6-mm versus 10-mm covered self-expandable metal stents and plastic stents for malignant distal biliary obstruction in resectable or borderline resectable pancreatic cancer in Japan (STARDOM, JON-2402P): study protocol for a multicenter randomized con

BACKGROUND: Pancreatic cancer is one of the most lethal malignancies; patients with resectable (R) or borderline resectable (BR) disease are treated with neoadjuvant chemotherapy (NAC) followed by surgery. In those with distal biliary obstruction, preoperative biliary drainage enables the timely initiation and completion of NAC followed by surgery. The optimal stent type remains undetermined; 10-mm covered self-expandable metal stents (CSEMS) provide long patency but increase the risk of cholecystitis and pancreatitis, whereas plastic stents (PS) are safer but have shorter patency. A 6-mm CSEMS potentially offers a balanced option that reduces adverse events while maintaining patency during the preoperative period. The STARDOM trial is designed to determine whether 6-mm CSEMS can maintain stent patency while reducing adverse events in preoperative biliary drainage for R/BR pancreatic cancer with distal biliary obstruction. METHODS: In a multicenter, open-label, three-arm superiority randomized controlled trial at 89 institutions across Japan, including academic hospitals and high-volume referral centers, 330 adult patients (≥ 18 years) with R/BR pancreatic cancer and distal biliary obstruction requiring preoperative biliary drainage will be recruited by investigators at each participating institution and randomly assigned (1:1:1) to receive either a 10-mm CSEMS, PS (7Fr or 8.5Fr), or 6-mm CSEMS. Patients with severe acute cholangitis or gastrointestinal obstruction will be excluded. Randomization will be stratified by institution, resectability status, and history of cholecystectomy. The primary endpoint is the event-free survival proportion at 12 weeks, defined as the absence of stent-related events including recurrent biliary obstruction (RBO), pancreatitis, cholecystitis, non-occlusive cholangitis, gastrointestinal bleeding, aspiration pneumonia, liver abscess, perforation, or death. Secondary endpoints include the event incidence rate at 12 weeks, event-free survival proportion, and event incidence rate at 12 and 24 weeks in R and BR patients, respectively; the proportion and incidence rate of each primary endpoint component; technical and clinical success; re-intervention success; and surgical outcomes such as surgical resection proportion, operative time, blood loss, postoperative complications, hospital stay, R0 resection proportion, vascular invasion, and lymph node metastasis. DISCUSSION: The STARDOM trial is a nationwide multicenter randomized controlled study to directly compare 6-mm CSEMS with conventional 10-mm CSEMS and PS in the pancreatic cancer preoperative setting. Clarifying the optimal drainage method potentially improves perioperative safety, ensures uninterrupted NAC, and supports better oncosurgical outcomes in patients with R/BR pancreatic cancer. TRIAL REGISTRATION: Japan Registry of Clinical Trials (jRCT ID: jRCT1042250093; registered on August 9, 2025). Trial registry URL: https://jrct.mhlw.go.jp/latest-detail/jRCT1042250093. First planned enrollment: August 25, 2025.