Reply to Dr. Köker

We thank Dr. Köker for his interest in our work. He has questioned why we used uncovered self-expendable metallic stents (SEMSs) rather than covered SEMSs. He also raises the possibility of selection bias with regard to the difference in baseline characteristics of the two groups in our study.

First, in hepatocellular carcinoma patients and also in our study patients, the majority of biliary obstructions involve the hilar or intrahepatic bile ducts. Covered SEMSs should not be used across the hilar bile duct because these large-bore covered stents could obstruct the bile duct draining the opposite side of the liver, which was originally not involved. The references which Dr. Köker presents include solely patients with distal bile duct obstruction and not those with hilar or intrahepatic bile duct obstruction [1] [2].

Moreover, there is no strong evidence that covered SEMSs are superior to uncovered SEMSs, even in distal bile duct obstruction. Recent studies have reported that there were no significant differences in stent patency or in the patients’ survival between covered and uncovered SEMSs [3] [4]. In the most recent meta-analysis [5], the tumor ingrowth rates were lower in the covered SEMS groups than in the uncovered SEMS groups (odds ratio [OR] 0.19; 95 % confidence interval [CI] 0.07 – 0.55), but the rates of tumor overgrowth (OR 1.88; 95 %CI 1.02 – 3.45) and migration (OR 7.13; 95 %CI 2.29 – 22.21) were higher. Furthermore, the stent patency and patients’ survival data were not significantly different. Considering that a frequent cause of stent malfunction in patients with hepatocellular carcinoma is hemobilia and tumor thrombus, the benefit of covered SEMSs (less tumor ingrowth) could be reduced. Therefore, uncovered SEMSs would seem more appropriate for our patients than covered SEMSs.

Second, as Dr. Köker mentioned and we noted in our article, our study was performed retrospectively, so the possibility of selection bias is inevitable. Also, the baseline characteristics of the patients in our study were different between the two groups, and cancer stage and the presence of portal vein invasion could act as confounders for patients’ survival. However, the stent type (plastic or metal) was a significant factor, even in multivariate analysis, and therefore we consider our results to be sufficiently meaningful in spite of these limitations.

• References

• 1 Isayama H, Komatsu Y, Tsujino T et al. A prospective randomised study of “covered” versus “uncovered” diamond stents for the management of distal malignant biliary obstruction. Gut 2004; 53: 729-734
• 2 Petersen BT, Kahaleh M, Kozarek RA et al. A multicenter, prospective study of a new fully covered expandable metal biliary stent for the palliative treatment of malignant bile duct obstruction. Gastroenterol Res Pract 2013; 2013: 642428
• 3 Lee JH, Krishna SG, Singh A et al. Comparison of the utility of covered metal stents versus uncovered metal stents in the management of malignant biliary strictures in 749 patients. Gastrointest Endosc 2013; 78: 312-324
• 4 Ung K-A, Stotzer P-O, Nilsson Å et al. Covered and uncovered self-expandable metallic Hanarostents are equally efficacious in the drainage of extrahepatic malignant strictures. Results of a double-blind randomized study. Scand J Gastroenterol 2013; 48: 459-465
• 5 Almadi MA, Barkun AN, Martel M. No benefit of covered vs uncovered self-expandable metal stents in patients with malignant distal biliary obstruction: a meta-analysis. Clin Gastroenterol Hepatol 2013; 11: 27-37. e21