The study is a single-arm, phase II trial. The purpose is to investigate both the efficacy and safety of radiotherapy combined with anti-PD-1 antibody in unresectable biliary tract cancer patients.

The trial will recruit 36 patients, and they will undergo radiotherapy plus anti-PD-1 antibody. Patients will receive conventional intensity-modulated radiotherapy or stereotactic body radiation therapy first for a total dose more than 45Gy. Camrelizumab 200mg intravenously every 3 weeks will be initiated within 7 days after radiotherapy.

Inclusion Criteria:

1. Aged between 18 and 75 years old;
2. Histopathologically confirmed unresectable primary or initial postoperative recurrent BTC without distant metastasis;
3. No previous radiotherapy or systemic therapy;
4. Adequate volume of the uninvolved liver (larger than 700 mL);
5. At least one measurable lesion based on Response Evaluation Criteria in Solid Tumors 1.1 criteria;
6. Eastern Cooperative Oncology Group performance status score of 0 or 1;
7. Adequate hematologic (absolute neutrophil count ≥ 1.5x109/L, hemoglobin concentration ≥ 90g/L, platelet count ≥ 100 x109/L), hepatic (albumin ≥ 28 g/L, total bilirubin < 1.5 times the upper limit of normal (ULN), alanine aminotransferase and aspartate aminotransferase < 5×ULN) and renal function (serum creatine < 1.5×ULN, creatinine clearance rate ≥ 45ml/min);
8. Life expectancy of at least 12 weeks.

Exclusion Criteria:

1. Have acute or chronic active hepatitis B or C, HBV-DNA>2000IU/ml or 104 copy/ml; HCV-RNA>103 copy/ml; both HBsAg and HCV antibody are positive. If the related results become lower than above standards after anti-viral treatment, the patients are qualified for enrolment;
2. Have metastasis in extrahepatic distant organs including lung, central nervous system, bone and etc. Or extrahepatic lymph node metastasis beyond abdomen;
3. Have risky bleeding events requiring transfusion, operation or local therapies, continuous medication in the past 3 months;
4. Have thromboembolism in the past 6 months, including myocardial infarction, unstable angina, stroke or transient ischemic attack, pulmonary embolism, deep vein thrombosis;
5. Have taken aspirin (>325mg/day) or other antiplatelet drugs continuously for 10 days or more within 2 weeks before enrolment;
6. Uncontrollable hypertension, systolic pressure>140mmHg or diastolic pressure>90mmHg after best medical care, or history of hypertensive crisis or hypertensive encephalopathy;
7. Symptomatic congestive heart failure (NYHA class II-IV). Symptomatic or badly-controlled arrhythmia. Congenital long QT syndrome or modified QTc>500ms upon screening;
8. Have active autoimmune diseases that require systemic treatment within 2 years before enrolment;
9. Active tuberculosis, having antituberculosis therapy at present or within 1 year;
10. Have a known history of prior invasive malignancies within 5 years before enrolment;
11. Pregnant or breastfeeding women, or expecting to conceive or father children within the projected duration of the trial;
12. Have other uncontrollable comorbidities;
13. Infection of HIV, known syphilis requiring treatment;
14. Allergic to elements of camrelizumab.