Endoscopic papillectomy of benign ampullary lesions: Outcomes from a multicenter study

The Significance of Histopathological Findings on Clinical Outcomes in Endoscopic Papillectomy with Endocut

This study aimed to evaluate primary clinical outcomes in patients who underwent endoscopic papillectomy (EP) using the Endocut mode while examining the pathological characteristics of the margin of the resected specimen. To this end, 70 patients who underwent Endocut EP were included. Resection margins were classified according to pathological findings as "negative", "positive", or "uncertain (difficult pathological evaluation)". The effect of pathological resection margins on residual tumor recurrence rates was evaluated. The median follow-up was 47 months (range, 22-84). Eleven patients (15.7%) were diagnosed with residual tumors, ten of whom were diagnosed within 6 months after EP. The resection margins were pathologically negative in 27 patients, positive in 15, and uncertain in 28; residual tumors occurred in 5 patients (33.3%) in the positive group, 5 (17.9%) in the uncertain group, and 1 (3.7%) in the negative group. The patient in the negative group had familial adenomatous polyposis (FAP). Female sex, FAP, and uncertain or positive resection margins were significantly more common in residual patients (p = 0.009, 0.044, and 0.041, respectively). Pathological resection margins can be used to infer the residual tumor incidence, leading to early post-treatment of residual tumors.

Long-term recurrence after endoscopic versus surgical ampullectomy of sporadic ampullary adenomas: a systematic review and meta-analysis

BACKGROUND AND AIMS

Ampullary adenomas are treated both surgically and endoscopically, however, data comparing both techniques are lacking. We aimed to compare long-term recurrence of benign sporadic adenomas after endoscopic (EA) and surgical ampullectomy (SA).

METHODS

A comprehensive literature search of multiple databases (until December 29, 2020) was performed to identify studies reporting outcomes of EA or SA of benign sporadic ampullary adenomas. The outcome was recurrence rate at 1 year, 2-year, 3 year and 5 years after EA and SA.

RESULTS

A total of 39 studies with 1753 patients (1468 EA [age 61.1 ± 4.0 years, size 16.1 ± 4.0 mm], 285 SA [mean age 61.6 ± 4.48 years, size 22.7 ± 5.4 mm]) were included in the analysis. At year 1, pooled recurrence rate of EA was 13.0% (95% confidence interval [CI] 10.5-15.9], I² = 31%) as compared to SA 14.1% (95% CI 9.5-20.3 I² = 15.8%) (p = 0.82). Two (12.5%, [95% CI, 8.9-17.2] vs. 14.3 [95% CI, 9.1-21.6], p = 0.63), three (13.3%, [95% CI, 7.3-21.6] vs. 12.9 [95% CI, 7.3-21.6], p = 0.94) and 5 years (15.7%, [95% CI, 7.8-29.1] vs. 17.6% [95% CI, 6.2-40.8], p = 0.85) recurrence rate were comparable after EA and SA. On meta-regression, age, size of lesion or enbloc and complete resection were not significant predictors of recurrence.

CONCLUSION

EA and SA of sporadic adenomas have similar recurrence rates at 1, 2, 3 and 5 years of follow up.

Clinical practice guidelines for endoscopic papillectomy

The Japan Gastroenterological Endoscopy Society has developed the "Clinical Practice Guidelines for Endoscopic Papillectomy (EP)" as a fundamental guideline using scientific approach. EP is a recently spreading therapeutic modality for ampullary tumors ranked as high risk endoscopic technique. Because of the paucity of high level of evidence, strength of recommendations had to be determined by a consensus among specialists. These guidelines, shed light on the following five issues: Indications, Preoperative/intraoperative preparations and techniques, Early adverse events, Therapeutic outcomes and remnants/recurrences, and Follow-up and late adverse events, to guide current clinical practice on EP.

LONG-TERM FOLLOW-UP OF PATIENTS UNDERGOING ENDOSCOPIC PAPILLECTOMY FOR PAPILLARY NEUROENDOCRINE TUMOR: A CASE SERIES AND LITERATURE REVIEW

BACKGROUND

Duodenal papilla neuroendocrine tumors (DP-NET) are rare. Surgical therapy may be recommended for their treatment. However, they have high rates of morbidity and mortality. Endoscopic papillectomy (EP) is safe and effective for complete resection of tumors at this site.

OBJECTIVE

This study aimed to describe a case series of DP-NETs resected by EP and perform a literature review.

METHODS

A series of patients with DP-NETs underwent EP as primary treatment between Jan/2008 and Mar/2020 at a tertiary referral center. A comprehensive search was made on the MEDLINE primary electronic database. The search strategy was designed to find all articles related to DP-NETs published in the literature.

RESULTS

Six patients underwent EP for presenting DP-NETs, four of whom were women (mean age, 63 years). The mean diameter of DP-NETs was 1.6±0.3 cm. Four of six patients were followed up, one of whom suffered relapse at the resection site after 3 months and was referred to surgery (pT3n1b) and the remaining three patients experienced no endoscopic or histological recurrence during follow-up periods of 10, 7, and 4 years, respectively. Eighteen articles were found in the literature search in MEDLINE. The articles included case reports of endoscopically treated DP-NETs.

CONCLUSION

EP is safe and effective for DP-NETs that are ≤20 mm, confined to the submucosal layer, well-differentiated, and without local or remote metastasis. Adequate endoscopic follow-up and definitive surgical treatment in the presence of relapse are necessary.

Therapeutic Outcomes and Risk Factors for Complications of Endoscopic Papillectomy: A Retrospective Analysis of a Single-Center Study

Purpose

Endoscopic papillectomy (EP) has been accepted as a viable alternative therapy to surgery in benign duodenal papillary lesions. However, postoperative complications limit its widespread clinical application. This study aimed to evaluate the overall safety of the EP procedure and identify significant risk factors of post-EP complications.

Patients and Methods

We retrospectively collected 76 patients who had undergone EP in Chinese PLA General Hospital from 2016 to 2019 and graded their postoperative complications. We assessed twelve patient-, disease- or procedure-related variables to identify risk factors related to the occurrence of post-EP complications using both univariate and multivariate analyses.

Results

Among the 76 patients included in this study, the incidence of entire post-EP complications was 36.8%, most of which were in a mild form. In both univariate and multivariate analyses, the pathologic tumor types, especially high-grade intraepithelial neoplasia (HIN), and the placement of stents were significantly associated with the occurrence of post-EP complications. Patients with HIN tumors were more likely to have post-EP pancreatitis, bleeding, and overall complications (odds ratio (OR) 11.66, 95% confidence interval (CI) 2.91–62.5, P = 0.001; OR 6.52, 95% CI 1.45–46.77, P = 0.027; OR 9.81, 95% CI 2.75–44.04, P = 0.001, respectively). Pancreatic stent placement may contribute to the occurrence of post-EP pancreatitis (OR 7.61, 95% CI 1.37–64.53, P = 0.033). While biliary stent placement was found negatively related to the occurrence of post-EP bleeding and overall complications (OR 0.02, 95% CI 0–0.37, P = 0.016; OR 0.11, 95% CI 0.01–0.99, P = 0.05, respectively).

Conclusion

EP is a safe procedure for papillary lesion treatment with a low rate and generally mild postoperative complications. Two factors are significantly associated with the occurrence of complications. The selection of eligible patients and suitable procedures is important to reduce the complication rate and severity.

Endoscopic Ampullectomy of Benign Ampullary Lesions: Outcomes From a Single Center Study

BACKGROUND

Endoscopic ampullectomy (EA) offers an insignificantly intrusive strategy for viably treating mucosal and occasionally submucosal lesions of the ampulla of Vater and encompassing periampullary area with high achievement and is more secure. The aim of this study was to present safety, efficacy, and outcomes of EA in the treatment of benign lesions of ampulla Vater performed by single experienced endoscopists in a high volume center.

METHODS

This retrospective study was conducted in patients referred to our hospital (Turkey High Speciality Training and Research Hospital, Turkey) for endoscopic evaluation of ampullary benign lesions over an 8-year period (between October 2011 and September 2019). Success rate was defined as complete resection of lesions.

RESULTS

Twenty-nine patients with a median age of 64 years were included. Twenty-five patients had lesions confined to the ampulla vateri (86.2%). Accordingly, 2 lesions had intraductal extension adenoma (IDA) (6.9%) and 2 were lateral spreading adenoma (6.9%). The median size of the lesion was 17.5 mm (10 to 36 mm). Nineteen lesions (65.5%) were resected en bloc and 10 lesions (34.5%) were resected in piecemeal manner. Complete resection was achieved in 21 of 23 patients with benign ampullary lesions. The procedure success rate was 91.3%. Complications occurred in 6 patients (20.6%) of these 3 had (10.3%) bleeding, 2 (6.8%) had pancreatitis, and 1 had (3.4%) perforation. Four patients (13.7%) had a recurrence.

CONCLUSIONS

Deep resection of the benign ampullary lesions increases the complete resection rate, cannulation rate of the pancreatic duct, and stenting rate of the pancreatic duct. EA is a safe and successful procedure in patients with benign lesions of ampulla vater.

Endoscopic management of ampullary tumors: European Society of Gastrointestinal Endoscopy (ESGE) Guideline

1: ESGE recommends against diagnostic/therapeutic papillectomy when adenoma is not proven.Strong recommendation, low quality evidence. 2: ESGE recommends endoscopic ultrasound and abdominal magnetic resonance cholangiopancreatography (MRCP) for staging of ampullary tumors.Strong recommendation, low quality evidence. 3: ESGE recommends endoscopic papillectomy in patients with ampullary adenoma without intraductal extension, because of good results regarding outcome (technical and clinical success, morbidity, and recurrence).Strong recommendation, moderate quality evidence. 4: ESGE recommends en bloc resection of ampullary adenomas up to 20-30 mm in diameter to achieve R0 resection, for optimizing the complete resection rate, providing optimal histopathology, and reduction of the recurrence rate after endoscopic papillectomy.Strong recommendation, low quality evidence. 5: ESGE suggests considering surgical treatment of ampullary adenomas when endoscopic resection is not feasible for technical reasons (e. g. diverticulum, size > 4 cm), and in the case of intraductal involvement (of > 20 mm). Surveillance thereafter is still mandatory.Weak recommendation, low quality evidence. 6: ESGE recommends direct snare resection without submucosal injection for endoscopic papillectomy.Strong recommendation, moderate quality evidence. 7: ESGE recommends prophylactic pancreatic duct stenting to reduce the risk of pancreatitis after endoscopic papillectomy.Strong recommendation, moderate quality evidence. 8: ESGE recommends long-term monitoring of patients after endoscopic papillectomy or surgical ampullectomy, based on duodenoscopy with biopsies of the scar and of any abnormal area, within the first 3 months, at 6 and 12 months, and thereafter yearly for at least 5 years.Strong recommendation, low quality evidence.

十二指肠乳头息肉良、恶性病变比较及活检准确性

OBJECTIVE

To distinguish the endoscopic and clinical features of ampullary polyps, to investigate the endoscopic cancer risk factors of ampullary polyps based on the compared differences of benign lesions and adenocarcinoma, and to assess the accuracy of forceps biopsy.

METHODS

Authors retrospectively analyzed the data extracted from patients treated with endoscopic papillectomy (EP) from January 2009 to May 2019 in the Department of Gastroenterology, Peking University Third Hospital. Endoscopic pictures and pathology reports were reevaluated and analyzed. Differences between benign and cancer groups were conducted.

RESULTS

In the study, 42 cases were involved, 35 to 83 years old, containing 83.3% older than 50 years old patients. The histological types were as follows, 2 for inflammatory polyps (4.8%), 1 for neuroendocrine tumor (2.4%), 1 for hyperplastic polyp (2.4%), 5 for grade Ⅰ adenoma (11.9%), 10 for grade Ⅱ adenoma (23.8%), 4 for grade Ⅲ adenoma (9.5%) and 19 for adenocarcinoma (45.2%), and 90.5% were adenoma or adenocarcinoma. The average age of benign group (inflammatory polyps and adenomas) was (56.7±9.2), which was significantly younger than that of adenocarcinoma group [(66.0±9.8), P=0.004]. Tumor diameter in adenocarcinoma group[(2.3±0.8) cm] was significantly larger than that in benign group[(1.6±0.6) cm, P=0.002]. Benign lesions only showed Yamada type Ⅰ(57.1%)and type Ⅱ(42.9%). The percentage of Yamada type Ⅰ (36.8%)and type Ⅱ(31.6%) in adenocarcinoma group was lower than that in benign group. Moreover, Yamada type Ⅲ (31.5%) was only found in the adenocarcinoma group. Significant differences were observed between the two groups in Yamada types (P=0.046). Most of the benign lesions had clear boundary(18/21, 85.7%). The percentage of clear boundary in adenocarcinoma group (2/19, 10.5%) was significantly lower than that in the benign group (P < 0.001). No significant differences were investigated in color (P=0.353) and surface (P=0.324) between benign and adenocarcinoma lesions. Pooling age, lesion diameter, Yamada type and clear boundary into Logistic regression analysis, only age (OR=1.186, 95%CI 1.025-1.373, P=0.022) and clear boundary (OR=66.218, 95%CI 3.421-1 281.840, P=0.006) were the independent cancer risk factors. Only 2 (10.5%) in the 19 cancer patients had positive biopsy results before EP. As compared with post-EP, 55.3% (21/38) biopsies were under-estimated, including 17 (17/19, 89.5%) adenocarcinomas and 4 (4/10, 40%) grade Ⅱ adenomas.

CONCLUSION

adenoma and adenocarcinoma were the major histological type of ampullary po-lyps. Age and unclear boundary were the independent risk factors of ampullary adenocarcinoma. Forceps biopsy was not enough for ampullary polyp differentiation.

Anticoagulation and antiplatelet management in gastrointestinal endoscopy: A review of current evidence

The role of endoscopic procedures, in both diagnostic and therapeutic purposes is continually expanding and evolving rapidly. In this context, endoscopists will encounter patients prescribed on anticoagulant and antiplatelet medications frequently. This poses an increased risk of intraprocedural and delayed gastrointestinal bleeding. Thus, there is now greater importance on optimal pre, peri and post-operative management of anticoagulant and/or antiplatelet therapy to minimise the risk of post-procedural bleeding, without increasing the risk of a thromboembolic event as a consequence of therapy interruption. Currently, there are position statements and guidelines from the major gastroenterology societies. These are available to assist endoscopists with an evidenced-based systematic approach to anticoagulant and/or antiplatelet management in endoscopic procedures, to ensure optimal patient safety. However, since the publication of these guidelines, there is emerging evidence not previously considered in the recommendations that may warrant changes to our current clinical practices. Most notably and divergent from current position statements, is a growing concern regarding the use of heparin bridging therapy during warfarin cessation and its associated risk of increased bleeding, suggestive that this practice should be avoided. In addition, there is emerging evidence that anticoagulant and/or antiplatelet therapy may be safe to be continued in cold snare polypectomy for small polyps (< 10 mm).

Novel endoscopic papillectomy for reducing postoperative adverse events (with videos)

BACKGROUND

Pancreatic adenoma can potentially transform into adenocarcinoma, so it is recommended to be resected surgically or endoscopically. Endoscopic papillectomy is one of the main treatments for papillary adenoma, and bleeding, perforation, and pancreatitis are the most frequent and critical adverse events that restrict its wider use. There is no standard procedure for endoscopic papillectomy yet. The procedure is relevant to postoperative adverse events.

AIM

To reduce the postoperative adverse event rates and improve patients’ postoperative condition, we developed a standard novel procedure for endoscopic papillectomy.

METHODS

The novel endoscopic papillectomy had two main modifications based on the conventional method: The isolation of bile from pancreatic juice with a bile duct stent and wound surface protection with metal clips and fibrin glue. We performed a single-center retrospective comparison study on the novel and conventional methods to examine the feasibility of the novel method for reducing postoperative adverse events.

RESULTS

A total of 76 patients, of whom 23 underwent the novel procedure and 53 underwent the conventional procedure, were retrospectively evaluated in this study. The postoperative bleeding and pancreatitis rates of the novel method were significantly lower than those of the conventional method (0 vs 20.75%, P = 0.028, and 17.4% vs 41.5%, P = 0.042, respectively). After applying the novel method, the most critical adverse event, perforation, was entirely prevented, compared to a prevalence of 5.66% with the conventional method. Several postoperative symptoms, including fever, rapid pulse, and decrease in hemoglobin level, were significantly less frequent in the novel group (P = 0.042, 0.049, and 0.014, respectively). Overall, the total adverse event rate of the novel method was lower (0 vs 24.5%, P = 0.007) than that of the conventional method.

CONCLUSION

Patients who underwent the novel procedure had lower postoperative adverse event rates. This study demonstrates the potential efficacy and safety of the novel endoscopic papillectomy in reducing postoperative adverse events.

Best techniques for endoscopic ampullectomy

PURPOSE OF REVIEW

Endoscopic ampullectomy has proven its safety and efficacy in multiple studies, making it the favorable option for the management of endoscopic ampullectomy. In this review, we plan to review the basic steps every endoscopist should be familiar with before undertaking endoscopic ampullectomy.

RECENT FINDINGS

In this review, we plan to discuss the indications, preresection evaluation process including endoscopic ultrasound, endoscopic ampullectomy techniques with side-viewing endoscope and endoscopist experience/comfort with the management of the endoscopic ampullectomy complications.

SUMMARY

Things of utmost interest include reviewing all the ampullary biopsy specimens by an expert gastrointestinal pathologist, careful preresection staging, en bloc resection, familiarity with tools and techniques of endoscopic ampullectomy, postresection adverse events & management and postprocedure surveillance.

Endoscopic papillectomy for an ampullary neuroendocrine tumor

Ampullary neuroendocrine tumors (NETs) are extremely rare, have a high rate of transmural invasion and lymph node metastasis, and are generally recommended for surgery. In contrast, endoscopic papillectomy (EP) for ampullary NET, a low-grade type within the submucosal layer, is feasible and useful to avoid surgery. However, EP for ampullary NET is controversial, there are no consensus guidelines, and international recommendations are lacking. We present the case of a 60-year-old man with an ampullary NET who was successfully treated with EP via a hexagonal snare. Prior to EP, endoscopic ultrasonography, magnetic resonance cholangiopancreatography, and intraductal ultrasonography in endoscopic retrograde cholangiopancreatography were performed to assess for ductal infiltration of the NET. The specimen revealed a low-grade NET measuring 1.0 × 0.8 × 0.7 cm without venous or lymphatic infiltration, which was negative for horizontal and vertical margins. No recurrence was observed over a 12-month follow-up.

A Comprehensive Approach to the Management of Benign and Malignant Ampullary Lesions: Management in Hereditary and Sporadic Settings

PURPOSE OF REVIEW

The purpose of this review was to examine the historical roots of endoscopic management of ampullary lesions and explore emerging data on improved techniques, technologies, and outcomes. Of specific interest was answering whether there exists a reasonable body of data to support one resection technique or strategy above others.

RECENT FINDINGS

Review of recent literature suggests the continued use of endoscopic ampullectomy is a safe and effective means of curative treatment of ampullary adenomas. Complications are relatively infrequent and complete endoscopic resection is possible in a majority of cases, with proper patient and lesion selection. Greater than 2 decades of experience with endoscopic ampullectomy have shown this to be a viable, well-tolerated, and highly effective means of treating ampullary adenomas. While few concrete guidelines exist to advise endoscopists on the ideal technique for resection, experience, patient selection, and prior planning can greatly influence the technical and clinical success of endoscopic ampullectomy.

Insights and updates on endoscopic papillectomy

INTRODUCTION

Endoscopic papillectomy (EP) has been established as a useful endoscopic therapy by the efforts of many pancreatobiliary endoscopists and is presently accepted as a reliable alternative therapy to surgery in patients with ampullary adenoma. Moreover, there have been numerous advancements in EP techniques in recent years. Various approaches and attempts toward expanding the indications of endoscopic resection have been reported. Furthermore, the management and prevention of adverse events (AEs) and endoscopic treatment for remnant or recurrent lesions have also been reported. In the present review, we focus on recent advancements in the EP technique, as well as speculate on the future issues of EP.

AREA COVERED

This review of EP encompasses the indications, preoperative assessments, endoscopic techniques, outcomes, and AEs of EP, post-EP surveillance techniques, and treatments for remnant or recurrence lesions.

EXPERT OPINION

The ultimate goal of EP is the complete resection of ampullary tumors, regardless of whether they are adenomatous or carcinomatous lesions, without causing any AEs. Therefore, the most important issue is preoperative evaluation, that is, the accurate diagnosis of lesions contraindicated for EP. In addition, further research on the prevention of AEs is also necessary towards establishing EP as a safe endoscopic procedure.

Diagnosis, risk stratification, and management of ampullary dysplasia by DNA flow cytometric analysis of paraffin-embedded tissue

The limited accuracy of endoscopic biopsy in detecting high-grade dysplasia or adenocarcinoma within ampullary adenoma or dysplasia has been reported. The natural history of ampullary dysplasia is also unclear, and there are no established guidelines to determine which patients with ampullary dysplasia require resection versus surveillance endoscopy. DNA flow cytometry was performed on 47 ampullary biopsies with low-grade dysplasia, 18 high-grade dysplasia, and 23 negative for dysplasia, as well as 11 cases of ampullary adenocarcinoma. Abnormal DNA content (aneuploidy or elevated 4N fraction > 6%) was identified in 9 (82%) of adenocarcinoma, 13 (72%) of high-grade dysplasia, 7 (15%) of low-grade dysplasia, and none (0%) of non-dysplastic mucosa. One-, 2-, and 7-year detection rates of high-grade dysplasia or adenocarcinoma in low-grade dysplasia patients with abnormal DNA content were 57%, 86%, and 88%, respectively, whereas low-grade dysplasia patients in the setting of normal DNA content had 1-, 2-, and 7-year detection rates of 10%, 10%, and 10%, respectively. The univariate and multivariate hazard ratios (HRs) for subsequent detection of high-grade dysplasia or adenocarcinoma in low-grade dysplasia patients with DNA content abnormality were 16.8 (p = <0.01) and 9.8 (p = <0.01), respectively. Among the 13 high-grade dysplasia patients with DNA content abnormality, 5 patients (38%) were subsequently found to have adenocarcinoma within a mean follow-up time of 3 months, whereas only 1 (20%) of the remaining 5 patients in the setting of normal DNA content developed adenocarcinoma in a month (HR = 2.6, p = 0.39). The overall 1- and 2-year detection rates of adenocarcinoma in all high-grade dysplasia patients (regardless of flow cytometric results) were 34% (95% confidence interval = 16-63%) and 47% (95% confidence interval = 23-79%), respectively. In conclusion, the majority of low-grade dysplasia patients (86%) in the setting of abnormal DNA content developed high-grade dysplasia or adenocarcinoma within 2 years and thus may benefit from resection, whereas those with normal DNA content may be followed with surveillance endoscopy. The presence of DNA content abnormality can also confirm a morphologic suspicion of high-grade dysplasia, which should be managed with resection, as nearly 50% of the high-grade dysplasia patients were found to have adenocarcinoma within 2 years.

The efficacy of prophylactic pancreatic stents against complications of post-endoscopic papillectomy or endoscopic ampullectomy: a systematic review and meta-analysis

BACKGROUND

Endoscopic resection has been increasingly adopted for neoplasms in the major duodenal papilla. Previous studies have reached varying conclusions on whether prophylactic pancreatic stent (PS) placement is an effective measure against post-procedure complications. We aimed to investigate whether PS could reduce the incidence of post-procedure complications.

METHODS

The PubMed, Cochrane Library, and EMBASE databases were systematically searched from the inception dates to 25 December 2018 to identify all randomized controlled trials (RCTs) and retrospective cohort studies (RCSs) comparing prophylactic PS and no PS against post-procedure complications. The main outcomes measurements were post-procedure pancreatitis, bleeding, perforation and late papillary stenosis.

RESULTS

23 RCSs (1001 subjects) and 2 RCTs met the inclusion criteria. Meta-analysis of the RCSs showed that prophylactic PS decreased the odds of post-procedure pancreatitis (OR, 0.71; 95% CI, 0.36-1.40; p = 0.325) as well as late papillary stenosis (OR, 0.35; 95% CI, 0.07-1.75; p = 0.200; I ² =0%) and increased the odds of bleeding (OR, 1.32; 95% CI, 0.50-3.46; p = 0.572; I ² = 0%) and perforation (OR, 2.25; 95% CI, 0.33-15.50; p = 0.412; I ² = 0%) but not significantly. Sensitivity analysis illustrated prophylactic PS significantly decreased the risk of post-procedure pancreatitis (OR, 0.44; 95% CI, 0.24-0.80; p = 0.007).

CONCLUSIONS

PS placement was prophylactic against post-procedure complications although not significantly. Sensitivity analysis suggests the significant effect of prophylactic PS against post-procedure pancreatitis. More RCTs are required to validate the statistical significance of our results and potentially relevant characteristics improving the prophylactic efficacy of stents.