Comparison Between Novel Flower-type Covered Stent and Conventional Covered Stent

Covered self-expandable metal stent (C-CSEMS) has the risk of obstruction of the cystic duct, and the main and branch pancreatic ducts due to strong radial force and covering material, which results in cholecystitis and pancreatitis.

A flower-type covered self-expandable metal stent (F-CSEMS) having a five-petal-shaped design with side grooves was constructed to prevent the obstruction of the cystic duct orifice.

This study investigated the value of the F-CSEMS in protection for cholecystitis and pancreatitis.

The investigators will enroll patients with distal MBO (Malignant Biliary Obstruction) who received placement at the Samsung Medical Center. Transpapillary flower-type covered self-expandable metal stent (F-CSEMS) placements will be included in this study.

The diagnosis of MBO will be based on imaging and/or pathological findings. Malignancy was proved by histopathological confirmation obtained by endoscopic ultrasonography-guided fine-needle aspiration (EUS-FNA), bile duct biopsy (cytology), pancreatic duct cytology, or liver biopsy.

The investigators will evaluate the frequency of pancreatitis and cholecystitis.

Furthermore, the investigators will evaluate various parameters to clarify the predictive factors of pancreatitis and cholecystitis. The following 10 variables will be evaluated in pancreatitis by univariate analysis: [1] sex, [2] age, [3] primary disease, [4] Covered type (partially or fully), [5] SEMS with high AF, [6] F-CSEMS with high RF, [7] EST before F-CSEMS, [8] previous biliary stent, [9] contrast injection into the pancreatic duct (pancreatogram), and [10] the position of the distal stent edge.

The following 11 variables will be evaluated in cholecystitis by univariate analysis: [1] sex, [2] age, [3] regions of stricture, [4] F-CSEMS with high AF AF (axial force), [5] F-CSEMS with high RF, [6] previous biliary stent, [7] gallbladder stone, [8] contrast injection into the gallbladder (GB injection), [9] involvement to the orifice of the cystic duct (OCD), [10] position of distal stent edge, and [11] cystic duct occlusion by F-CSEMS.

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software: nQuery + nTerim (version 4.0)

• One-sided Chi-square test for proportion comparison

H0: p1=p2 vs H1: p1>p2 (The incidence of complications in the flower-type covered stent is smaller than in the conventional stent.)

p1 = incident rate of complication in full covered stent group p2 = incident rate of complication in flower-type covered stent group

• Set p1(incident rate of complication in full covered stent group) = 15% = 0.15
• expected % decrement in incidence rate = 40%, 50%, 60%, 70% --> p2 = 0.09, 0.075, 0.06, 0.045
• Significance level (alpha) = 0.05
• Maximum number of patients who can be enrolled = 10 per month at SMC = 120 per year
• Expected enroll period = 1 year = 12 months

1. Sample size calculation with targeted power of 80% Expected % decrement in incidence rate 70% p2 4.5% Required n per group 116 Required total sample size 232 Required enroll period (year) 1.9
2. Power calculation with a total sample size of 232 (116 per group) Expected % decrement in incidence rate 40% 50% 60% 70% p2 9.0% 7.5% 6.0% 4.5% Expected power (%) 32 48 64 80
3. Minimum % decrement to be detected with power of 80% Planned enroll period (year) 1 1.5 2 2.5 3 Enroll-able n per group 60 90 120 150 180 Enroll-able total sample size 120 180 240 300 360 Minimum % decrement to be detected 93.33% 78.70% 68.70% 62.70% 58.00% Expected p2 1.0% 3.2% 4.7% 5.6% 6.3%