








































Key Words Competing Interests Article Information

Urethral stricture, dilatation,  
drug-coated balloon, paclitaxel,  
lower urinary tract symptoms

The study was sponsored and funded by 
Urotronic Inc.

Received on July 28, 2021 
Accepted on September 2, 2021 
This article has been peer reviewed.

Soc Int Urol J. 2022;3(1):21–27

DOI: 10.48083/MLXK5817

21SIUJ.ORG SIUJ  •  Volume 3, Number 1  •  January 2022

This is an open access article under the terms of a license that permits non-commercial use, provided the original work is properly cited.  
© 2022 The Authors. Société Internationale d'Urologie Journal, published by the Société Internationale d'Urologie, Canada.

ORIGINAL RESEARCH

One-Year Outcomes of the ROBUST II Study 
Evaluating the Use of a Drug-Coated Balloon  
for Treatment of Urethral Stricture
Jessica M. DeLong,1 Michael J. Ehlert,2 Bradley A. Erickson,3 Kaiser J. Robertson,4  
Ramón Virasoro,1 Sean P. Elliott5

1 Urology of Virginia, Virginia Beach, United States 2 Metro Urology, a Division of Minnesota Urology, Woodbury, United States 3 Department of Urology, University of 
Iowa, Iowa City, United States 4 Chesapeake Urology, Hanover, United States 5 Department of Urology, University of Minnesota, Minneapolis, United States

Abstract

Objectives To report 1-year results of the ROBUST II study investigating the safety and efficacy of a paclitaxel-
coated balloon for the treatment of recurrent urethral strictures.

Methods Subjects were adult men with a single anterior urethral stricture ≤ 3 cm in length and at least 2 prior 
stricture treatments. After treatment with the Optilume urethral drug-coated balloon (DCB), subjects were followed 
through 1 year. The primary safety endpoint was the rate of treatment-related serious complications at 90 days post-
procedure. Efficacy outcomes included symptomatic assessments, erectile function measured using the International 
Index of Erectile Function (IIEF), Qmax, and anatomic success.

Results Sixteen men with an average of 4.1 prior dilations were treated with the DCB. Anatomic success was 
achieved at 6 months in 73%. Average IPSS improved from 18.4 to 6.0 at 1 year (P < 0.001). Qmax improved from  
6.9 mL/sec to 20.8 mL/sec (P < 0.001). There was no change in IIEF. Four subjects received additional treatment within 
1 year. There were no treatment-related serious complications.

Conclusions Short-term follow-up of men with urethral stricture treated with the Optilume DCB showed  
durable anatomic results at 6 months and sustained symptomatic improvement through 1 year. Treatment with  
the device was safe.

Introduction

Urethral stricture disease occurs in approximately 0.6% of men[1]. Formation of scar tissue leads to narrowing of 
the urethral lumen resulting in obstructive lower urinary tract symptoms (LUTS) and associated morbidities that 
negatively impact patient quality of life[1]. Several treatment options are available for stricture, including rigid rod or 
balloon dilation, direct visual urethrotomy (DVIU), and urethroplasty[2]. Although dilation and DVIU are widely 
used for stricture treatment, durability is poor, with long-term stricture-free rates estimated between 8% and 30% 
after a single treatment[3–5]. Furthermore, multiple treatments of the same stricture lead to progressively worse 
outcomes, with success rates approaching 0% at 2 years after a third treatment. Urethroplasty is recommended 
for patients with recurrent strictures or strictures > 2 cm long and has reported success rates > 80% depending on 
approach and stricture characteristics[6].

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mailto:jdelong%40urologyofva.net?subject=SIUJ


Safe and durable minimally invasive solutions for 
stricture treatment are needed given the lack of 
long-term benefit from endoscopic procedures. The 
Optilume urethral drug-coated balloon (Urotronic, 
Inc., Plymouth, MN, US) is the first drug-coated balloon 
(DCB) developed for the management of urethral 
stricture disease. The device combines mechanical 
balloon dilation for immediate symptomatic relief with 
the localized delivery of paclitaxel to maintain long-term 
urethral patency. Paclitaxel acts to inhibit cell division 
thereby preventing new tissue growth and scar tissue 
formation that can lead to stricture recurrence. The 
Optilume DCB was initially evaluated in 53 patients in 
Latin America in the ROBUST I study, which showed 
symptomatic improvement through 2 years after 
treatment in men with urethral strictures ≤ 2 cm long 
and an average of 1.7 prior dilations[7,8]. At 2 years, 
70% of subjects had an improvement in International 
Prostate Symptom Score (IPSS) of at least 50% without 
retreatment[7]. The ROBUST II trial was conducted to 
gain initial experience with the device in the United 
States and in patients with longer strictures (≤ 3 cm).

Materials and Methods
Study Design
ROBUST II is an industry sponsored prospective, 
multicenter, non-randomized, open label study designed 
to assess the safety and efficacy of the Optilume DCB 
for the treatment of anterior urethral stricture at 5 
investigational sites in the United States (ClinicalTrials.
gov: NCT03270384). Institutional review board approval 
was obtained for all study sites.

A baseline retrograde urethrogram was performed 
to obtain urethral and stricture measurements used to 
inform balloon size selection and define stricture char-
acteristics. Balloons with diameters of 18F, 24F, and 30F 
and lengths of 30 and 50 mm were available for use. Per 
physician discretion, strictures were dilated directly 
with the Optilume DCB or pre-dilated with an uncoated 
balloon, rigid rods, or DVIU. The selected DCB was 
inflated to the rated burst pressure and held for at least 
5 minutes (Figure 1). A 12F or 14F Foley catheter was 
inserted after treatment. Subject follow-up occurred at 
Foley removal (2 to 5 days), 30 days, 90 days, 6 months, 
and 1 year.

Study Population
Subjects included adult men with a single anterior 

urethral stricture ≤ 3 cm in length with lumen diameter 
< 12F, at least 2 prior endoscopic treatments of the stric-
ture, bothersome LUTS, IPSS ≥ 13, and peak urinary 
flow (Qmax) < 15 mL/sec. Self-catheterization was not 
considered a prior dilation. Patients were excluded if 
they had prior urethroplasty, radical prostatectomy, 
pelvic radiation, artificial urinary sphincter or urethral 
stent, or stricture dilation or incision within 6 weeks. 
Additional exclusions were diagnosis of lichen sclerosus, 
urinary stone passage within 6 weeks, chronic renal fail-

Abbreviations 
DCB drug-coated balloon
DVIU direct vision internal urethrotomy
IIEF International Index of Erectile Dysfunction
IPSS International Prostate Symptom Score
LUTS lower urinary tract symptoms
PROM patient-reported outcome measure
PVR post-void residual
Qmax peak urinary flow

FIGURE 1. 

DCB alignment utilizing fluoroscopy

a b c

a. Retrograde urethrogram showing bulbar stricture  b. Markers visible across the stricture  c. Balloon inflated across stricture

22 SIUJ  •  Volume 3, Number 1  •  January 2022 SIUJ.ORG

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ure, neurogenic bladder, and history of carcinoma of the 
bladder or prostate within the last 5 years. Eight of the 
16 subjects had exhibited stricture recurrence within 6 
months prior to enrollment. Written informed consent 
was obtained from all subjects prior to study specific 
assessments.

Study Endpoints
The primary safety endpoint was the rate of treat-

ment-related serious complications at 90 days defined 
as a composite of formation of fistula, new strictures 
requiring intervention, unresolved de novo stress 
urinary incontinence requiring > 1 pad/day, and urethral  
rupture. Any change in sexual function was evaluated 
using the “overall satisfaction” domain of the Interna-
tional Index of Erectile Function (IIEF).

Efficacy endpoints included IPSS, anatomic success at 
6 months, a urethral stricture-specific patient-reported 
outcome measure (PROM)[9], Qmax, and freedom from 
repeat intervention. The IPSS responder rate was defined 
as the percent of subjects with ≥ 50% improvement in 
IPSS without repeat treatment. Anatomic success was 
assessed by the ability to pass a 16F flexible cystoscope 
through the treatment site. Subjects re-treated with the 
study device or who received other treatment for their 
stricture prior to the 6-month visit were considered fail-
ures for the anatomic success and repeat intervention 
endpoints.

Pain was assessed using the visual analog scale (VAS) 
before and after treatment. Adverse events were adjudi-
cated by the study medical monitor.

Statistical Methods
An intent-to-treat analysis was performed for all 
endpoints using a complete case approach with no 
imputation for missing data. Descriptive statistics were 
used for data summaries including mean and standard 
deviation for continuous variables and percentages or 
proportions for categorical measures. The significance 
of improvements from baseline were assessed using 
a 2-sided Student t test, in which P < 0.05 indicated 
significance.

Results
The study enrolled 16 subjects from December 2017 
to April 2019, and all were treated with the Optilume 
DCB. Nine subjects completed the 1-year follow-up visit. 
Four subjects exited prior to or at the 6-month visit (3 
treatment failures, 1 withdrawn consent), and 3 did not 
complete the 1-year visit (2 due to COVID-19 pandemic 
and 1 was re-treated with the Optilume DCB just prior 
to the 1-year visit).

Baseline Characteristics and Treatment 
Procedure
The study cohort included men with an average age of 
63.8 years and 4.1 prior dilations of the treated stricture 
(Table 1). Stricture etiology was idiopathic (68.8%), 
traumatic (18.8%), or iatrogenic (12.5%). All subjects had 
bulbar strictures with an average length of 2.1 cm and 
urethral diameter of 2.3 mm. Ten subjects underwent 
direct dilation with the Optilume DCB, and 6 were pre-
dilated with an uncoated balloon or DVIU. The DCB 
diameter used was 30F in 14/16 subjects (87.5%) and 24F 
in 2/16 subjects (12.5%), per surgeon discretion. Subjects 
experienced minimal pain after the procedure, with mean 
VAS scores of 1.7 ± 2.3 at baseline, 2.0 ± 2.0 at treatment, 
1.1 ± 1.2 at Foley removal, and 0.3 ± 0.6 at 30 days.

Safety
A total of 21 adverse events in 10 subjects were reported 
in the study, most frequently urinary tract infection in 
12.5% (2/16) and hematuria in 18.8% (3/16). The majority 
of the events (85.7%, 18/21) were Clavien-Dindo grade 
I-II (Table 2). None of the subjects experienced a serious 
treatment-related complication through 90 days post-
procedure (0/16, 0.0%). Grade III events included 1 event 

23SIUJ.ORG SIUJ  •  Volume 3, Number 1  •  January 2022

One-Year Outcomes of the ROBUST II Study Evaluating the Use of a Drug-Coated Balloon for Treatment of Urethral Stricture

TABLE 1. 

Baseline characteristics and procedure type 

Variable
Mean ± SD or 

n (%)

Age, years 63.8 ± 15.7

Stricture etiology

Iatrogenic 2 (12.5)

Idiopathic 11 (68.8)

Traumatic 3 (18.8)

Stricture measurements

Length, cm 2.1 ± 0.7

Urethral diameter at stricture, mm 2.3 ± 0.9

Urethral diameter distal to stricture, mm 10.5 ± 5.2

Number of prior dilations 4.1 ± 4.9

Procedure Type

Direct DCB dilation 10 (62.5)

 Pre-dilation with uncoated  
balloon or DVIU

6 (37.5)

 Direct DCB dilation with  
post-dilation

0 (0.0)

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each of bronchiectasis, coronary artery stenosis, and 
hematuria (post 3-month urethrogram). All Grade III 
events resolved within 2 weeks of onset, and none were 
related to the study device. There were 4 device-related 
events: 2 mild events of hematuria, 1 case of mild bladder 
spasms, and 1 case of acute urinary retention within 24 
hours of Foley catheter removal. All 4 events resolved 
without sequelae within a month of onset.

There was no negative impact on sexual function 
through 1 year following treatment with the Optilume 
DCB (Table 2). The average IIEF score improved from 
6.7 at baseline to 7.3 at 1 year (P = 0.596).

Efficacy
Efficacy outcome measures showed sustained improve-
ment through 1 year post-procedure (Table 3). The 
average IPSS decreased from 18.4 at baseline to 7.5 at 
90 days, 7.0 at 6 months, and 6.0 at 1 year (P < 0.001). 
The IPSS responder rate was 75.0% (12/16) at 30 days 
and 61.5% (8/13) at 1 year. The average PROM score also 
improved after the procedure, decreasing from 10.8 at 
baseline to 3.6 at 90 days, 4.2 at 6 months, and 4.3 at 1 
year (P < 0.001). Quality of life as measured by IPSS QOL 
improved from 4.4 at baseline to 1.4 at 1 year (P < 0.001).

Voiding function measured by Qmax and post-void 
residual (PVR) urine volume also improved. Average 
peak urinary flow increased from 6.9 mL/sec at baseline 
to 18.9 mL/sec at 3 months, 16.5 mL/sec at 6 months, 
and 20.8 mL/sec at 1 year (P < 0.001). The PVR volume 
improved from 187.1 mL at baseline to 79.3 mL, 59.5 mL, 
and 66.4 mL at 3 months, 6 months, and 1 year respec-
tively, although the decrease was not statistically signifi-
cant (P = 0.134).

The anatomic success rate at 6 months was 73.3% 
(11/15). One subject did not have a cystoscopy performed 
at their 6-month visit and is considered missing for this 
analysis. Of the 13 subjects who completed the 6-month 
cystoscopy, 2 were considered failures. Two additional 
subjects were considered failures due to recurrence 
of their stricture requiring repeat treatment prior to 
the 6-month visit (1 re-treated with Optilume DCB, 
1 urethroplasty). The rate of anatomic success was not 
significantly impacted by the decision to directly dilate 
with the DCB or pre-dilate prior to DCB. The subgroup 
of subjects treated with direct DCB exhibited an 
anatomic success rate of 77.8% (7/9), while the anatomic 
success rate in those subjects receiving pre-dilation with 
uncoated balloon or DVIU was 66.7% (4/6).

A total of 4 subjects received repeat treatment through 
1 year, resulting in a rate of freedom from repeat inter-
vention of 73.3% (11/15). Two subjects were re-treated 
with the DCB, and 2 subjects underwent urethroplasty.

Discussion
Results of the ROBUST II study showed that treatment of 
recurrent anterior urethral stricture with the minimally 
invasive Optilume DCB was safe and achieved durable 
anatomic results at 6 months, with sustained reduction 
in severity of LUTS through 1 year.

The study cohort represents a refractory popula-
tion that is associated with poor endoscopic treatment 

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TABLE 2. 

Adverse events

Adverse Events
Events 

(n)
Subjects 
n/N (%)

Clavien-Dindo Grade 1 10 8/16 (50)

Hematuria 2 2/16 (12.5)

Abdominal pain 1 1/16 (6.3)

Bladder spasm 1 1/16 (6.3)

Flank pain 1 1/16 (6.3)

Oropharyngeal pain 1 1/16 (6.3)

Pelvic pain 1 1/16 (6.3)

Shortness of breath 1 1/16 (6.3)

Urethral false passage 1 1/16 (6.3)

Urinary retention (acute) 1 1/16 (6.3)

Clavien-Dindo Grade 2 8 3/16 (18.8)

Urinary tract infection 4 2/16 (12.5)

Bronchiectasis 1 1/16 (6.3)

Hematuria 1 1/16 (6.3)

Urinary frequency 2 1/16 (6.3)

Clavien-Dindo Grade 3a 1 1/16 (6.3)

Epididymitisa 1 1/16 (6.3)

Clavien-Dindo Grade 3b 2 1/16 (6.3)

Coronary artery stenosisb 1 1/16 (6.3)

Hematuriac 1 1/16 (6.3)

a Pre-existing spermatocele necessitating spermatocelectomy, not 
study-related  b Coronary stent placement prior to 3-month follow-
up, not study-related c Hematuria onset after planned 3-month 
urethrography, not study-related

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One-Year Outcomes of the ROBUST II Study Evaluating the Use of a Drug-Coated Balloon for Treatment of Urethral Stricture

TABLE 3. 

Results summary 

Measure Baseline 30 days 3 months 6 months 1 year

IPSS

n 16 16 16 14 9

Mean ± SD 18.4 ± 4.9 7.2 ± 5.3a 7.5 ± 6.4a 7.0 ± 6.7a 6.0 ± 6.1a

Range 11–28 1–18 1–19 0–19 1–21

Median 18.0 5.5 5.5 4.5 5

IPSS QOL

n 16 16 16 14 9

Mean ± SD 4.4 ± 1.3 1.5 ± 1.5a 1.8 ± 1.8a 1.6 ± 1.5a 1.4 ± 1.5a

Range 3–6 0–5 0–6 0–5 0–4

Median 4.0 1.0 1.0 1.5 1.0

Qmax (mL /sec)

n 16 13 15 13 9

Mean ± SD 6.9 ± 3.7 16.9 ± 8.7a 18.9 ± 16.4a 16.5 ± 10.2a 20.8 ± 9.1a

Range 2.0–14.7 5.9–38.1 4.0–53.0 3.2–37.0 6.0–40.5

Median 5.6 15.0 14.0 18.0 20.0                

PVR (mL)

n 16 16 15 14 9

Mean ± SD 187.1 ± 227.1 84.4 ± 75.5 79.3 ± 80.3 59.5 ± 65.0a 66.4 ± 57.5

Range 0.0–846.0 0.0–254.0 0.0–284.0 0.0–119.0 0.0–186.0

Median 95.0 86.5 61.0 65.0 54.0

PROM

n 16 16 16 13 8

Mean ± SD 10.8 ± 3.4 4.4 ± 4.4a 3.6 ± 3.6a 4.2 ± 3.6a 4.3 ± 4.0a

Range 5–18 0–17 0–12 0–10 0–11

Median 10.5 3.5 3.0 4.0 3.5

IIEF

n 16 16 16 14 9

Mean ± SD 6.7 ± 2.9 6.4 ± 2.9 6.9 ± 3.1 7.5 ± 2.9 7.3 ± 2.8

Range 2–10 2–10 0–10 2–10 2–10

Median 7.0 7.0 7.0 7.0 8.0

Freedom from Repeat NA NA 16/16 13/16 11/15

Intervention, n/N (%) (100.0%) (81.3%) (73.3%)

IPSS Responder Rate NA 12/16 11/16 10/16 8/13

n/N (%) (75.0) (68.8) (62.5) (61.5)

aStatistically significant improvement from baseline (P < 0.05)

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outcomes. Subjects had moderate-to-severe LUTS at 
baseline with an IPSS of 18.4. The majority of subjects 
(81.3%) had strictures that were ≥ 2 cm long; for these 
patients, current guidelines recommend urethroplasty 
as initial treatment given low success rates of dilation 
or DVIU[6]. All subjects had at least 2 prior dilations of 
the treated stricture and an average of 4.1 prior interven-
tions, meaning treatment with the Optilume DCB repre-
sented the fifth dilation of the stricture on average.

Symptom severity as measured by IPSS decreased to 
6.0 at 1 year, indicating that subjects were experienc-
ing mild symptoms post-treatment. This represents an 
average improvement in IPSS of 12.4 points (67.4%) and 
is clinically meaningful based on a minimal clinically 
important difference of 6 points for patients with severe 
LUTS[10]. Changes in the PROM score for anterior 
urethral stricture mirrored the IPSS, with an average 
of 10.8 at baseline improving to 4.3 at 1 year, repre-
senting a change of 60.2%. Improvement in subjective 
symptom measures were accompanied by improvement 
in objective measures of voiding function. The average 
Qmax improved 201.4%, from 6.9 mL/sec at baseline 
to 20.8 mL/sec at 1 year (P < 0.001). Peak flow at 1 year 
was higher than the 15 mL/sec typically used to define 
patients free from clinically significant stricture recur-
rence. Further, the observed reductions in PVR urine 
volume showed that more complete voiding could be 
achieved after treatment with the Optilume DCB.

Flexible cystoscopy demonstrated an anatomic 
success rate of 73% at 6 months. Despite these subjects 
having longer stricture lengths and a higher number of 
prior failed treatments, this was similar to the anatomic 
success rate previously reported in ROBUST I of 76% at 
the same time point[8]. In contrast, published success 
rates for dilation or urethrotomy after 3 repeat dilations 
is around 20% to 30% at 6 months, which decreases to 0% 
at 24 months[3,5]. Median time to stricture recurrence 
with endoscopic treatment is 6 to 12 months; for patients 
with 3 treatments, the median time to recurrence has 
been reported to be about 4.5 months[3]. Results for the 
initial 6-month period following treatment are criti-
cal because a hazard function analysis showed that the 
risk of stricture recurrence after endoscopic treatment 
is greatest at 6 months[11]. The 6-month timepoint was 
therefore chosen in this study to assess anatomic success.

Data collected to date support the safety of the device 
and procedure. Adverse events were generally mild and 
resolved shortly after onset. Most events were associated 
with urethral stricture disease or were common post 
urinary intervention. Erectile function was not affected 
by treatment.

The advantages of dilation or DVIU are hampered 
by low long-term success rates. Multiple groups have 

investigated the use of antifibrotic agents to augment 
traditional urethrotomy in an attempt to achieve the 
durability of open urethroplasty[12]. Two small random-
ized controlled trials have investigated urethrotomy 
with or without triamcinolone intralesional injection 
with mixed results; one study showed a lower rate of 
stricture recurrence in the triamcinolone treated group 
and the other study showed no difference between 
groups in the rate of stricture recurrence[13,14]. Mito-
mycin C as well as hyaluronic acid and carboxymethyl-
cellulose have also been evaluated in small randomized 
controlled trials showing encouraging results, although 
long-term follow-up is lacking and the safety of mitomy-
cin C has recently been questioned[15–18]. Indeed, even 
the combination of all 3 drugs has been proposed as a 
potential treatment[19]. To date, there is a lack of robust 
evidence to support adjunctive treatment with steroids, 
mitomycin C, or hyaluronidase. One potential advan-
tage of a drug-coated balloon is the ability to deliver the 
drug more evenly around the circumference and along 
the length of the stricture, as compared with multiple 
manual injections of antifibrotic agents.

The Optilume DCB procedure is minimally invasive, 
has low complication rates, and leverages current meth-
ods of treating stricture. The potential to treat longer 
strictures with minimally invasive procedures would 
allow more patients access to interventions with intent-
to-cure and with lower associated morbidity. In contrast 
to ROBUST I, subjects in ROBUST II could undergo 
direct DCB treatment without prior stricture dilation 
with an uncoated balloon or DVIU. The rate of anatomic 
success at 6 months for subjects treated directly with 
the DCB was similar to the rate for those treated with 
pre-dilation. Data reported previously in an animal 
model show urethral concentration of paclitaxel drop-
ping by 73% at 7 days post-procedure, and low serum 
levels at all time points[7].

There were several important limitations in this early 
phase study. The open label study lacked a control arm, 
and the sample size was small. Patients with higher 
risk of stricture recurrence, including those with blad-
der neck contractures, prior radiotherapy, or lichen 
sclerosus were excluded from the study; it is unknown 
how the DCB treatment would have performed in these 
subgroups. This small study was intended as an initial 
evaluation of the safety and efficacy of the therapy in 
the United States before initiation of the ROBUST III 
randomized controlled pivotal trial which is ongoing. 
Finally, while the 1-year outcomes of this study are 
encouraging, longer follow-up is required to assess treat-
ment durability with the Optilume DCB. Follow-up is 
expected up to 5 years and results from ROBUST I have 
already shown a functional treatment success rate of 
70% at 2 years[7].

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Conclusions
Early results of the ROBUST II study showed that 
treatment of recurrent male anterior urethral stricture 
with the Optilume DCB was safe and showed durable 

anatomic results at 6 months and sustained symptomatic 
improvement through 1 year. Data are preliminary, and 
follow-up to 5 years is planned.

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18. Redshaw JD, Broghammer JA, Smith TG, 3rd, Voelzke BB, Erickson 
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19. Kumar S, Garg N, Singh SK, Mandal AK. Efficacy of optical internal 
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27SIUJ.ORG SIUJ  •  Volume 3, Number 1  •  January 2022

One-Year Outcomes of the ROBUST II Study Evaluating the Use of a Drug-Coated Balloon for Treatment of Urethral Stricture

http://SIUJ.org

