Of them, 7 patients were HER2(2+), and 11 patients were HER2(3+). The clinical stages were T2-4aN0-3M1a. Sixteen patients had the primary efficacy evaluation by now. After the neoadjuvant treatment, 7 patients were T0, 4 patients Tis, 2 patients partial response (PR), 2 patients stable disease (SD) and 1 patient suffered from progress of local disease. Hence the cCR rate was 68.75%, and the DCR was 90.91%. Fourteen patients chose radiotherapy as bladder-sparing therapy and no evidence of tumor in 6 patients who received treatment efficacy after radiotherapy. Two patients received radical cystectomy and pT3N0M0 was achieved for both. No patient died so far. For safety analysis, 4 patients suffered from immune-related adverse event, namely, grade 2 myositis, grade 1 elevated transaminase and grade 1 hyperthyroidism which led to treatment interruption of tislelizumab. And 10 patients experienced RC48-ADC related toxicities, including grade 1 elevated transaminase, grade 1 erythra and grade 1 paresthesia. No treatment related dose reduction happened. Conclusions: The novel neoadjuvant combination of RC48-ADC and tislelizumab showed promising down stage efficacy in patients with HER2 positive locally advanced MIBC and the toxicities were manageable, which would be verified by the final analysis. Clinical trial information: ChiECRCT20210564.