Comparative performance of uncoated, self-expanding metal biliary stents of different designs in 2 diameters: final results of an international multicenter, randomized, controlled trial

BackgroundThe Wallstent has remained the industry standard for biliary self-expanding metal stents (SEMSs). Recently, stents of differing designs, compositions, and diameters have been developed.ObjectiveTo compare the new nitinol 6-mm and 10-mm Zilver stents with the 10-mm stainless steel Wallstent and determine the mechanism of obstruction.DesignRandomized, prospective, controlled study.SettingNine centers experienced in SEMS placement during ERCP.PatientsA total of 241 patients presenting between September 2003 and December 2005 with unresectable malignant biliary strictures at least 2 cm distal to the bifurcation.Main Outcome MeasurementStent occlusions requiring reintervention and death.ResultsAt interim analysis, a significant increase in occlusions was noted in the 6-mm Zilver group at the P = .04 level, resulting in arm closure but continued follow-up. Final study arms were 64, 88, and 89 patients receiving a 6-mm Zilver, 10-mm Zilver, and 10-mm Wallstent, respectively. Stent occlusions occurred in 25 (39.1%) of the patients in the 6-mm Zilver arm, 21 (23.9%) of the patients in the 10-mm Zilver arm, and 19 (21.4%) of the patients in the 10-mm Wallstent arm (P = .02). The mean number of days of stent patency were 142.9, 185.8, and 186.7, respectively (P = .057). No differences were noted in secondary endpoints, and the study was ended at the 95% censored study endpoints. Biopsy specimens of ingrowth occlusive tissue revealed that 56% were caused by benign epithelial hyperplasia.ConclusionsSEMS occlusions were much more frequent with a 6-mm diameter SEMS and equivalent in the two 10-mm arms despite major differences in stent design, material, and expansion, suggesting that diameter is the critical feature. Malignant tumor ingrowth produced only a minority of the documented occlusions.