A randomized controlled trial to compare antireflux metal stent and conventional covered metal stent for recurrent obstruction of covered metal stent for 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. Covered metal stent was occluded due to the duodenobiliary reflux within 90 days of stent placement, and cholantitis subsided via endoscopic biliary drainage 4. Irrespective of sex and a primary disease 5. Written informed consent obtained