Phase II Study of Trastuzumab Rezetecan or in Combination With Adebrelimab in HER2-Expressing Locally Advanced or Metastatic Urothelial Carcinoma (la/mUC)

Inclusion Criteria: * Patients included in this study must meet all of the following criteria: 1. Age ≥ 18 years; 2. Histologically or cytologically confirmed HER2-expressing locally advanced unresectable (e.g., T4b, or N2-3) or metastatic urothelial carcinoma (la/mUC), including bladder, ureter, renal pelvis, and urethra. HER2 expression is defined as immunohistochemical (IHC) staining results of 1+ to 3+, and must be confirmed by the pathology department of Sun Yat-sen University Cancer Center according to ASCO/CAP guidelines. 3. Cohort 1: Patients who have received at least one prior systemic therapy, or relapsed/progressed within 12 months after the last treatment, or who could not tolerate treatment due to adverse events (AEs). Cohort 2: Patients who have not received prior systemic therapy or relapsed/progressed more than 12 months after neoadjuvant/adjuvant therapy, or those who could not tolerate treatment due to AEs. Cohort 3: Patients who have previously received platinum-based chemotherapy (including cisplatin, carboplatin, etc.), immunotherapy (including PD-1, PD-L1 inhibitors), and Disitamab Vedotin ; 4. At least one measurable target lesion according to RECIST 1.1 criteria; 5. ECOG performance status ≤ 2; 6. Adequate bone marrow, renal (calculated creatinine clearance \> 30 mL/min using the CG formula), hepatic, and coagulation function; 7. Expected survival ≥ 3 months; 8. The patient understands the study procedures and has provided written informed consent to participate in the study; 9. Female participants of childbearing potential must have a negative urine or serum pregnancy test within 7 days before the first administration of the study drug (Cycle 1, Day 1). If the urine pregnancy test is inconclusive, a blood pregnancy test is required. 10. Both male and female participants must agree to use highly effective contraception (i.e., methods with a failure rate of less than 1% per year) and continue contraception until at least 180 days after the end of study treatment. Exclusion Criteria: 1. Locally advanced patients who are candidates for curative local treatment; 2. Clinical history of cardiovascular, liver, respiratory, renal, hematological, endocrine, or neurological/psychiatric diseases; 3. Known or untreated spinal cord compression or active central nervous system metastases, except for those who have been treated and stable for at least 1 month and have discontinued corticosteroids for \> 2 weeks; 4. Known severe allergic reactions to the study drug's active ingredients and/or excipients, or allergy to humanized monoclonal antibody products (e.g., trastuzumab, pertuzumab); 5. Received antitumor monoclonal antibody treatment within 4 weeks before the study start, or received other antitumor therapy without recovery from adverse events; 6. Participated in any investigational drug treatment within 4 weeks before the study started; 7. Known or suspected interstitial lung disease, or moderate to severe pulmonary diseases that might interfere with the evaluation of drug-related pulmonary toxicity, including but not limited to idiopathic pulmonary fibrosis, organizing pneumonia, bronchitis obliterans, pulmonary embolism, severe asthma, COPD, restrictive pulmonary diseases, or any autoimmune, connective tissue or inflammatory lung diseases, such as rheumatoid arthritis, Sjogren's syndrome, sarcoidosis, etc., or a history of total lung resection; 8. Known hereditary or acquired bleeding disorders (e.g., hemophilia, coagulopathy); 9. Received spinal cord radiation or has not recovered from radiation-related adverse events within 4 weeks before study start; 10. Diagnosed with immunodeficiency or received systemic corticosteroid treatment or any other immunosuppressive therapy within 7 days before the first study drug administration. Physiological doses of corticosteroids (≤10 mg/day of prednisone or equivalent) are allowed; 11. Active autoimmune diseases requiring systemic treatment within the past 2 years (e.g., requiring disease-modifying drugs, corticosteroids, or immunosuppressants). Replacement therapies (e.g., thyroid hormones, insulin, or physiological corticosteroids for adrenal or pituitary insufficiency) are not considered systemic treatments. A history of non-infectious pneumonia requiring corticosteroid treatment or current interstitial lung disease within 1 year before the first dose is excluded; 12. History of organ or hematopoietic stem cell transplantation; 13. Known HIV infection (HIV 1/2 positive); 14. Untreated active hepatitis B (HBV). Note: Hepatitis B carriers with an HBV viral load \< 1000 copies/mL (200 IU/mL) before the first dose are eligible, but should receive antiviral therapy during chemotherapy to prevent reactivation. For anti-HBc (+), HBsAg (-), anti-HBs (-), and undetectable HBV viral load subjects, preventive antiviral therapy is not required, but close monitoring is necessary. 15. Active hepatitis C (HCV) infection (HCV antibody positive and HCV RNA level above detection threshold; 16. Received live vaccines within 30 days before the first dose of the study drug. Note: Inactivated flu vaccines are allowed within 30 days before the first dose, but live attenuated flu vaccines are not permitted. 17. History of other malignancies within the past 3 years, except for cured non-melanoma skin cancer, cervical carcinoma in situ, or low-risk prostate cancer (T2N0M0, Gleason score \<7, or undetectable PSA); 18. Any condition or disease history that may interfere with the study results or hinder the participant's full participation, including abnormal laboratory values, or situations deemed inappropriate by the investigator; 19. Breastfeeding women.