Neoadjuvant RC48 Plus Gemcitabine in HER2-Expressing MIBC

Inclusion Criteria: 1. Informed Consent \& Compliance: Provision of signed informed consent and ability to comply with study procedures and follow-up requirements. 2. Age: Age 18 to 75 years (inclusive). 3. Planned Surgery: Planned to undergo radical cystectomy (RC) with lymph node dissection (LND). 4. Clinical Stage: Clinical stage T2-T4aNxM0, as assessed by CT, MRI, or PET-CT. 5. Pathology \& Biomarker: Histologically confirmed predominant urothelial carcinoma by cystoscopic biopsy or transurethral resection of bladder tumor (TURBT), with HER2 expression of 1+ to 3+ determined by immunohistochemistry (IHC). 6. Performance Status: Eastern Cooperative Oncology Group (ECOG) performance status of ≤ 2. 7. Adequate Organ Function: Laboratory values meeting the following criteria: Absolute neutrophil count (ANC) ≥ 1.5 × 10\^9/L; Platelet count ≥ 100 × 10\^9/L; Hemoglobin ≥ 80 g/L; Total bilirubin ≤ 1.5 × upper limit of normal (ULN); Aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) ≤ 2.5 × ULN 8. Cardiac Function: New York Heart Association (NYHA) class \< 3. 9. Reproductive Status \& Contraception: \*Female: Must be surgically sterile, postmenopausal, or agree to use highly effective contraception during the study and for 6 months after the last dose of study treatment. Must not be lactating. \*Male: Must agree to use a medically acceptable method of contraception (e.g., condoms, abstinence) during the study and for 6 months after the last dose of study treatment. Exclusion Criteria： 1. Receipt of live attenuated vaccine within 4 weeks prior to enrollment or planned receipt during the study period. 2. Receipt of systemic chemotherapy, or anti-PD-1, anti-PD-L1, or HER2-targeted therapy within the past 6 months. 3. Known hypersensitivity to gemcitabine, disitamab vedotin, toripalimab, or any of their excipients. 4. Active, known, or suspected autoimmune disease. 5. Known history of primary immunodeficiency. 6. History of allogeneic organ transplantation or allogeneic hematopoietic stem cell transplantation. 7. Untreated acute or chronic active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. (Patients receiving continuous antiviral therapy with monitored viral loads may be eligible at the investigator's discretion). 8. Uncontrolled concurrent illness including, but not limited to: human immunodeficiency virus (HIV) infection, active or poorly controlled severe infection, or evidence of uncontrolled systemic disease (e.g., severe psychiatric/neurological disorders, decompensated respiratory failure). 9. History of other malignancies within the past 5 years, excluding clinically cured early-stage tumors. 10. Active tuberculosis.