Patient description: A 54-year-old obese woman admitted to the emergency department with abdominal pain that started 4 days ago with nausea and vomiting. The epigastric pain radiates to the right upper quadrant, getting worse after eating fatty food. The patient experienced similar pain twice in the past year. Her past medical history is remarkable for hypercholesterolemia and 2 NVDs. She has 2 children, and she is menopausal. She does not smoke, drink alcohol, or use illicit drugs. She is mildly febrile. Her BP is 150/85, HR 115, RR 15, T 38.2, SpO2 98% on RA. She is an obese woman with no acute distress. On palpation, she experiences epigastric tenderness and tenderness in the right upper quadrant without rebound. Bowel sounds are normal. Laboratory analysis is remarkable for elevated ESR and leukocytosis with a left shift. The ultrasound revealed several gallstones, biliary sludge and CBD stones. The smallest stone is 14mm.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Advanced Biliary Tract Cancer Subjects must meet all of the following Subjects volunteer to participate in the study and agree to sign the informed consent with good compliance and follow-up Subjects are 18 years old or older when signing the informed consent and gender is not limited Subjects were diagnosed with advanced biliary tract cancers by imaging and histological examination, including intrahepatic cholangiocarcinoma, hilar cholangiocarcinoma, common bile duct cancer and gallbladder cancer. Advanced biliary tract cancers refer to unresectable, recurrent, locally advanced and metastatic lesions which are defined as stage IIIA or above according to the 8th AJCC stage system The disease is not suitable for radical surgery and/or topical treatment, or disease progression occurs after surgery and/or local treatment, including lesion resection, ablation, transcatheter arterial chemoembolization (TACE), hepatic arterial infusion chemotherapy (HAIC), radiotherapy at least 4 weeks before the baseline assessment. All acute toxic effects of local treatment must be ≤ CTCAE 5.0 Level 1 Patients are intolerant or fail after first-line systemic treatment (gemcitabine or platinum based regimen) and require palliative treatment. The first-line system treatment failure was ≥ 1 month before enrollment in this study (signing informed consent) and adverse events are controlled (NCI-CTCAE ≤ Grade Ⅰ). i) Definition of systemic treatment: Gemcitabine or platinum based regimen for more than 1 cycle. Adjuvant chemotherapy based on gemcitabine or platinum is considered as first-line treatment if recurrence occur during or after 6 months adjuvant chemotherapy sequential to tumor resection. ii) Definition of treatment failure: Disease progression occur during treatment or in 6 months after the last cycle. iii) Definition of intolerance: Grade ≥IV hematologic toxicity; grade ≥III toxicity of liver, kidney and skin; grade ≥ II toxicity of heart, lung and brain Prior treatment must not lenvatinib, PD-1 / PD-L1 antibodies or molecular targeted therapy for ≥ 14 days At least one measurable lesion (according to version 1.1): the measurable lesion has a long diameter ≥ 10 mm or lymphadenopathy has a short diameter ≥ 15 mm in spiral CT scan Blood pressure is controlled <= 150/90 mmHg with no more than 3 antihypertensive drugs The ECOG score is 0-1 within 1 week before enrollment  Subjects with one or more than one of the following should be excluded Patients meet with any of the following condition: Suitable for radical surgery; Or, without an assessment lesion after radical surgery; Or, never receive any first line treatment Patients who received first-line chemotherapy within 1 month when participating in the study Already known to be allergic or intolerant to recombinant humanized PD-1 monoclonal antibody drugs (or components) or lenvatinib Previously received with lenvatinib, or any anti-vascular endothelial growth factor (VEGF) or VEGF receptor targeted drug, or any anti-PD-1, anti-PD-L1 or anti-PD-L2 or CTLA-4 drug, including antibodies involved in JS001 clinical studies ECOG score ≥ 2 points Hepatic encephalopathy Histopathological result show mixed liver cancer, squamous cell carcinoma or sarcoma cell component More than 2 organs metastasis, including liver, lung, bone and brain pregnant women (positive pregnancy test before taking the drug) or lactating women