Background: Despite improvements in multidisciplinary management, patients with biliary tract cancer (BTC) have a poor outcome. Only 20% of patients are eligible for surgical resection with curative intent, with 5-year overall survival of less than 10% for all patients. Data regarding pure adjuvant chemotherapy in BTC’s are conflicting and the SOC of the western world is currently capecitabine according to the British BILCAP- trial, even though BILCAP was formally negative. Based on the positive data for durvalumab in the TOPAZ- 1 – trial in BTC and for STRIDE- regimen in HCC according to the Himalaya- data, evaluation of IO- combination in the adjuvant setting seems to be promising. Preclinical studies indicate that the antibody combination results in stronger and more durable anti-tumor effects than single therapies by synergistically modulating the immunosuppressive tumor microenvironment which is particularly rich in cholangiocarcinoma. The aim of this study is the assessment of the clinical activity of the anti-PD-L1 (programmed- death 1-ligand) antibody durvalumab and the anti-CTLA-4 (cytotoxic T- lymphocyte-associated antigen 4) antibody tremelimumab in combination with or without capecitabine in patients with respectable BTC in the adjuvant situation. This is a randomized phase II study as a proof-of-concept for a potentially larger research program. Methods: The ADJUBIL trial is an open-label, multicenter phase II study, including patients with BTC after curative surgery with no previous systemic treatment. Patients are randomly assigned to receive tremelimumab (300mg, one dose) plus durvalumab (1500mg every 4 weeks; STRIDE, for a maximum of 12 months), with or without capecitabine (for 8 cycles). Forty evaluable patients will be enrolled in the study (1:1) to receive anticancer treatment until disease recurrence or intolerable toxicities. Primary objective is to assess the anti-tumor activity of the treatment in both arms by the recurrence-free survival rate after 12 months (RFS@12). Secondary endpoints are recurrence-free survival, overall survival, toxicity, and quality of life. Exploratory endpoints: Explore predictive biomarkers for recurrence-free survival and overall survival. Study start of the ADJUBIL trial was in June 2021. By January 2023, 12 centers across Germany have been initiated and a total of 8 out of 40 planned patients (1:1) have been enrolled. The study is currently ongoing. Clinical trial information: EUCTR2021-002389-41.