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More Endoscopy-Based Brushing Passes Improve the Detection of Malignant Biliary Strictures: A Multicenter Randomized Controlled Trial

Wang, Junjun MD1,*; Xia, Mingxing MD2,*; Jin, Yubiao MD3,*; Zheng, Haiming MD4; Shen, Zhenyang MD1; Dai, Weiming MD1; Li, Xiaoman MD1; Kang, Mei MD5; Wan, Rong MD1; Lu, Lungen MD1; Hu, Bing MD2; Wan, Xinjian MD4; Cai, Xiaobo MD1

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The American Journal of Gastroenterology: May 2022 - Volume 117 - Issue 5 - p 733-739
doi: 10.14309/ajg.0000000000001666
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Malignant biliary strictures (MBSs) are usually caused by biliary carcinomas or other adjacent organ malignancies, such as pancreatic cancer. Because of the limitations of abdominal imaging, diagnosing MBSs is still challenging, and up to 20% of biliary strictures remain indeterminate before the eventual diagnosis (1). Endoscopic retrograde cholangiopancreatography (ERCP)–based sampling plays an important role in the diagnosis of MBSs and guides further therapies. ERCP-based brush cytology remains the first-line approach for sample acquisition because of its simplicity, safety, low cost, and high specificity. However, the average sensitivity of brush cytology is only approximately 40%, based on the reported studies (2). According to these reports, the sensitivity varied from 33% to 60% (3–5). Despite the different causes or characteristics of MBSs, brushing procedures of endoscopists may also lead to variation of results. Brush-based advanced molecular techniques have been studied for use in the diagnosis of MBSs. Fluorescent in situ hybridization (FISH), which uses fluorescent-labeled DNA probes to assess specific DNA sequences, has been widely studied and has significantly increased the detection of pancreatobiliary malignancies compared with that of conventional brush cytology (6,7).

There is still no consensus on ERCP-based brushing. Endoscopists commonly brush the stricture back and forth approximately 10 times (2). In theory, increasing the chances of acquiring specimens may promote the sensitivity of brush cytology. Thus, a second brushing was reported to improve cancer detection (8). However, this would require instrument exchanges, which may increase not only the burden on endoscopists but also the risk of infection. Increasing the number of brushing passes during a single brushing may have a similar effect of increasing the number of acquired specimens, and it is easy to perform because it does not require device exchanges; however, this hypothesis has not been reported in the literature.

To elucidate this, we initiated a multicenter randomized trial to investigate whether the number of brushing passes affects the detection rate of malignancy in MBSs.


Study population and design

This randomized controlled trial was performed at 3 tertiary endoscopy centers in China. This study complied with the Declaration of Helsinki and the SPIRIT 2013 Statement. Patients aged 18–89 years with biliary strictures that were highly suspected of malignancies based on clinical data and enhanced abdominal computed tomography/magnetic resonance imaging and magnetic resonance cholangiopancreatography who underwent ERCP were included in this study. Each patient was oriented by a multidisciplinary team composed of experienced radiologists, surgeons, and endoscopists before inclusion. The exclusion criteria included failure of cannulation, contraindications for ERCP, known malignancy unrelated to MBSs, coagulation dysfunction, and severe cardiac or pulmonary dysfunction. The study protocol was approved by the ethics committee of each hospital, and informed consent was obtained from all patients (, identifier: ChiCTR1800015978) (see Supplementary Materials, Supplementary Digital Content 2,

Randomization and masking

Eligible patients were randomly assigned (1:1:1) to receive 10, 20, or 30 brushing passes for a biliary stricture. An independent statistician performed randomization using a computer-generated randomization list stratified by the center. The principal investigator from each center enrolled and assigned participants. Endoscopists, investigators responsible for enrollment and follow-up, and statisticians were not blinded to group allocation, whereas pathologists, outcome assessors, and patients were blinded to the brush assignment.


All patients were hospitalized and received intravenous conscious sedation or general anesthesia during ERCP according to the established standards at each center. All procedures were performed by experienced endoscopists (>300 ERCP procedures per year). Patients routinely received preinterventional antibiotics intravenously. After routine cholangiogram and determination of the location and length of the stricture, a brush catheter was advanced proximal to the stricture along the guide wire. Whether sphincterotomy was performed was based on the decision of endoscopists. The brush was then advanced from the catheter across the stricture and passed back and forth across the stricture 10, 20, or 30 times (1 time including a round of passes from back to forth and then forth to back), according to the patient assignment. The first brushing was monitored under x-ray, and x-ray was not applied until the completion of brushing if the brush successfully moved. The brush was then withdrawn into the catheter and pulled out from the endoscope as a unit, and the brush was then cut and placed into a fixative solution. Additional 2–3 mL fixative solution saline was injected into the catheter to drain the remaining liquid coming from the movement of the brush, which was included in the brush cytology. The same type of cytology brush (RX Cytology Brush; Boston Scientific, Marlborough, MA) was used in each center, and all endoscopists were educated and performed stricture brushing in the same way. Biliary drainage was then performed using a nasobiliary tube or stent at the discretion of the endoscopist. Adverse events, including post-ERCP pancreatitis (PEP), bleeding, and acute cholangitis, were assessed 24 and 48 hours after the procedure.

The biliary cytology results were classified as “nonmalignant,” “atypical,” “suspicious,” or “malignant.” The cytology results were considered positive for malignancy when the reports indicated either “suspicious” or “malignant.” In some patients, FISH was also performed using standard protocols and commercially available probes specific to centromeres of chromosomes 3, 7, and 17 in one hybridization and P16 in the second hybridization. The test was considered positive if the specimen was positive for either polysomy or P16 deletion.


MBSs were determined by cytology or histology on tissue sampling during the initial or subsequent ERCP procedure, endoscopic ultrasonography-fine needle aspiration (EUS-FNA), or by surgical specimens. Because some patients with MBSs lacked indications for surgery at the time of diagnosis and the sensitivity of brush cytology was unsatisfactory, malignancy can also be diagnosed clinically if the patients had malignant outcomes, such as tumor invasion, metastasis, and dyscrasia, or died of malignancy-related complications during the follow-up. The primary outcome was the sensitivity and specificity of brush cytology in different groups, which was assessed at 6 months after the initial ERCP procedure. The secondary outcome was the technical success of brushing, and safety outcomes including PEP, cholangitis bleeding, and perforation were also evaluated. PEP was defined as follows: new or worsened abdominal pain with elevated serum amylase level >3-fold of the upper limit of normal for 24 hours after ERCP that required at least 2 days of hospitalization. Meanwhile, post-ERCP cholangitis was defined as a body temperature of ≥38 °C, leukocytosis (white blood cell count ≥10 × 109/L), and clinical manifestations of cholangitis after ERCP. Postoperative bleeding was defined as clinical evidence of bleeding, such as melena or hematemesis, with at least a 2-g/dL decrease in the hemoglobin level or the need for a blood transfusion. Perforation was defined as evidence of air or luminal contents outside the gastrointestinal or biliary tract (9). Patients were contacted again at 30 days after ERCP to assess for delayed complications. The FISH test was updated as an exploratory outcome after study initiation.

Statistical analysis

Based on previous reports, the average sensitivity of brush cytology when performed 10 times was 0.42 (2). Meanwhile, our pilot study showed a sensitivity of 0.33, 0.50, and 0.68 when brushing for MBSs was performed 10, 20, and 30 times (data unpublished). Thus, 150 patients were needed in each group to detect a difference between the groups, with a prevalence of 85% for MBSs and a power of 80% at a statistical significance level of 0.05 (2-sided).

Continuous variables were expressed as mean ± SD or median (interquartile range) and were tested for normality distribution using the Kolmogorov-Smirnov test. Dichotomous variables are presented as frequencies (%). For normally distributed variables, an analysis of the variance test was performed; otherwise, the Kruskal-Wallis H test was performed. The χ2 test or Fisher test was used to compare categorical variables among all groups. The Bonferroni method was used for pairwise comparisons of the groups. Sensitivity and specificity were used to evaluate the diagnostic value of brush cytology or FISH measurements with different brushing frequencies. Multivariate logistic regression analysis was performed to determine the independent factors related to the increased sensitivity of brush cytology after adjusting for the contributions of other variables.

All reported P values of less than 0.05 were deemed to be significant. All analyses were performed using the R Project for Statistical Computing (version 4.0.5). This trial was registered with (no. ChiCTR1800015978).



Between June 1, 2018, and July 31, 2020, 663 consecutive patients with suspected MBSs scheduled for ERCP were assessed for eligibility; 213 patients were excluded from the screening. The remaining 450 patients were randomly assigned to undergo endoscopic biliary brushing that was to be performed 10, 20, or 30 times in 1 specimen. Seven patients withdrew consent after the ERCP procedure, and 443 patients were finally included in the intention-to-treat analysis: 147, 148, and 148 patients in the 10-times, 20-times, and 30-times groups, respectively. A total of 137, 139, and 141 patients were finally diagnosed with malignancy after the follow-up in the 10-times, 20-times, and 30-times groups, respectively (Figure 1). Among the patients diagnosed with cancer, 58 patients underwent surgery and confirmed malignancy histologically. A total of 238 patients were diagnosed by EUS-FNA, brush cytology, or biliary biopsy. The remaining 121 patients (29%) were clinically diagnosed malignancy based on the nonhistological evidence during the follow-up. The baseline characteristics were similar among the 3 groups. Cholangiocarcinoma and pancreatic cancer were the most common causes of MBSs (Table 1).

Figure 1.:
Patient flow diagram. ERCP, endoscopic retrograde cholangiopancreatography.
Table 1.:
Baseline clinical and endoscopic characteristics in the enrolled patients

Study outcome

The primary endpoint of brush cytology sensitivity was compared among the 3 groups. The sensitivity was 38%, 47%, and 57% in the 10-times, 20-times, and 30-times groups, respectively, which was statistically significant (P = 0.005), and the 30-times group showed a significantly higher sensitivity than the 10-times group (P = 0.001). However, the sensitivity in the 20-times group was not significantly different from those of the 10-times and 30-times groups (P = 0.139 and P = 0.074, respectively). The specificity was not statistically different among the 3 groups, which were 0.90, 1.00, and 1.00 in the 10-times, 20-times, and 30-times groups, respectively (Table 2).

Table 2.:
Sensitivity and specificity of brush cytology in the enrolled patients

The definition of positive cytology results for malignancy in this study included both “suspicious” and “malignant.” Therefore, we also performed sensitivity analysis when suspicion for malignancy was not included. There were 19, 28, and 41 patients who reported malignant results, and the sensitivity was 0.14, 0.21, and 0.30 in 10-times, 20-times, and 30-times groups, respectively (see Supplementary Table 1, Supplementary Digital Content 1, To avoid the incorporation bias, we also analyzed the sensitivity after excluding the patients who were clinically diagnosed with malignancy and the absence of pathological evidence. The sensitivity was 0.56, 0.68, and 0.76 in 10-times, 20-times, and 30-times groups, respectively, and the significance was still achieved between 10-times and 30-times groups (P = 0.004) (see Supplementary Table 2, Supplementary Digital Content 1, We also performed sensitivity analysis for the individual center, and the results were similar (see Supplementary Table 3, Supplementary Digital Content 1,

In the 10-times, 20-times, and 30-times groups, 47, 120, and 101 patients underwent FISH testing, which resulted in a sensitivity of 0.58, 0.68, and 0.70 and a specificity of 0.75, 0.67, and 0.80, respectively. No statistical difference was found between the groups (Table 3). Multivariate analysis in patients with MBSs indicated that a longer stricture length was related to positive brush cytology results (odds ratio 1.254; 95% confidence interval 1.046–1.503, P = 0.015), and brushing 30 times was an independent factor for a higher sensitivity of brush cytology (odds ratio 2.082; 95% confidence interval 1.271–3.411, P = 0.004) (Table 4).

Table 3.:
Sensitivity and specificity of fluorescent in situ hybridization
Table 4.:
Logistic regression analysis of factors related to the increased sensitivity of brush cytology in patients with malignant biliary strictures (n = 417)

All 3 groups showed 100% technical success in brushing. However, the handle of the brush was damaged during the brushing process in 4 cases (2.7%) in the 30-times group, and 3 of them were used for distal biliary strictures, although the procedures were still completed. No brushes were damaged in the 10-times and 20-times groups. For procedure-related complications, they occurred in 52 of the 443 patients (11.7%). Cholangitis and pancreatitis were the most common complications with an incidence of 5.6% and 4.5%, respectively. However, the incidence of pancreatitis, cholangitis, or bleeding did not differ among the 3 groups, and no perforation was found in the 3 groups (Table 5).

Table 5.:
Secondary endpoint and safety outcomes in the enrolled patients


Pathology remains the gold standard for the diagnosis of MBS. Endobiliary forceps biopsy under x-ray guidance, peroral cholangioscopy, and EUS-FNA have also been applied for the diagnosis of MBSs (10–13). However, ERCP-based brushing, which is safe, simple, and relatively inexpensive, is the most widely used technique for the diagnosis of MBSs. Although the reported specificity of brush cytology was nearly 100%, the sensitivity was only approximately 40%, which put it in an embarrassed status because other endoscopic techniques or devices for the diagnosis of MBSs have been developed in recent years. Advanced molecular technologies based on brushing samples, such as FISH and next-generation sequencing, have been reported to increase sensitivity. A recent study showed that the sensitivity and specificity of next-generation sequencing for MBSs were 73% and 100%, respectively, which were significantly higher than those of serum CA19-9 levels and pathological evaluation (14). However, these newly developed molecular diagnostic methods have not been widely applied and cannot replace the gold standard provided by pathology.

Biliary brushing is currently regarded as the first-line approach for the diagnosis of MBSs, and novel brushes have also been studied to improve the low sensitivity. A novel endoscopic device with scraping loops was developed in Japan and showed significantly higher cancer detectability than that of biopsy forceps (64.7% vs 51.3%) (15). However, the application of these novel brushes may require time.

The reported results of traditional brushing varied from 30% to 60%, which may be partly explained by brushing skills or procedures. Until now, no consensus or guidelines for ERCP-guided brushing have been established. The most commonly applied method for brushing was to advance the brush from the catheter across the stricture and move it back and forth across the stricture 10 times (2). The brush destroys the tumor surface, which allows the collection of malignant cells through the movement of the brush. In theory, increased exfoliation may lead to better specimen cellularity and higher diagnostic yield. Therefore, more brushing passes may theoretically improve the detection rate. Multiple brushing specimens have been reported to improve cancer detection rates (8). However, repeated brushing requires more frequent instrument exchanges, making the procedure more complicated and increasing the chances of biliary infection. Therefore, a higher number of brushing passes for 1 brush specimen may be a better choice to improve the sensitivity.

Therefore, we randomly performed 10, 20, or 30 biliary brushing times in the included patients. Our results demonstrated that the sensitivity of malignancy detection increased as the number of brushing passes increased, and brushing 30 times showed a higher sensitivity than that of 10 times (57% vs 38%). Brushing 20 times also showed a higher sensitivity (47%) than the 10 times group. However, the significance was not achieved, maybe because of the limited sample size. Although brushing 30 times could be more time-consuming, it may only take additional 20–30 seconds. Therefore, brushing 30 times could be more cost-effective. The characteristics of strictures may also influence the detection rate of brushes. Our results showed that a longer stricture length was related to the detection of malignancy by brush cytology, which is understandable.

Although brushing 30 times could promote the sensitivity of cytology than conventional 10 times, the result was still not satisfying. The design of the brush like a small caliber and only to-and-fro movement may acquire limited cells from the tumor surface. The fibrosis or ulceration of the stricture could further restrict the efficiency of sampling. Therefore, further brush-based advanced molecular techniques could be a complementary approach for the diagnosis. In our study, some patients also underwent the FISH test, and the results demonstrated that the 20-times and 30-times groups tended to have a higher sensitivity than the 10-times group, but the difference was not statistically significant (0.68 and 0.70 vs 0.58). This is also understandable because FISH is more sensitive than brush cytology and requires less malignant cells for a positive diagnosis. Because only part of the patients accepted the FISH test, we did not analyze the diagnostic sensitivity by combining the 2 methods. However, further studies are needed to elucidate this issue.

Because some patients with MBSs lacked indications for surgery at the time of diagnosis and the sensitivity of brush cytology was unsatisfactory, malignancy can also be diagnosed clinically if the patients had malignant outcomes or evidence during the follow-up, which may cause incorporation bias. Therefore, we also analyzed the sensitivity only in patients with pathological evidence was also analyzed and the results still support brushing 30 times. Our results also showed that more brushing passes did not increase the incidence of procedure-related complications, such as bleeding, cholangitis, pancreatitis, and perforation. Therefore, brushing 30 times can be safely performed.

Our study had some limitations. First, the sample size in our study was not large. However, according to our sampling calculation, the number of the enrolled patients was met in our study. Second, the maximal brush time was 30 times in our study. Although more brushing times may further increase the sensitivity, it is more time-consuming and can cause damage to the instruments. In fact, 4 brushes in the 30-times group were damaged during the procedure, although the brushing processes were completed. Therefore, we believed brushing 30 times may be enough.

In conclusion, our results showed that ERCP-based brushing of 30 times for 1 specimen was safe, easily performed, and may increase the detection rate for MBSs. Further large-scale studies are necessary to confirm our findings.


Guarantor of the article: Xiaobo Cai, MD, PhD.

Specific author contributions: J.W.: drafted the article and collected and interpreted the data. M.X.: performed the procedure and collected data. Y.J.: collected and interpreted data. H.Z.: performed the procedure and collected data. Z.S., W.D., X.L., and R.W.: collected and interpreted data. L.L.: revised the article. M.K.: analyzed data. B.H.: planned the study and approved the article. X.W.: planned the study and approved the article. X.C.: planned and conducted the study, interpreted data, critically revised the article, and made the final approval of the article.

Financial support: This study was supported by the Clinical Research Innovation Plan of Shanghai General Hospital, China (CTCCR-2019C07).

Potential competing interests: None to report.

Study Highlights


  • ✓ Endoscopic brush cytology remains the first-line method for the diagnosis of malignant biliary strictures.
  • ✓ The sensitivity of brush cytology is unsatisfactory.
  • ✓ The reported sensitivity of brush cytology varies, and no consensus on brushing times in 1 specimen has been established.


  • ✓ Brushing 30 passing times in 1 specimen could significantly improve the sensitivity of brush cytology than that 10 times.
  • ✓ Brushing 30 times could be successfully performed without increasing the procedure-related complications.


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