Prophylactic endoscopic transpapillary gallbladder stenting at fully covered self-expandable metal stent placement to prevent cholecystitis in malignant distal biliary obstruction: A multicenter prospective single-arm study protocol (PROTECT study)

BACKGROUND: Malignant distal biliary obstruction (MDBO) is commonly managed with endoscopic retrograde cholangiopancreatography (ERCP)-guided transpapillary stenting. Fully covered self-expandable metal stents (FCSEMSs) provide durable biliary drainage but may increase the risk of acute cholecystitis due to cystic duct obstruction. Prophylactic endoscopic transpapillary gallbladder stenting (ETGBS) at the time of FCSEMS placement has been proposed to reduce the risk of cholecystitis after FCSEMS placement. However, the available evidence is limited. This study aims to explore the potential clinical benefit of attempting prophylactic ETGBS by estimating the incidence of acute cholecystitis after FCSEMS placement and characterizing the technical feasibility and safety of the strategy in patients with MDBO. METHODS: This multicenter, prospective, single-arm exploratory study (PROTECT study) will be conducted at four institutions in Japan. In all eligible patients undergoing FCSEMS placement for MDBO, prophylactic ETGBS will be attempted. The primary endpoint is the incidence of acute cholecystitis within 30 days after FCSEMS placement. Secondary endpoints include the technical success rate of ETGBS, procedure-related adverse events, the incidence of acute cholecystitis within 30 days among patients with technically successful ETGBS, and the cumulative incidence of acute cholecystitis from day 31 until the end of follow-up. The target enrollment is 50 patients. The primary endpoint will be summarized as a proportion with a two-sided 90% Wilson score confidence interval. A two-sided 95% Wilson score confidence interval will also be reported as a supplementary analysis, and a supplementary exploratory two-sided one-sample score test will compare the observed proportion with the historical benchmark of 12.1%. DISCUSSION: This study will provide prospective data on the potential clinical utility, technical feasibility, and safety of attempting prophylactic ETGBS and may inform the design of future comparative studies. TRIAL REGISTRATION: Japan Registry of Clinical Trials number: jRCT1030250361. Registered on 12 September 2025.