To evaluate the efficacy and safety of inetetamab in combination with chemotherapy ± immunotherapy as a first-line treatment for HER2-positive advanced biliary tract cancer, providing theoretical evidence and practical guidance for further optimizing treatment regimens and improving therapeutic outcomes.

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.