Pembrolizumab With or Without Lenvatinib or Chemotherapy in First-Line Treatment of Advanced Biliary Tract Cancer

Inclusion Criteria: * • The subjects voluntarily participate in the study and agree to sign the informed consent form, are compliant, and cooperate with follow-up. * They are over 18 years of age and gender is not restricted when signing the informed consent form. * They have histologically confirmed unresectable advanced or metastatic biliary tract adenocarcinoma, including intrahepatic or extrahepatic cholangiocarcinoma and gallbladder cancer. * Patients who are diagnosed with unresectable or metastatic disease and have not received prior treatment are eligible for inclusion. * Patients who have undergone curative surgery and experienced disease recurrence after more than 6 months; or patients who have completed adjuvant therapy (chemotherapy and/or radiotherapy) and have been disease-free for more than 6 months after completing adjuvant therapy are eligible for inclusion. * They have at least one measurable lesion (as defined by RECIST 1.1, the measurable lesion is a spiral CT scan long diameter ≥10mm or lymph node short diameter ≥15mm). * Their ECOG score is 0-1 in the week prior to enrollment. * Based on the investigator's assessment, their estimated survival time is ≥3 months. * Patients with active hepatitis B or C require relevant antiviral treatment, with HBV-DNA \<2000 IU/ml (\<104 copies/ml), and have received at least 14 days of antiviral treatment before participating in the study. HCV RNA-positive patients must follow local standard treatment guidelines for antiviral therapy, and their liver function is within CTCAE Grade 1 elevation. * Their hematological and organ functions are adequate, based on laboratory test results obtained within 14 days before the start of the study (unless otherwise specified): * Hematology: (no blood transfusion, no G-CSF, no drug correction within 14 days prior to screening) Hb ≥90 g/L; neutrophil count ≥1.5×109/L; PLT ≥100×109/L. * Biochemistry: (no albumin transfusion within 14 days) Appropriate liver function: ALT and AST ≤2.5×ULN; for patients with liver metastases, ALT and AST ≤5 × ULN. Serum bilirubin ≤2.0×ULN; these conditions do not apply to patients with confirmed Gilbert's syndrome. Any clinically significant biliary obstruction should be resolved before randomization. Appropriate renal function: creatinine ≤1.5×ULN, or creatinine clearance rate (CCr) \>50mL/min (using the standard Cockcroft-Gault formula): Female: CrCl = ((140 - age) x weight (kg) x 0.85) / 72 x serum creatinine (mg/ dL) Male: CrCl = ((140 - age) x weight (kg) x 1.00) / 72 x serum creatinine (mg/ dL) * Women of childbearing potential: agree to abstain from sexual intercourse or use contraceptive methods with a failure rate of less than 1% during the treatment period and for at least 6 months after the last dose. If a female patient has menstruation and has not reached menopause (continuous absence of menstruation for ≥12 months without other reasons), and has not undergone sterilization surgery (removal of ovaries and/or uterus), she is considered to be of childbearing potential. Examples of contraceptive methods with a failure rate of less than 1% include bilateral tubal ligation, male sterilization, hormone-based contraceptives that inhibit ovulation, hormone-releasing intrauterine devices, and copper intrauterine devices. The reliability of sexual restraint should be evaluated relative to the duration of the clinical trial and the patient's preferred lifestyle and daily routine. Periodic abstinence (such as calendar day, ovulation period, symptom temperature, or post-ovulation method) and ejaculation outside the vagina are unacceptable contraceptive methods. * Male: agree to abstain from sexual intercourse or use contraceptive measures, agree not to donate sperm, as defined below: When the female partner is of childbearing potential, male patients must abstain during the treatment period and for 6 months after the last dose, or use a condom plus other contraceptive methods to achieve a failure rate of less than 1%. Male patients must also agree not to donate sperm during the same period. When the female partner is already pregnant, male patients must abstain or use a condom to prevent fetal exposure to the study during the treatment period and for 6 months after the last dose. The reliability of sexual restraint should be evaluated relative to the duration of the clinical trial and the patient's preferred lifestyle and daily routine. Periodic abstinence (such as calendar day, ovulation period, symptom temperature, or post-ovulation method) and ejaculation outside the vagina are unacceptable contraceptive methods. Exclusion Criteria: * • Previous systemic treatment received. * ECOG score \> 1. * Pancreatic cancer. * Pregnant (positive pregnancy test before medication) or breastfeeding women. * Known allergy or intolerance to recombinant humanized PD-1 monoclonal antibody drugs, lenvatinib and its components (or any excipients). * Received local anti-tumor treatment within 4 weeks before the first study drug treatment, including but not limited to surgery, radiotherapy, hepatic artery embolization, TACE, hepatic artery infusion, radiofrequency ablation, cryoablation, or percutaneous ethanol injection (allowing palliative radiotherapy for bone metastases at least 2 weeks before study drug treatment). * Previous or existing grade 3 or higher gastrointestinal fistula or non gastrointestinal fistula (such as skin) according to CTCAE 5.0 criteria. Multiple factors affecting oral administration of lenvatinib (such as inability to swallow, chronic diarrhea and intestinal obstruction, or other conditions that significantly affect drug intake and absorption). * Major surgery (except biopsy) has been performed within 4 weeks before the first study drug treatment, or the surgical incision has not completely healed; minor surgery (such as simple excision, biopsy, etc.) was performed within 7 days before the first study inter