To evaluate the efficacy and safety of RC48-ADC, a novel humanized anti-HER2 antibody conjugated with monomethyl auristatin E, in patients with HER2 locally advanced or metastatic urothelial carcinoma (mUC) refractory to standard therapies.

This was a phase II, open-label, multicenter, single-arm study of patients with HER2 (IHC status 3+ or 2+) locally advanced or mUC who previously failed at least one line of systemic chemotherapy. The primary endpoint was the objective response rate (ORR) assessed by a blinded independent review committee (BIRC). The secondary endpoint included progression-free survival (PFS), disease control rate, duration of response, overall survival (OS), and safety.

Forty-three patients were enrolled. The median follow-up was 20.3 months. The overall confirmed ORR as assessed by the BIRC was 51.2% [95% confidence interval (CI), 35.5%-66.7%]. Similar responses were observed in prespecified subgroups, such as those with liver metastasis and those previously treated with anti-programmed cell death 1 (PD-1)/programmed death ligand 1 (PD-L1) therapies. The median PFS and OS were 6.9 months (95% CI, 5.6-8.9) and 13.9 months (95% CI, 9.1-NE), respectively. The most common treatment-related adverse events (TRAE) were hypoesthesia (60.5%), alopecia (55.8%), and leukopenia (55.8%). Twenty-five (58%) patients experienced grade 3 TRAEs, including hypoesthesia (23.3%) and neutropenia (14.0%). No grade 4 or grade 5 TRAEs occurred.

RC48-ADC demonstrated a promising efficacy with a manageable safety profile in patients with HER2 locally advanced or mUC who had failed at least one line of systemic chemotherapy.