Metallic stents are commonly used for biliary drainage in patients with unresectable malignant distal biliary obstruction. However, it is unclear whether a 12-mm partially covered self-expandable metallic stent or a 12-mm bare self-expandable metallic stent provides better effectiveness and safety. This prospective, randomized clinical trial will compare these two stent types in adult patients who have already undergone percutaneous transhepatic biliary drainage (PTBD) and are scheduled for metallic stent placement through the existing PTBD tract. A total of 60 participants will be enrolled. After stent placement, participants will be followed for 12 months, with assessments at 3, 6, and 12 months. The study will evaluate recurrent biliary obstruction, stent patency duration, reintervention, overall survival, and procedure-related complications. The results are expected to provide evidence for selecting the most appropriate 12-mm metallic stent for patients with unresectable malignant distal biliary obstruction.

Malignant distal biliary obstruction is commonly caused by pancreatic cancer, cholangiocarcinoma, gallbladder cancer, or metastatic malignancy. In patients with unresectable disease, biliary drainage with a self-expandable metallic stent is widely used as palliative treatment. Bare metallic stents have the advantage of firm fixation, but tumor ingrowth can lead to recurrent biliary obstruction. Covered metallic stents may reduce tumor ingrowth, but concerns remain regarding stent migration and other procedure-related complications. Although 10-mm stents have been studied previously, evidence remains limited regarding the comparative effectiveness and safety of 12-mm partially covered versus bare self-expandable metallic stents.

This study is a prospective, single-center, randomized clinical trial designed to compare a 12-mm partially covered self-expandable metallic stent with a 12-mm bare self-expandable metallic stent in patients with unresectable malignant distal biliary obstruction. Adult patients who have already undergone percutaneous transhepatic biliary drainage (PTBD) according to the institutional clinical protocol and are scheduled for metallic stent placement through the existing PTBD tract will be screened for eligibility. After written informed consent is obtained, eligible participants will be randomly assigned in a 1:1 ratio to receive either a 12-mm partially covered self-expandable metallic stent or a 12-mm bare self-expandable metallic stent.

All procedures will be performed through a percutaneous transhepatic approach using the existing PTBD tract. After assessment of the biliary stricture, an appropriately sized 12-mm metallic stent will be placed. Participants will be followed for 12 months after stent placement, with follow-up assessments at 3, 6, and 12 months. The primary outcome is the cumulative incidence of recurrent biliary obstruction within 12 months after the procedure. Secondary outcomes include time to recurrent biliary obstruction, overall recurrent biliary obstruction rate, causes of recurrent biliary obstruction, reintervention, overall survival, and procedure-related complications such as pancreatitis, cholecystitis, bleeding, perforation, and cholangitis. The results of this study are expected to provide evidence to guide selection of the most appropriate 12-mm metallic stent in patients with unresectable malignant distal biliary obstruction.

Inclusion Criteria:

• Patients who voluntarily provide written informed consent after receiving sufficient explanation of the study purpose, methods, and potential benefits and risks
• Adults aged 19 years or older
• Patients diagnosed with unresectable malignant distal biliary obstruction based on imaging studies (CT, MRI, ERCP, etc.) or histologic confirmation
• Patients who have already undergone percutaneous transhepatic biliary drainage (PTBD) according to the institutional clinical protocol and are scheduled for metallic stent placement through the existing PTBD tract

Exclusion Criteria:

• Patients with a previous history of biliary metallic stent placement
• Patients with upper biliary obstruction (hilar level or above)
• Patients with other major biliary lesions in addition to malignant distal biliary obstruction
• Patients for whom the investigator judges that study conduct or data collection would be markedly difficult

Participants will be unaware of the type of stent inserted, whereas treating investigators will not be masked because they perform the procedure.