Inclusion Criteria:
* 1\. Willing to sign the ICF and follow the requirements specified in the protocol.
2\. Aged 18 to 75 (including 18 and 75), both genders. 3. Expected survival time ≥ 12 weeks. 4. Patients with unresectable locally advanced or metastatic urothelium cancer confirmed by histopathology.
5\. Patients who have failed prior platinum-based chemotherapy and PD-1/PD-L1 inhibitors and have have progressive disease or recurrence on or after their most recent therapy.
6\. Archival or biopsy tumor specimens should be provided (primary or metastatic).
7\. HER2 positive (IHC 3+ or IHC 2+) in the tumor specimens confirmed by central laboratory test.
8\. Patients must have measurable lesions according to the Response Evaluation Criteria in Solid Tumors (RECIST v1.1).
9\. ECOG performance score 0 or 1. 10. Prior anti-tumor treatment-related AEs (NCI-CTCAE v5.0 Criteria) have recovered to ≤ Grade 1 (except alopecia, Grade 2 hypothyroidism, non-clinically significant or asymptomatic laboratory abnormalities).
11\. Organ function must meet the basic requirements. 12. Patients of childbearing potential must take effective contraceptive measures during the treatment and for 180 days after the last dose of treatment.
Exclusion Criteria:
* 1\. History of hypersensitivity to any component of MRG002 or history of hypersensitivity of ≥ Grade 3 to trastuzumab.
2\. Patients who have received ADC drugs, or prior taxane, gemcitabine, and pemetrexed for locally advanced or metastatic urothelial cancer; or have received investigational drugs from other clinical trials, chemotherapy, radiotherapy, targeted therapy, or immunotherapy within 4 weeks prior to the first dose; or have received Chinese medicine (herbal medicine) or Chinese patent medicine with anti-tumor indications within 2 weeks prior to the first dose; or have received strong CYP3A4 inhibitors within 2 weeks prior to the first dose or have current requirement of CYP3A4 inhibitors; or had major surgery within 4 weeks prior to the first dose without full recovery or planned surgery within 12 weeks after study treatment.
3\. Patients with clinical symptoms such as plural, abdominal or pericardial effusion requiring puncture drainage.
4\. Patients with central nervous system (CNS) metastasis and/or neoplastic meningitis.
5\. Any severe or uncontrolled systemic diseases. 6. Patients with poorly controlled heart diseases. 7. Evidence of active infections, including but not limited to Hepatitis B, Hepatitis C, or human immunodeficiency virus (HIV) infection.
8\. History of other primary malignancies. 9. History of interstitial pneumonia, severe chronic obstructive pulmonary disease, severe pulmonary insufficiency, symptomatic bronchospasm, etc.
10\. Peripheral neuropathy greater than Grade 1. 11. History of cirrhosis. 12. Patients with active autoimmune disease or a history of autoimmune disease, who are using immunosuppressive agents, or systemic hormone therapy and still receiving them within 2 weeks prior to enrollment.
13\. Uncontrolled tumor-associated bone pain or urgent spinal cord compression. Patients requiring pain control must have been on a stable treatment regimen for at least 2 weeks at the time of first dose 14. Other conditions inappropriate for participation in this clinical trial, at the discretion of the investigator.
