Inclusion Criteria:

1. The subject voluntarily participates in the study, provides written informed consent, and is able to comply with study procedures and follow-up visits.

2. Aged between 18 and 75 years.

3. Patients diagnosed with upper tract urothelial carcinoma (UTUC) who are candidates for radical nephroureterectomy with bladder cuff excision.

4. Clinical stage T1N0M0 - T2-T4aN1M0 (evaluated by CT/MRI/PET-CT).

5. Histopathology confirms urothelial carcinoma as the predominant component; IHC testing shows HER2 expression of 2+ to 3+.

6. ECOG performance status ≤ 2.

7. Laboratory parameters meet all of the following criteria:

   • Absolute neutrophil count ≥ 1.5 × 10⁹/L
   • Platelets ≥ 100 × 10⁹/L; hemoglobin ≥ 90 g/L
   • Total bilirubin ≤ 1.5 × ULN
   • Aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) ≤ 2.5 × ULN; serum creatinine ≤ 3 × ULN

8. Cardiac function: New York Heart Association (NYHA) classification < Grade III.

Exclusion Criteria:

1. Received live attenuated vaccines within 4 weeks prior to enrollment or plan to receive such vaccines during the study.

2. Received systemic chemotherapy, anti-PD-1/PD-L1 agents, or HER2-targeted therapy within the previous 6 months.

3. Known hypersensitivity to gemcitabine, Trastuzumab Rezetecan, or any of their excipients.

4. Active, known or suspected autoimmune disease.

5. Known history of primary immunodeficiency.

6. Known history of solid organ allotransplantation or allogeneic hematopoietic stem cell transplantation.

7. Female patients who are pregnant or breastfeeding.

8. Untreated acute or chronically active hepatitis B or hepatitis C infection. Patients receiving antiviral therapy may be considered eligible at the investigator's discretion with ongoing viral load monitoring.

9. Uncontrolled concurrent illnesses, including but not limited to:

   1. HIV infection (positive HIV antibody).
   2. Severe active infection with inadequate clinical control.
   3. Evidence of severe or uncontrolled systemic disease (e.g., severe psychiatric or neurological disorders, epilepsy or dementia; unstable or decompensated respiratory, cardiovascular, hepatic or renal disease; uncontrolled hypertension defined as CTCAE Grade ≥2 hypertension despite medical treatment).

10. Active bleeding, newly diagnosed thromboembolic disease requiring therapeutic anticoagulation, or bleeding diathesis.

11. Diagnosis of another malignant tumor within the past 5 years.

12. Active tuberculosis