A randomized controlled trial to compare antireflux metal stent and conventional covered metal stent for nonresectable distal malignant biliary obstruction

INTERVENTION: Endoscopic placement of antireflux metal stent for biliay obstruction Endoscopic placement of conventional covered metal stent for biliay obstruction CONDITION: Nonresectable distal malignant biliary obstruction PRIMARY OUTCOME: Time to recurrent biliary obstrution after the placement of metal stent INCLUSION CRITERIA: 1. nonresectable malignant biliary obstruction 2. distal biliary obstruction (2 cm or longer from the bifurcation) 3. Without a history of biliary SEMS placement 4. Irrespective of sex and a primary disease 5. Written informed consent obtained