Inclusion Criteria:
- Males or females aged ≥18 years;
- Histologically confirmed HER2-positive metastatic biliary tract cancer;
- ECOG performance status of 0 to 1;
- No prior treatment with anti-HER2 therapies;
- Patients have not received any systemic anticancer treatment in the recurrent/metastatic setting;
- Patients who have experienced disease recurrence more than 6 months after curative surgery; if adjuvant therapy (chemotherapy and/or radiotherapy) was received post-surgery, patients must have had recurrence more than 6 months after completion of adjuvant therapy;
- Presence of at least one measurable lesion;
- Adequate function of major organs as defined by the following criteria;
- Estimated survival of ≥3 months;
- Voluntary participation in this study, signing of the informed consent form, good compliance, and willingness to cooperate with follow-up.
Exclusion Criteria:
- Known allergy or contraindication to any component of the study drugs;
- Previous treatment with anti-HER2 therapies;
- Prior use of immunotherapy;
- Use of immunosuppressive agents within 14 days before the first dose, except:
Intranasal, inhaled, topical steroids, or local injections (e.g., intra-articular) Systemic corticosteroids ≤10 mg/day prednisone or equivalent Steroids for hypersensitivity reactions (e.g., premedication for CT scans)
- Known active central nervous system metastases or carcinomatous meningitis;
- Other malignancies within 5 years, excluding cured cervical carcinoma in situ, basal cell carcinoma, or squamous cell skin cancer;
- Major surgery or significant trauma within 4 weeks before randomization, or planned major surgery;
- Severe cardiac disease;
- Resting dyspnea due to tumor progression or comorbidities, or requiring supplemental oxygen;
- Neuropathy ≥ Grade I per NCI criteria;
- Active interstitial lung disease (ILD) or pulmonary disease requiring bronchodilators;
- History of immunodeficiency;
- Participation in another drug trial within 4 weeks before screening;
- Pregnant or breastfeeding women, or women of childbearing potential with a positive pregnancy test at screening; unwillingness to use effective contraception during and for 6 months after the study;
- Any serious concomitant illness or conditions that may interfere with the planned therapy or render participation unsuitable.