This is a prospective, single-center, single-arm phase II study evaluating whether a single postoperative intravesical instillation of disitamab vedotin (RC48) can reduce bladder recurrence after radical nephroureterectomy (RNU) in patients with HER2-positive upper tract urothelial carcinoma (UTUC). Eligible patients will receive one intravesical instillation of RC48 within 96 hours after surgery. The primary objective is to determine the 12-month intravesical recurrence rate. Serial urine samples will be prospectively collected to evaluate urinary methylation biomarkers for early recurrence detection.

Inclusion Criteria:

1. Age ≥18 years.
2. Histologically or radiologically suspected UTUC planned for RNU
3. HER2-positive tumor defined as IHC 1+, 2+, or 3+ on preoperative or surgical specimen testing.
4. ECOG performance status 0-1.
5. No prior or concomitant bladder urothelial carcinoma within 5 years.
6. Adequate hematologic, hepatic, and renal function.
7. Ability to comply with protocol-required surveillance.
8. Written informed consent. -

Exclusion Criteria:

1.Evidence of metastatic disease before enrollment. 2.Prior treatment with disitamab vedotin. 3.Prior intravesical anti-cancer therapy within 12 months. 4.Active uncontrolled infection. 5.Pregnancy or breastfeeding. 6.Severe uncontrolled cardiovascular, pulmonary, hepatic, or systemic disease. 7.Known hypersensitivity to study drug components. 8.Any condition that, in the investigator's judgment, would compromise participation or interpretation.

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