Trastuzumab in Combination With Serplulimab and Chemotherapy for the Treatment of HER2-overexpressing Unresectable Locally Advanced or Metastatic Biliary Tract Cancer or Urothelial Carcinoma After Failure of Standard Therapy

Inclusion Criteria: * Age 18 to 75 years, male or female. * Histologically or cytologically confirmed recurrent and/or metastatic advanced biliary tract cancer or urothelial carcinoma. * Disease progression after at least one prior line of systemic antitumor therapy. For patients who received systemic antitumor therapy during adjuvant therapy or concurrent chemoradiotherapy, progression occurring within 6 months after completion of therapy is considered as one prior line of therapy. * HER2 overexpression confirmed by immunohistochemistry (IHC) 3+ or IHC 2+ with in situ hybridization (ISH)+. * Left ventricular ejection fraction (LVEF) ≥ 50%. * No prior anti-HER2 therapy. * At least one measurable lesion according to RECIST version 1.1. * Eastern Cooperative Oncology Group (ECOG) performance status score of 0 or 1. * Adequate organ reserve function: * Urine protein ≤ 1+ on urinalysis or 24-hour urine protein \< 1.0 g, and albumin \> 2.7 g/dL. * Life expectancy ≥ 3 months as judged by the investigator. * Ability to provide written informed consent and understand and agree to comply with study requirements and assessment schedule. * Female patients of childbearing potential must agree to use highly effective contraception during the treatment period and for 12 weeks after the last dose; male patients must agree to use highly effective contraception during the treatment period and for 6 months after the last dose. Exclusion Criteria: * Known HER2-negative or HER2-low expression…