Choosing the Metal Biliary Stent Type for Palliation of Neoplastic Stenosis during Endoscopic Retrograde Cholangiopancreatography

Biliary stenting is a well-established treatment for unresectable neoplastic biliary stenosis. Unfortunately, however, there is as yet no consensus regarding the choice of the appropriate stent type relative to the patient or the stenosis. Many types of plastic stent are available, and reports have compared these without establishing any significant differences. When the metal biliary stent first became available 10 years ago, it was enthusiastically welcomed. Some reports have described advantages in the durability of metal stents in comparison with plastic ones, but the principal indication for metal stents is still in patients who have an anticipated survival period of more than 3 - 6 months [1]. Although many types of metallic biliary stent are now available, it is not known which type is best able to improve cost-effectiveness and quality of life, since criteria for choosing stents are lacking. Only a few papers so far have reported experience with a single type of metal biliary stent, or have compared two types of metal biliary stent. The paper by Ahmad et al., published in a recent issue of Endoscopy, was therefore welcome, as it addressed a very important topic in the clinical practice of therapeutic endoscopy [2]. The paper reports experience with two types of metal biliary stent - the Ultraflex Diamond stent and the biliary Wallstent. The Ultraflex metal stent had a similar occlusion rate to the Wallstent, but the time to occlusion and the patency period were poorer than with the Wallstent and were quite similar to those of plastic stents. I read the paper with great interest and would like to make some comments on it.

The authors collected prospective data from a group of 32 patients who underwent stenting with an Ultraflex Diamond metal biliary stent, excluding data for 11 patients for reasons that were stated; data from only 21 patients were assessed and compared with those obtained retrospectively from a group of patients treated with biliary Wallstents 1 year previously. The method of obtaining data was very different in the two groups: in the first group, data were gathered prospectively, with clinical routine and biochemical follow-up, while in the second group they were collected retrospectively from telephone interviews as much as 1 year after the biliary stenting procedure, and also from a retrospective review of medical records. A selection bias is present, but not only for inclusion in the Wallstent group of patients with a better outcome, as the authors themselves stated.

Data for 11 of the 32 patients in the Ultraflex cohort were excluded for various stated reasons, whereas data for 11 of the 30 patients in the Wallstent group were excluded only because they were not reliable. Exclusion from the Ultraflex group was determined by very serious conditions, such as bilateral hilar stenting or previous occlusion of a metal stent - conditions that are not reported in the Wallstent cohort. This might suggest more extensive experience in the endoscopic team, who might at this time have been carrying out stenting procedures in much more difficult cases than previously. The fact that the Ultraflex cohort may have included more patients with serious conditions is also suggested by the numbers of patients who had previously received plastic stents: 10 of 19 in the Wallstent group, compared with 14 of 21 in the Ultraflex group. However, previous clogging of a plastic stent is a risk factor that shortens the patency period in metal stents [3]. In addition, in nine of the 19 patients in the Wallstent group and seven of the 21 in the Ultraflex group, the metal stent was the stent of choice at the index endoscopic retrograde cholangiopancreatography (ERCP). Since the main indication today for preferring a metal stent to a plastic one is an anticipated survival beyond 3 - 6 months, the patients in the Wallstent group may have had a better prognosis than the patients in the Ultraflex group. The patients in the Ultraflex group may have had more advanced neoplasia and a lower life expectancy than the other group, as judged at index ERCP by the authors themselves.

Initial placement of a metal stent results in a longer period of stent patency than initial placement of a plastic one; a longer initial patency period appears to improve patient compliance, which in turn results in a reduction in the number of patients dying with untreated stent occlusion [4]. Can the authors indicate whether there were any differences in compliance between the two groups of patients and report what their policy was in case of occlusion of metal stents? Another relevant point with regard to differences in the anticipated survival between the two groups is the fact that despite different follow-up periods (at least 1 year of difference), the same numbers of patients were alive with a patent stent in both groups; more interestingly, a similar number of patients died without jaundice as with a patent stent. In addition, many patients in the Wallstent group survived well over a year - a very unusual survival period for patients with a neoplastic biliary stenosis due to pancreatic or gallbladder cancer [1]. Can the authors report what the incidence of duodenal stenosis was in the two groups, as duodenal invasion can indicate more advanced disease; what the incidence of gallbladder cancer was, if any, in the two cohorts of patients; and whether they attempted any histological diagnosis of the biliary stenoses that were treated?

The mean age of patients was also greater, and with a smaller standard deviation, in the Ultraflex group, so that this group must have included a larger number of older patients and presumably patients with more advanced neoplastic disease and a shorter life expectancy than in the other group. The higher pre-stenting bilirubin value in the Ultraflex group is not consistent with this difference in age, as stated by the authors, because the bilirubin value does not indicate the spread of neoplasia, but can only reflect the mean period of bilirubin reduction after successful stenting [5].

Ahmad et al. report that the manufacturers have withdrawn the Ultraflex Diamond biliary stent from the United States market, although the reasons for this are not given. There are many possible reasons why manufacturers decide to suspend a product, often including economic factors. The Diamond biliary stent is still available in Europe, and the clinical results of a recent European multicenter study [6], as well as those from my personal unreported series of more than 60 Diamond stent placements, are very different from the results presented by Ahmad et al.

The occlusion rate, the patency period, and the survival period may be dependent on many stent-related or stenosis-related factors [7]. The relationship between stent-related and stenosis-related factors needs to be understood, since only this knowledge will allow selection of the ideal stent for any given stenosis, as well as the stent that is likely to lead to a better outcome in an individual patient [5]. At present, this decision mainly depends on the individual endoscopist’s experience with a particular type of stent, and on the local equipment. The availability of more types of metal biliary stents with different radial forces, materials, mesh designs, tissue reactions, etc., may help us to extend our expertise in selecting suitable stents and to improve the outcome of metal biliary stenting procedures in relation to stenosis-related factors, such as histology, length of the stricture, morphology, grade of the stricture, tumor tissue, etc. The question of which type of metal biliary stent needs to be placed in clinical practice during ERCP in any specific neoplastic biliary stricture, in order to achieve the best possible outcome, is still an open one.

References

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• 2 Ahmad J, Siqueira E, Martin J, Slivka A. Effectiveness of the Ultraflex Diamond stent for the palliation of malignant biliary obstruction.  Endoscopy. 2002;  34 793-796
• 3 Menon K, Romagnuolo J, Barkun A N. Expandable metal biliary stenting in patients with recurrent premature polyethylene stent occlusion.  Am J Gastroenterol. 2001;  96 1435-1440
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