A Study of RC48-ADC Combined With Toripalimab For First-line Treatment of Urothelial Carcinoma

Inclusion Criteria: * Expected survival ≥12 weeks. * Locally advanced unresectable or metastatic UC with histopathological confirmation, including UC originating from the renal pelvis, ureters, bladder, or urethra. * Participants must not have received prior systemic therapy for locally advanced or metastatic urothelial carcinoma with the following exceptions: Participants that received neoadjuvant chemotherapy with recurrence \>6 months from completion of therapy are permitted; Participants that received adjuvant chemotherapy following cystectomy with recurrence \>6 months from completion of therapy are permitted. * At least one measurable lesion based on RECIST version 1.1 * HER2-expressing status determined by the central laboratory to be IHC 1+, 2+ or 3+. * ECOG performance status score: 0 or 1. * Adequate cardiac, bone marrow, hepatic, renal, and coagulation functions. Exclusion Criteria: * Known hypersensitivity to RC48-ADC or Toripalimab or any of its components. * History of major surgery within 4 weeks of planned start of trial treatment. * Toxicity from a previous treatment has not returned to Grade 0-1. * Prior ADCs or PD-1/PD-L1 inhibitor therapy. * Active central nervous system (CNS) metastases. * Known active hepatitis B, active hepatitis C, or human immunodeficiency virus (HIV) infection. * History of other malignancy within the previous 5 years, except for low-risk localized prostate cancer, appropriately treated carcinoma in situ of the cervix, non-melanoma skin carcinoma, or cancers with a similar curative outcome as those mentioned above. * Other serious, uncontrolled concomitant diseases that may affect protocol compliance or interpretation of outcomes, including active opportunistic infections or advanced (severe) infections, or uncontrolled diabetes. * Active autoimmune diseases that require systemic therapy over the past 2 years. Replacement therapies (such as thyroxine, insulin, or physiological replacement of glucocorticoids due to renal or pituitary deficiency) are allowed. * Assessed by the investigator to be unable or unwilling to comply with the requirements of the protocol.