Background: Despite complete resection, disease-free survival (DFS) of patients with cholangiocarcinoma (CCA) is less than 65% after one year and not more than 35% after three years. For muscle invasive gallbladder carcinoma (GBCA), prognosis is even worse, with an overall survival (OS) of only 30% after three years. Thus, evaluation of adjuvant chemotherapy in biliary tract cancer in a large randomized trial is warranted. Methods/Design: ACTICCA-1 is a randomized, multidisciplinary, multinational phase III investigator initiated trial. With respect to data obtained in the ABC-02 trial, we selected the combination of gemcitabine and cisplatin for 24weeks as investigational treatment. Based on adjuvant trials in pancreatic cancer with comparable postoperative recovery time, inclusion of patients within a maximum interval of 16weeks between surgery and start of chemotherapy was stipulated. Due to the different prognosis and treatment susceptibility of muscle invasive carcinoma, two separate cohorts (CCA and GBCA) were included to capture the potentially different treatment effects. Randomization is stratified for lymph node status for both cohorts and localization for CCA. The primary endpoint is DFS and secondary endpoints include OS, safety and tolerability of chemotherapy, quality of life, and patterns of disease recurrence. For CCA, adjuvant chemotherapy should increase DFS 24months post-surgery from 40 to 55% to be considered relevant. With a power of 80% and a significance level of 5%, 271 evaluable study patients have to be followed for 24-28 months to observe 166 events. For GBCA, chemotherapy should increase DFS 24months post-surgery from 35 to 55% to be of relevance; thus, 154 evaluable study patients have to be monitored for 24-28 months to observe 90 events. In both cohorts, randomization will be 1:1 with chemotherapy for 24weeks and imaging every twelve weeks. In 2014, the study was initiated in Germany and in The Netherlands (funded by the Deutsche Krebshilfe, the Dutch Cancer Society, and supported ...