A pilot study of a novel tapered and flared fully covered self-expandable metal stent for unresectable malignant distal biliary obstruction: a multicenter study in Japan

Toji Murabayashi; Makoto Kobayashi; Keisuke Iwata; Yuhei Iwasa; Yujiro Kawakami; Yoshiharu Masaki; Shinya Kawaguchi; Hayato Nakagawa

doi:10.5946/ce.2025.399

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Original Article A pilot study of a novel tapered and flared fully covered self-expandable metal stent for unresectable malignant distal biliary obstruction: a multicenter study in Japan: Toji Murabayashi^1,2, Makoto Kobayashi³, Keisuke Iwata⁴, Yuhei Iwasa⁴, Yujiro Kawakami⁵, Yoshiharu Masaki⁵, Shinya Kawaguchi⁶, Hayato Nakagawa²; Clinical Endoscopy 2026;59(3):425-432.
DOI: https://doi.org/10.5946/ce.2025.399
Published online: April 23, 2026

¹Department of Gastroenterology, Ise Red Cross Hospital, Ise, Japan

²Department of Gastroenterology and Hepatology, Mie University Graduate School of Medicine, Tsu, Japan

³Department of Gastroenterology, Yokkaichi Municipal Hospital, Yokkaichi, Japan

⁴Department of Gastroenterology, Gifu Municipal Hospital, Gifu, Japan

⁵Division of Gastroenterology and Hepatology, Department of Internal Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan

⁶Department of Gastroenterology, Shizuoka General Hospital, Shizuoka, Japan

Correspondence: Toji Murabayashi Department of Gastroenterology, Ise Red Cross Hospital, 1-471-2, Funae, Ise, Mie, 516-8512, Japan E-mail: murabayashitoji@m2.gmobb.jp

• Received: October 25, 2025 • Revised: December 19, 2025 • Accepted: December 30, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Abstract
Graphical abstract
INTRODUCTION
METHODS
RESULTS
DISCUSSION
NOTES
REFERENCES

See letter "Beyond cylindrical stents: does a tapered-and-flared design improve biliary drainage?" in Volume 59 on page 406.

Abstract

Background/Aims
This study evaluated the feasibility and clinical outcomes of a novel tapered and flared, fully covered, self-expandable metal stent (TF-FCSEMS) for unresectable malignant distal biliary obstruction (UMDBO).
Methods
This multicenter retrospective study included 40 patients who underwent transpapillary placement of a TF-FCSEMS (10-mm cylindrical body with an 8-mm tapered distal end) for UMDBO between May 2023 and July 2024. The primary outcome was time to recurrent biliary obstruction (TRBO). Secondary outcomes included technical and clinical successes, adverse events (AEs), and overall survival.
Results
Technical and clinical success rates were 100% and 98%, respectively. During a median follow-up period of 271 days, recurrent biliary obstruction (RBO) occurred in 10 (26%) of the 39 patients who achieved clinical success. The median TRBO was 539 days (95% confidence interval, 389–not reached), and the non-RBO rates at 3, 6, and 12 months were 94%, 71%, and 61%, respectively. Symptomatic stent migration occurred in 2 patients (5.1%), while asymptomatic migration was observed in 3 (7.7%). Post-endoscopic retrograde cholangiopancreatography pancreatitis occurred in four patients (10%). Non-occlusion cholangitis developed in five (13%) patients, mostly with tumor-related duodenal stenosis. All AEs were managed conservatively or endoscopically.
Conclusions
TF-FCSEMS appears to be a feasible and acceptable treatment option for UMDBO. Further prospective studies are required to confirm these findings.
Keywords: Bile duct neoplasms; Drainage; Pancreatic neoplasms; Stents

Graphical abstract

INTRODUCTION

Endoscopic transpapillary biliary drainage using fully covered self-expandable metal stents (FCSEMS) is the most common treatment for malignant distal biliary obstruction (MDBO).¹^,² However, recurrent biliary obstruction (RBO) remains a major clinical issue after successful FCSEMS placement. The two most frequent causes of RBO in patients with MDBO treated with FCSEMS are stent migration and stent occlusion due to biliary debris.²^-⁴

A tapered and flared FCSEMS (TF-FCSEMS) has recently been developed. This device has a novel conceptual design, incorporating both a tapered segment and a flared distal end, intended to reduce the incidence of stent migration and occlusion.⁵ This study evaluated the effectiveness of transpapillary biliary drainage using a TF-FCSEMS in patients with MDBO.

METHODS

Study design

This multicenter retrospective observational study was conducted at five Japanese tertiary institutions: Ise Red Cross Hospital, Yokkaichi Municipal Hospital, Gifu Municipal Hospital, Sapporo Medical University, and Shizuoka General Hospital. This study was approved by the institutional review boards of all participating institutions, and informed consent was obtained through opt-out forms posted on their respective websites. This study was registered with the University Hospital Medical Information Network Clinical Trials Registry of Japan (UMIN000057746). This study aimed to evaluate the effectiveness of the TF-FCSEMS in unresectable MDBO (UMDBO).

Patients

Patients who underwent transpapillary placement of a 10-mm diameter TF-FCSEMS for UMDBO at five participating centers between May 2023 and July 2024 were retrospectively and consecutively enrolled. The exclusion criteria were as follows: (1) patients with prior endoscopic or surgical bilioenteric anastomosis, such as hepaticogastrostomy; (2) patients with severe cirrhosis or extensive liver metastases that would hinder the evaluation of clinical success; (3) patients with a history of biliary drainage using TF-FCSEMSs; and (4) patients who underwent multiple biliary stent placement.

Novel tapered and flared fully covered self-expandable metal stent

The TF-FCSEMS used in this study was a newly developed FCSEMS featuring both a tapered segment and a flared end (K-papilla stent; S and G Biotech) (Fig. 1).⁵ The K-papilla stent is composed of a cross-and-hook-structured nitinol wire and a silicone membrane, which comprises three components: a cylindrical body, a 3-cm tapered section, and a 1-cm flared end located on the duodenal side. The tapered section was gradually narrowed toward the duodenal end, with the narrowest pointpositioned 1 cm from the distal edge and designed to be aligned with the biliary orifice of the papilla (Fig. 2). This tapered portion is subjected to oblique forces generated by both the malignant stricture and the physiological resistance at the papilla, resulting in a continuous upstream force acting on the stent. A large distal flare prevents proximal migration into the bile duct (Fig. 2). The K-papilla stent is available in two diameter options: one with a cylindrical body diameter of 10 mm and a narrowest point of 8 mm, and the other with a body diameter of 12 mm and a narrowest point of 10 mm. An 8.5F delivery system was used in both versions. In this study, only a stent with a 10-mm body and an 8-mm narrowest point was used. The K-papilla stent has been commercially available in Japan since May 2023 and was subsequently introduced in Korea.

Endoscopic procedures

TF-FCSEMS placement was performed using standard endoscopic retrograde cholangiopancreatography (ERCP) procedures under conscious sedation. Written informed consent was obtained from all participants for the endoscopic procedures. After confirming the presence of a distal biliary stricture using cholangiography, a TF-FCSEMS was deployed across the stricture and papilla to position the narrowest point of the stent at the level of the papilla. The stent length was selected based on cholangiographic findings. Endoscopic sphincterotomy (EST) was performed before stent insertion in all patients, except for those at high risk for EST, such as patients receiving antithrombotic therapy, those with tumor invasion of the papilla, and those with an intradiverticular papilla. Prophylactic pancreatic or gallbladder stents were placed at the discretion of the endoscopist. All patients were hospitalized for at least 24 hours after the procedure to monitor adverse events (AEs), including post-ERCP pancreatitis (PEP).

Outcome measurements and definitions

The primary outcome was time to RBO (TRBO). Secondary outcomes included the technical success rate, clinical success rate, AE rate, and survival period. Most outcome definitions were based on the Tokyo Criteria 2024.⁶ Technical success was defined as a successful stent placement at the intended location.⁶ Clinical success was defined as a ≥50% reduction in total bilirubin or complete normalization within 14 days in patients with jaundice; and as a sufficient reduction or normalization of targeted liver enzymes, or resolution of cholangitis within 14 days, in non-jaundiced patients.⁶ Because the Tokyo Criteria 2024 does not define clinical success in asymptomatic patients undergoing scheduled plastic stent exchange, it was independently defined as the absence of RBO for more than 14 days after stent exchange. RBO was defined as a composite endpoint, including stent occlusion or migration leading to RBO or other conditions requiring biliary drainage or stent removal.⁶ The causes of RBO were determined based on findings from endoscopic reintervention and/or abdominal imaging, according to the Tokyo Criteria 2024,⁶ and included stent occlusion (due to tumor ingrowth, reactive mucosal hyperplasia, overgrowth, biliary debris or stones, food impaction, hemobilia, or other causes), stent migration, kinking, other biliary events requiring drainage, and stent removal due to AEs possibly related to the stent. TRBO is defined as the time from stent placement to biliary drainage or stent removal for RBO.⁶ Cumulative non-RBO rates at 3, 6, and 12 months were assessed. The AEs were categorized as RBO, pancreatitis, cholecystitis, bleeding, perforation, liver abscess, non-occlusion cholangitis, and others. AEs were classified as early (occurring within 14 days) or late (occurring after 14 days). Cholecystitis was evaluated according to the Tokyo Guidelines 2018,⁷ and non-occlusion cholangitis was defined as cholangitis that could be managed conservatively without biliary drainage.⁶ Cholangitis was evaluated based on the Tokyo Guidelines 2018.⁸ Other AEs, including pancreatitis and bleeding, were assessed using the American Society for Gastrointestinal Endoscopy lexicon.⁹ Asymptomatic stent migration was evaluated in detail, including the timing of occurrence, symptom onset (if any), and endoscopic reintervention (if any). Migration identified incidentally on imaging without clinical symptoms was not considered as RBO. Cases in which stent replacement was performed solely because of asymptomatic migration were censored at the time of stent replacement in the TRBO analysis.

Statistical analysis

Continuous variables are presented as mean values with standard deviations, and categorical variables are reported as counts and percentages. Cumulative TRBO and survival during the follow-up period were analyzed using the Kaplan-Meier method. Univariate and multivariate analyses using the Cox proportional hazards model were performed to identify the candidate risk factors for RBO. Hazard ratios (HRs) and 95% confidence intervals (CIs) were also calculated. A p-value of <0.05 was considered statistically significant. All statistical analyses were performed using the EZR ver. 1.54 (Saitama Medical Center, Jichi Medical University).¹⁰

Ethical statements

The study was approved by the Institutional Review Board of the Ise Red Cross Hospital (approval number: ER2024-105). Informed consent was obtained through opt-out forms posted on websites. All the procedures were performed in accordance with the ethical standards of the 1964 Declaration of Helsinki and its later amendments.

RESULTS

Patients

Between May 2023 and July 2024, 42 patients who underwent transpapillary placement of a TF-FCSEMS with a 10-mm body for UMDBO were enrolled in this study. Two patients were excluded: one with a history of endoscopic ultrasound-guided hepaticogastrostomy (EUS-HGS) and the other with prior biliary drainage using a TF-FCSEMS. Forty patients (19 males) were included in the final analysis. The baseline characteristics of the patients are summarized in Table 1. The primary malignancies causing UMDBO were pancreatic cancer in 32 patients (80.0%), bile duct cancer in five (12.5%), and other cancers in three (7.5%). Histological confirmation was obtained through tissue acquisition in 37 patients (92.5%); in the remaining three patients (7.5%), the diagnosis was based on the clinical course and imaging findings during follow-up. The reasons for non-resection included metastatic disease in 20 patients (50.0%), locally advanced disease in nine patients (22.5%), and poor general condition and/or patient refusal in 11 patients (27.5%). Prior biliary drainage was performed in 27 patients (67.5%).

Short-term outcomes and characteristics of biliary drainage

Table 2 summarizes the characteristics of the biliary drainage and short-term outcomes. The technical success rate was 100%. The most commonly used stent length was 6 cm (53%). The biliary stricture was fully included within the tapered portion of the TF-FCSEMS in 24 patients (60.0%), partially included in seven (17.5%), and not included in nine (22.5%). Simultaneous pancreatic and gallbladder stenting was performed in four patients (10.0%) and three patients (7.5%), respectively. Of the three patients who underwent prophylactic gallbladder stenting, two had tumor invasion of the cystic duct, while one did not.

The clinical success rate was 97.5% (39/40 patients). A single case of clinical failure occurred due to tumor-related bleeding, which necessitated the replacement of the TF-FCSEMS with a 12-mm FCSEMS 8 days after the initial placement. Early AEs occurred in six patients (15.0%), including PEP in four, cholecystitis in one, and bleeding in one. All cases of PEP were classified as mild. In one of these cases, an additional pancreatic stent was placed 2 days after TF-FCSEMS placement. The cholecystitis was also mild and was successfully managed with percutaneous transhepatic gallbladder aspiration.

Long-term outcomes

After TF-FCSEMS placement, thirty-nine patients were followed up until death or April 2025. Chemotherapy or chemoradiotherapy was administered to 27 (67.5%) patients. During a median follow-up period of 271 days (range, 27–698 days), RBO occurred in 10 of the 39 patients who achieved clinical success (Table 3). The median cumulative TRBO was 539 days (95% CI, 389–not reached [NR]) (Fig. 3). The non-RBO rates at 3, 6, and 12 months were 94.3% (33/35), 71.4% (20/28), and 61.1% (11/18), respectively. The causes of RBO included stent occlusion due to biliary debris in six patients, overgrowth in two, and distal migration in two. In one patient, asymptomatic stent migration was detected on day 114, and RBO due to migration subsequently developed on day 288. This patient, who also had duodenal stenosis, was successfully treated with EUS-HGS. In this patient, temporary improvement in the biliary stricture was attributed to tumor shrinkage following chemotherapy. In another patient with stent migration, RBO occurred on day 80 and was likely related to marked bile duct tortuosity. No further biliary drainage was performed because the patient’s general condition deteriorated. Among the remaining eight patients with RBO, metal stent replacement was performed in seven, and EUS-HGS was performed in one patient with duodenal stenosis. Late AEs included non-occlusion cholangitis in five patients and liver abscess in one patient. All events were successfully managed with antibiotics alone without the need for additional drainage or ERCP. Non-occlusion cholangitis occurred at a median of 195 days (161, 169, 195, 204, and 263 days) after TF-FCSEMS placement. Among these five patients, four developed cholangitis in association with newly developed malignant duodenal stenosis due to tumor progression. Regarding the location of the stenosis,¹¹^,¹² three patients had Type II stenosis (involving the major papilla), and the remaining patient had Type III stenosis (distal to the major papilla). Endoscopic duodenal stent placement was subsequently performed in these four patients. Asymptomatic stent migration was observed in three patients on days 161, 350, and 492. Tumor shrinkage following chemoradiotherapy was considered a potential contributing factor in two of these cases. In the first and third cases, no RBO occurred more than 6 months after stent migration. In the second case, a plastic stent was placed the day after migration was detected.

Risk factors for RBO

According to univariate analyses of six factors using the Cox proportional hazards model, biliary stricture not within the tapered portion of the stent was the only significant risk factor for RBO (HR, 10.40; 95% CI, 2.24–48.60; p=0.003) (Table 4). Among the two factors with a p-value <0.1 in univariate analyses, biliary stricture not within the tapered portion of the stent was the only significant risk factor for RBO in multivariate analysis (HR, 7.96; 95% CI, 1.47–43.00; p=0.02) (Table 4).

DISCUSSION

To our knowledge, this is the first report to evaluate the effectiveness of the newly designed TF-FCSEMS. This pilot study demonstrated that the TF-FCSEMS is a feasible and acceptable treatment option for UMDBO. In this study, the median TRBO was remarkably long at 539 days (95% CI, 389–NR), and AE incidence following stent placement was relatively low. We speculate that these favorable outcomes may be attributable to the unique design of the TF-FCSEMS, which appears to reduce stent migration and biliary sludge formation.

Stent migration occurred in 12.8% of the patients (5/39), including two symptomatic and three asymptomatic cases, a rate slightly lower than those reported in previous studies using conventional FCSEMSs. Moreover, in two of these five cases, migration occurred more than 300 days after TF-FCSEMS placement. Of the five cases in which migration occurred, three showed marked tumor shrinkage following antitumor therapy (chemoradiotherapy in two and chemotherapy in one). In the remaining two cases, the patients received chemotherapy, but no tumor shrinkage was observed at the time of migration. Before conducting this study, however, we hypothesized that the migration rate with the TF-FCSEMS would be markedly low owing to its structural features. The tapered segment of the TF-FCSEMS generates a continuous upstream force that may help prevent distal migration, while the flared distal end may act as a physical anchor to resist the proximal migration caused by this force. In this study, a TF-FCSEMS with a cylindrical body diameter of 10 mm and a narrowest tapered point of 8 mm was used. Further modifications to produce a more pronounced taper, such as narrowing the distal point to 4 mm, may reduce the incidence of stent migration by increasing the upstream force acting on the stent.

Another potential advantage of the TF-FCSEMS is its ability to suppress biliary sludge formation through the pressure gradient generated by the tapered lumen. According to the principles of fluid dynamics, the flow is naturally directed from wider to narrower sections, which may enhance bile drainage and reduce sludge accumulation. Doi et al.¹³ reported a remarkably long median TRBO of 503 days using an FCSEMS with a 1.5-cm tapered end (from 8 to 6 mm) for UMDBO. They hypothesized that a favorable pressure gradient contributes to reduced stent occlusion due to biliary sludge. However, they also reported a relatively high migration rate of 22.8% (distal migration, 17.1%; proximal migration, 5.7%). The TF-FCSEMS used in the present study may offer an advantage over such devices by combining a tapered segment with a flared distal end, which may help mitigate the risk of migration.

In this study, PEP occurred in four patients (10.0%), a rate comparable to that reported in previous studies using FCSEMS for MDBO. The large distal flare of the TF-FCSEMS does not appear to adversely affect the pancreatic orifice; therefore, it may not increase the risk of PEP compared with the conventional FCSEMS. The TF-FCSEMS used in this study had the narrowest tapered point of 8 mm and was designed to be positioned in the papilla. This design aimed to reduce PEP incidence compared with a conventional FCSEMS with a uniform 10-mm diameter. However, a randomized controlled trial by Kawashima et al. found no significant difference in PEP rates between 8-mm and 10-mm FCSEMS in patients with UMDBO.¹⁴ These findings are consistent with our results and may explain why PEP incidence in our study was not significantly different. Similarly, modifying the stent to incorporate a more pronounced taper, such as narrowing the distal point to 4 mm, might further reduce PEP incidence by decreasing the mechanical stress on the pancreatic orifice.

In this study, non-occlusion cholangitis occurred in five patients (12.8%), a rate slightly higher than that reported in previous studies using FCSEMS for MDBO. The large distal flare of the TF-FCSEMS may have contributed to the development of non-occlusion cholangitis, as the duodenal fluid may be more prone to reflux into the bile duct than the conventional FCSEMS. However, no experimental or basic research supports this proposed mechanism. In most cases in this study, non-occlusion cholangitis appeared to be associated with malignant duodenal stenosis (type II or III¹¹^,¹²) due to tumor progression at onset. The longer TRBO observed with TF-FCSEMSs may have also contributed to the higher incidence of non-occlusion cholangitis by allowing more time for tumor progression than with conventional FCSEMS.

In this study, cholecystitis occurred in one patient (2.5%), a rate comparable to that reported in previous studies using FCSEMS for MDBO. Notably, three of the 40 patients had previously undergone cholecystectomy, and three cases underwent simultaneous gallbladder stenting using a plastic stent. Because tapered and flared sections of TF-FCSEMSs usually do not affect the cystic duct, the incidence of cholecystitis with TF-FCSEMSs may not differ significantly from that observed with conventional cylindrical FCSEMS. Indeed, because the TF-FCSEMS has no flare at the hepatic end, it may exert less impact on the cystic duct than conventional FCSEMS, some of which have a small flare at the hepatic end.

TF-FCSEMS has a 3-cm-long tapered portion; therefore, its clinical benefit may be reduced in cases with biliary strictures located >3 cm upstream of the papilla, as such strictures cannot be encompassed by the tapered portion of the stent. Interestingly, in this study, biliary strictures that were not within the tapered portion of the TF-FCSEMS were identified as significant risk factors for RBO (Table 4). Notably, this finding did not statistically correlate with the occurrence of stent migration. Because this finding corresponds to strictures situated >3 cm upstream of the papilla, the true risk factor might be the stricture location itself. In fact, RBO due to tumor overgrowth occurred in two of the nine cases in which the biliary stricture was not within the tapered portion of the TF-FCSEMS.

This study had several limitations, including its retrospective design, single-arm nature, and small sample size. Future randomized controlled trials are necessary to evaluate the potential superiority of TF-FCSEMSs over conventional cylindrical FCSEMS for MDBO. The present findings provide a preliminary foundation for future investigations.

In conclusion, the TF-FCSEMS appears to be a feasible and acceptable treatment option for UMDBO. Further modifications to the degree of tapering may improve the clinical outcomes. Continued research and development of TF-FCSEMSs are warranted.

Conflicts of Interest

The authors have no potential conflicts of interest.

Funding

None.

Author Contributions

Conceptualization: TM, MK; Data curation: TM; Formal analysis: TM; Investigation: TM, MK, YI, KI, YK, YM, SK; Methodology: TM; Project administration: TM; resources: TM, MK, YI, KI, YK, YM, SK; Supervision: HN, Validation: TM, Visualization: TM, Writing–original draft: TM; Writing–review & editing: TM.

Fig. 1.

A newly developed tapered and flared fully covered self-expandable metal stent (K-papilla stent; S and G Biotech). The stent consisted of three components: a cylindrical body, a 3-cm tapered section, and a 1-cm flared end located on the duodenal side. The tapered section gradually narrowed toward the distal (duodenal) end.

Fig. 2.

A case of successful stent placement using a tapered and flared fully covered self-expandable metal stent (TF-FCSEMS). (A) Fluoroscopic image of the TF-FCSEMS. (B) Endoscopic image of the TF-FCSEMS. The large distal flare is intended to prevent proximal migration into the bile duct.

Fig. 3.

Kaplan-Meier curve of time to recurrent biliary obstruction (TRBO). The median TRBO was 539 days (95% confidence interval, 389–not reached). Small vertical bars on the survival curve indicate censored observations.

Table 1.

Patient characteristics (n=40)

Characteristic	Value
Age (yr)	76 (52–93)
Sex, male/female	19 (47.5)/21 (52.5)
Cancer type
Pancreatic cancer	32 (80.0)
Bile duct cancer	5 (12.5)
Malignant lymphoma	2 (5.0)
Gastric cancer	1 (2.5)
Reason for non-resection
Metastatic disease	20 (50.0)
Locally advanced disease	9 (22.5)
Poor general condition and/or patient refusal	11 (27.5)
Performance status
0–2	33 (82.5)
3–4	7 (17.5)
Tumor invasion of the duodenum	12 (30.0)
Main pancreatic duct obstruction by tumor	26 (65.0)
Tumor involvement of the cystic duct
Present	11 (27.5)
Absent	26 (65.0)
Post-cholecystectomy	3 (7.5)
Serum total bilirubin level (mg/dL)	2.0 (0.3–24.8)
Prior biliary drainage
Plastic stent	16 (40.0)
Metal stent	10 (25.0)
PTBD	1 (2.5)
None	13 (32.5)
Antitumor therapy
Chemotherapy	24 (60.0)
Chemoradiotherapy	3 (7.5)
Best supportive care	13 (32.5)
Diameter of bile duct (mm)	11 (8–22)

Values are presented as median (range) or number (%).

PTBD, percutaneous transhepatic biliary drainage.

Table 2.

Short-term outcomes and characteristics of biliary drainage (n=40)

Characteristic	Value
Technical success	40 (100.0)
Clinical success	39 (97.5)
Stent length (TF-FCSEMS)
8 cm	16 (40.0)
7 cm	3 (7.5)
6 cm	21 (52.5)
Relationship between biliary stricture and tapered portion
Completely included within the tapered portion	24 (60.0)
Partially included within the tapered portion	7 (17.5)
Not included within the tapered portion	9 (22.5)
Simultaneous pancreatic stenting	4 (10.0)
Simultaneous gallbladder stenting	3 (7.5)
Early AEs	6 (15.0)
Pancreatitis	4 (10.0)
Cholecystitis	1 (2.5)
Bleeding	1 (2.5)

TF-FCSEMS, tapered and flared fully covered self-expandable metal stent; AE, adverse event.

Table 3.

Long-term outcomes (n=39)

Variable	Value
RBO (n, %)	10 (25.6)
Cause of RBO (n, %)
Stent occlusion due to biliary debris	6 (15.4)
Stent occlusion due to overgrowth	2 (5.1)
Distal migration	2 (5.1)
TRBO (median, 95% CI; day)	539 (389–NR)
Non-RBO rate at 3 months (%, n/total n)	94.3 (33/35)
Non-RBO rate at 6 months (%, n/total n)	71.4 (20/28)
Non-RBO rate at 12 months (%, n/total n)	61.1 (11/18)
Late AEs (excluding RBO) (n, %)
Non-occlusion cholangitis	5 (12.8)
Liver abscess	1 (2.6)
Migration (n, %)	5 (12.8)
Symptomatic migration	2 (5.1)
Asymptomatic migration	3 (7.7)
Follow-up duration (median, range; day)	271 (27–698)
Overall survival (median, 95% CI; day)	252 (173–NR)

RBO, recurrent biliary obstruction; TRBO, time to recurrent biliary obstruction; CI, confidence interval; NR, not reached; AE, adverse event.

Table 4.

Cox proportional hazards model analysis of risk factors for recurrent biliary obstruction

	Univariate analysis		Multivariate analysis
	HR (95% CI)	p-value	HR (95% CI)	p-value
Pancreatic cancer	2.96 (0.36–24.30)	0.31
Tumor invasion of duodenum	0.38 (0.05–3.13)	0.37
Prior drainage	0.27 (0.06–1.20)	0.09	0.54 (0.10–2.89)	0.47
Antitumor therapy	0.61 (0.17–2.16)	0.45
Diameter of bile duct	0.92 (0.73–1.12)	0.48
Stricture not within the stent’s tapered portion	10.40 (2.24–48.60)	0.003	7.96 (1.47–43.00)	0.02

HR, hazard ratio; CI, confidence interval.

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A pilot study of a novel tapered and flared fully covered self-expandable metal stent for unresectable malignant distal biliary obstruction: a multicenter study in Japan

Clin Endosc. 2026;59(3):425-432. Published online April 23, 2026

DOI: https://doi.org/10.5946/ce.2025.399

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A pilot study of a novel tapered and flared fully covered self-expandable metal stent for unresectable malignant distal biliary obstruction: a multicenter study in Japan

Fig. 1. A newly developed tapered and flared fully covered self-expandable metal stent (K-papilla stent; S and G Biotech). The stent consisted of three components: a cylindrical body, a 3-cm tapered section, and a 1-cm flared end located on the duodenal side. The tapered section gradually narrowed toward the distal (duodenal) end.

Fig. 2. A case of successful stent placement using a tapered and flared fully covered self-expandable metal stent (TF-FCSEMS). (A) Fluoroscopic image of the TF-FCSEMS. (B) Endoscopic image of the TF-FCSEMS. The large distal flare is intended to prevent proximal migration into the bile duct.

Fig. 3. Kaplan-Meier curve of time to recurrent biliary obstruction (TRBO). The median TRBO was 539 days (95% confidence interval, 389–not reached). Small vertical bars on the survival curve indicate censored observations.

Graphical abstract

Fig. 1.

Fig. 2.

Fig. 3.

Graphical abstract

A pilot study of a novel tapered and flared fully covered self-expandable metal stent for unresectable malignant distal biliary obstruction: a multicenter study in Japan

Characteristic	Value
Age (yr)	76 (52–93)
Sex, male/female	19 (47.5)/21 (52.5)
Cancer type
Pancreatic cancer	32 (80.0)
Bile duct cancer	5 (12.5)
Malignant lymphoma	2 (5.0)
Gastric cancer	1 (2.5)
Reason for non-resection
Metastatic disease	20 (50.0)
Locally advanced disease	9 (22.5)
Poor general condition and/or patient refusal	11 (27.5)
Performance status
0–2	33 (82.5)
3–4	7 (17.5)
Tumor invasion of the duodenum	12 (30.0)
Main pancreatic duct obstruction by tumor	26 (65.0)
Tumor involvement of the cystic duct
Present	11 (27.5)
Absent	26 (65.0)
Post-cholecystectomy	3 (7.5)
Serum total bilirubin level (mg/dL)	2.0 (0.3–24.8)
Prior biliary drainage
Plastic stent	16 (40.0)
Metal stent	10 (25.0)
PTBD	1 (2.5)
None	13 (32.5)
Antitumor therapy
Chemotherapy	24 (60.0)
Chemoradiotherapy	3 (7.5)
Best supportive care	13 (32.5)
Diameter of bile duct (mm)	11 (8–22)

Characteristic	Value
Technical success	40 (100.0)
Clinical success	39 (97.5)
Stent length (TF-FCSEMS)
8 cm	16 (40.0)
7 cm	3 (7.5)
6 cm	21 (52.5)
Relationship between biliary stricture and tapered portion
Completely included within the tapered portion	24 (60.0)
Partially included within the tapered portion	7 (17.5)
Not included within the tapered portion	9 (22.5)
Simultaneous pancreatic stenting	4 (10.0)
Simultaneous gallbladder stenting	3 (7.5)
Early AEs	6 (15.0)
Pancreatitis	4 (10.0)
Cholecystitis	1 (2.5)
Bleeding	1 (2.5)

Variable	Value
RBO (n, %)	10 (25.6)
Cause of RBO (n, %)
Stent occlusion due to biliary debris	6 (15.4)
Stent occlusion due to overgrowth	2 (5.1)
Distal migration	2 (5.1)
TRBO (median, 95% CI; day)	539 (389–NR)
Non-RBO rate at 3 months (%, n/total n)	94.3 (33/35)
Non-RBO rate at 6 months (%, n/total n)	71.4 (20/28)
Non-RBO rate at 12 months (%, n/total n)	61.1 (11/18)
Late AEs (excluding RBO) (n, %)
Non-occlusion cholangitis	5 (12.8)
Liver abscess	1 (2.6)
Migration (n, %)	5 (12.8)
Symptomatic migration	2 (5.1)
Asymptomatic migration	3 (7.7)
Follow-up duration (median, range; day)	271 (27–698)
Overall survival (median, 95% CI; day)	252 (173–NR)

	Univariate analysis		Multivariate analysis
	HR (95% CI)	p-value	HR (95% CI)	p-value
Pancreatic cancer	2.96 (0.36–24.30)	0.31
Tumor invasion of duodenum	0.38 (0.05–3.13)	0.37
Prior drainage	0.27 (0.06–1.20)	0.09	0.54 (0.10–2.89)	0.47
Antitumor therapy	0.61 (0.17–2.16)	0.45
Diameter of bile duct	0.92 (0.73–1.12)	0.48
Stricture not within the stent’s tapered portion	10.40 (2.24–48.60)	0.003	7.96 (1.47–43.00)	0.02

Table 1. Patient characteristics (n=40)

Values are presented as median (range) or number (%).

PTBD, percutaneous transhepatic biliary drainage.

Table 2. Short-term outcomes and characteristics of biliary drainage (n=40)

TF-FCSEMS, tapered and flared fully covered self-expandable metal stent; AE, adverse event.

Table 3. Long-term outcomes (n=39)

RBO, recurrent biliary obstruction; TRBO, time to recurrent biliary obstruction; CI, confidence interval; NR, not reached; AE, adverse event.

Table 4. Cox proportional hazards model analysis of risk factors for recurrent biliary obstruction