The purpose of this study is to compare the duration of stent patency between partially covered and fully covered SEMS for palliation of malignant distal bile duct obstruction.

Endoscopic stent placement has been used as a principle palliative method in patients with unresectable distal malignancy biliary obstruction. It has been pivotal in providing relief from obstructive jaundice, improving the quality of life, and allowing the maintenance of chemotherapy. Although SEMSs have been reported to be superior to plastic stents in terms of stent patency, they still have some debatable issues ; in uncovered SEMS, stent occlusion due to epithelial hyperplasia and tumor ingrowth through the metal mesh is a frequent problem, whereas covered SEMSs are prone to migration.

The aim of the current study is to compare the duration of stent patency between partially covered and fully covered SEMS as a primary objective, and investigate overall patient survival, stent occlusion rate, and incidence of adverse events including stent dysfunction as secondary objectives.

Inclusion Criteria:

• 1.> 19years 2.malignant biliary obstruction, 2 cm distal to hilum 3.unsuitable for curative surgical resection owing to metastasis, locally advanced stage, high operation risk, or patient's refusal

Exclusion Criteria:

• 1.history of biliary surgery except cholecystectomy 2.history of SEMS placement 3.coagulopathy (INR>1.5, Platelet<50000) 4.expected survival > 3 months based on Karnofsky performance score 5.duodenal stricture