Neoadjuvant Gemcitabine Plus Cisplatin With or Without Durvalumab in Resectable Biliary Tract Cancer

Inclusion Criteria: * Capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol. * Age \> 19 years at time of study entry * Histologically confirmed adenocarcinoma of biliary tract (intrahepatic, hilar or extrahepatic cholangiocarcinoma, or gallbladder carcinoma). * Localized, potentially resectable, non-metastatic disease (determined at the discretion of attending surgeons) based on the results of CT, MRI or PET-CT scans. * No active uncontrolled infection, except chronic viral hepatitis under antiviral therapy. * Eastern Cooperative Oncology Group (ECOG performance status of 0 or 1 * Body weight \>30kg * Adequate normal organ and marrow function * Patient is willing and able to comply with the protocol for the duration of the study including undergoing treatment and scheduled visits and examinations including follow up. * No other malignant disease apart from non-melanotic skin cancer, carcinoma in situ of the uterine cervix, localized prostate or papillary thyroid cancer, or any other cancer where treated with curative intent \> 5 years previously without evidence of relapse Exclusion Criteria: * Medical or psychiatric conditions that compromise the patient's ability to give informed consent or to complete the protocol or a history of non-compliance * Obstruction of gastrointestinal tract * Active gastrointestinal bleeding * Myocardial infarction within 6 months prior to the study medication, and other clinically significant heart disease (e.g., unstable angina, congestive heart failure or uncontrolled hypertension) * Evidence of severe or uncontrolled systemic disease or any concurrent condition which in the investigator's opinion makes it undesirable for the patient to participate in the study or which would jeopardise compliance with the protocol * Combined hepatocellular carcinoma/cholangiocarcinoma is excluded. * History of allogenic organ transplantation. * History of another primary malignancy except for 1. Malignancy treated with curative intent and with no known active disease ≥5 years before the first dose of IP and of low potential risk for recurrence 2. Adequately treated non-melanoma skin cancer or lentigo maligna without evidence of disease 3. Adequately treated carcinoma in situ without evidence of disease * Mean QT interval corrected for heart rate using Fridericia's formula (QTcF) ≥470 ms calculated from 3 ECGs (within 15 minutes at 5 minutes apart). * Female patients who are pregnant or breastfeeding or male or female patients of reproductive potential who are not willing to employ effective birth control from screening to 90 days after the last dose of durvalumab monotherapy. * Known allergy or hypersensitivity to any of the study drugs or any of the study drug excipients. * Judgment by the investigator that the patient is unsuitable to participate in the study and the patient is unlikely to comply with study procedures, restrictions and requirements.