Overexpression of enhancer of zeste homolog 2 and MUC1 may be related to malignant behaviour in intraductal papillary neoplasm of the bile duct

A Review of Type 1 and Type 2 Intraductal Papillary Neoplasms of the Bile Duct

Intraductal papillary neoplasm of the bile duct (IPNB) is a heterogeneous disease similar to intraductal papillary mucinous neoplasm of the pancreas. These lesions have been recognized as one of the three major precancerous lesions in the biliary tract since 2010. In 2018, Japanese and Korean pathologists reached a consensus, classifying IPNBs into type l and type 2 IPNBs. IPNBs are more prevalent in male patients in East Asia and are closely related to diseases such as cholelithiasis and schistosomiasis. From a molecular genetic perspective, IPNBs exhibit early genetic variations, and different molecular pathways may be involved in the tumorigenesis of type 1 and type 2 IPNBs. The histological subtypes of IPNBs include gastric, intestinal, pancreaticobiliary, or oncocytic subtypes, but type 1 IPNBs typically exhibit more regular and well-organized histological features than type 2 IPNBs and are more commonly found in the intrahepatic bile ducts with abundant mucin. Due to the rarity of these lesions and the absence of specific clinical and laboratory features, imaging is crucial for the preoperative diagnosis of IPNB, with local bile duct dilation and growth along the bile ducts being the main imaging features. Surgical resection remains the optimal treatment for IPNBs, but negative bile duct margins and the removal of lymph nodes in the hepatic hilum significantly improve the postoperative survival rates for patients with IPNBs.

Biliary Tract Cancer: Molecular Biology of Precursor Lesions

Biliary tract cancer is a devastating malignancy of the bile ducts and gallbladder with a dismal prognosis. The study of precancerous lesions has received considerable attention and led to a histopathological classification which, in some respects, remains an evolving field. Consequently, increasing efforts have been devoted to characterizing the molecular pathogenesis of the precursor lesions, with the aim of better understanding the mechanisms of tumor progression, and with the ultimate goal of meeting the challenges of early diagnosis and treatment. This review delves into the molecular mechanisms that initiate and promote the development of precursor lesions of intra- and extrahepatic cholangiocarcinoma and of gallbladder carcinoma. It addresses the genomic, epigenomic, and transcriptomic landscape of these precursors and provides an overview of animal and organoid models used to study them. In conclusion, this review summarizes the known molecular features of precancerous lesions in biliary tract cancer and highlights our fragmentary knowledge of the molecular pathogenesis of tumor initiation.

EZH2 Promotes Cholangiocarcinoma Development and Progression through Histone Methylation and microRNA-Mediated Down-Regulation of Tumor Suppressor Genes

Cholangiocarcinoma (CCA) is a highly malignant cancer of the biliary tree. Although studies have implicated enhancer of Zeste homolog 2 (EZH2) in CCA growth, the role of EZH2 in CCA development has not been investigated, and the mechanism for EZH2-regulated gene expression in CCA remains to be further defined. The current study used a mouse model of CCA induced by hydrodynamic tail vein injection of Notch1 intracellular domain and myristoylated-AKT plasmids. Mice with liver-specific EZH2 knockout displayed reduced CCA development. In a xenograft model, EZH2 knockdown significantly decreased CCA progression. Administration of the EZH2 inhibitor GSK126 decreased CCA tumor burden in mice. Accordingly, EZH2 depletion or inhibition reduced the growth and colony formation capability of CCA cells. Analysis of high-throughput data identified a set of 12 tumor-inhibiting genes as targets of EZH2 in CCA. The experimental results suggest that EZH2 may down-regulate these tumor-inhibiting genes through methylation of lysine 27 on histone H3 (H3K27) in the gene louses and through regulation of specific miRNAs. High mobility group box 1 was shown to facilitate the methyltransferase activity of EZH2, which is implicated in the regulation of CCA cell growth. The study shows that EZH2 promotes CCA development and progression through a complicated regulatory network involving tumor-inhibiting genes, miRNAs, and high mobility group box 1, which support targeting EZH2 as a potentially effective strategy for CCA treatment.

An immunohistochemical panel of insulin-like growth factor II mRNA-binding protein 3 (IMP3), enhancer of zeste homolog 2 (EZH2), and p53 is useful for a diagnosis in bile duct biopsy

Bile duct biopsy is being increasingly performed in number for a definite diagnosis of cholangiocarcinoma. However, difficulties are associated with a histopathological diagnosis because of the limited small amount of specimen obtained and crash artifact. The aim of the present study was to identify useful diagnostic immunohistochemical markers in bile duct biopsy that support a histological diagnosis. Fifty-one bile duct biopsy samples, including 26 samples taken from patients with cholangiocarcinoma, 11 with intraductal papillary neoplasm of the bile duct (IPNB), and 14 with benign bile duct lesions, were examined. Histology and the immunohistochemical expression of insulin-like growth factor II mRNA-binding protein 3 (IMP3), enhancer of zeste homolog 2 (EZH2), and p53 were assessed. They were then evaluated for their usefulness as diagnostic markers of malignancy. The diagnostic sensitivity and accuracy of the institutional histological diagnosis were 53.8% and 70.0%, respectively. The diagnostic sensitivity and accuracy of IMP3, EZH2, and p53 were 69.2% and 80.0%, 76.9% and 85.0%, and 50.0% and 67.5%, respectively. Immunohistochemical staining for EZH2; the combination of either 2 of IMP3, EZH2, and p53; or the combination of IMP3, EZH2, and p53 significantly increased sensitivity and accuracy over those of the institutional histological diagnosis (p<0.05). In conclusion, an immunohistochemical panel consisting of IMP3, EZH2, and p53 increases the diagnostic sensitivity and accuracy of bile duct biopsy for the diagnosis of cholangiocarcinoma.

Application of enhancer of zeste homolog 2 immunocytochemistry to bile cytology

BACKGROUND

Bile cytology has low diagnostic sensitivity and requires ancillary techniques. This study assessed the utility of enhancer of zeste homolog 2 (EZH2) immunocytochemistry (ICC) in bile cytology.

METHODS

A total of 141 bile cytology specimens from 141 patients were evaluated retrospectively. Papanicolaou-stained slides were immunostained with an antibody to EZH2. After calculation of the EZH2 labeling index (LI), the cutoff value was determined via receiver operating characteristic curve analysis. Cytological performance with and without EZH2 ICC was evaluated with reference to the final diagnosis.

RESULTS

The area under the curve for the EZH2 LI was 0.955, and the cutoff value for identifying benign bile samples versus malignant ones was 24.0%. The sensitivity and specificity values for malignancy were 53.4% and 100% for routine cytology only, 89.0% and 95.7% for EZH2 ICC only, and 89.8% and 95.7% for a combination of routine cytology and EZH2 ICC. The sensitivities of EZH2 ICC only and a combination of routine cytology and EZH2 ICC were significantly improved in comparison with routine cytology only (P < .001). EZH2 ICC alone had a sensitivity of 68.0% and a specificity of 85.7% in bile samples with atypical cytology, a sensitivity of 87.0% in samples that were suspicious for malignancy, and a sensitivity of 85.7% and a specificity of 100% in samples that were negative for malignancy.

CONCLUSIONS

EZH2 ICC improved the diagnostic sensitivity for pancreatobiliary adenocarcinoma in bile cytology. This method is particularly meaningful in samples of indeterminate cytology and may be useful as an initial assessment to ensure that no cancer cells are missed.

Cystic biliary tumors of the liver: diagnostic criteria and common pitfalls

With major advancements and frequent use of abdominal imaging techniques, hepatic cysts are increasingly encountered in clinical practice. Although the majority of cysts are benign, a small subset represents neoplastic precursors to cholangiocarcinoma. These cystic precursors include intraductal papillary neoplasms of the bile duct (IPNB) and mucinous cystic neoplasms of the liver (MCN-L), and bear striking pathologic resemblance to corresponding cystic neoplastic precursors within the pancreas. This review examines the salient clinical, gross, microscopic and molecular features of IPNBs and MCN-Ls, and, in particular, provides histopathologic comparison to their pancreatic counterparts. Considering these neoplasms may be diagnostically challenging, we also discuss other hepatic lesions within the differential diagnosis, and the potential for molecular methods to improve their preoperative evaluation and the early detection of cholangiocarcinoma.

Intraductal Papillary Neoplasm of Bile Duct: Updated Clinicopathological Characteristics and Molecular and Genetic Alterations

Intraductal papillary neoplasm of the bile duct (IPNB), a pre-invasive neoplasm of the bile duct, is being established pathologically as a precursor lesion of invasive cholangiocarcinoma (CCA), and at the time of surgical resection, approximately half of IPNBs show stromal invasion (IPNB associated with invasive carcinoma). IPNB can involve any part of the biliary tree. IPNB shows grossly visible, exophytic growth in a dilated bile duct lumen, with histologically villous/papillary neoplastic epithelia with tubular components covering fine fibrovascular stalks. Interestingly, IPNB can be classified into four subtypes (intestinal, gastric, pancreatobiliary and oncocytic), similar to intraductal papillary mucinous neoplasm of the pancreas (IPMN). IPNBs are classified into low-grade and high-grade based on lining epithelial features. The new subclassification of IPNB into types 1 (low-grade dysplasia and high-grade dysplasia with regular architecture) and 2 (high-grade dysplasia with irregular architecture) proposed by the Japan–Korea pathologist group may be useful in the clinical field. The outcome of post-operative IPNBs is more favorable in type 1 than type 2. Recent genetic studies using next-generation sequencing have demonstrated the existence of several groups of mutations of genes: (i) IPNB showing mutations in KRAS, GNAS and RNF43 belonged to type 1, particularly the intestinal subtype, similar to the mutation patterns of IPMN; (ii) IPNB showing mutations in CTNNB1 and lacking mutations in KRAS, GNAS and RNF43 belonged to the pancreatobiliary subtype but differed from IPMN. IPNB showing mutation of TP53, SMAD4 and PIK3CA might reflect complicated and other features characterizing type 2. The recent recognition of IPNBs may facilitate further clinical and basic studies of CCA with respect to the pre-invasive and early invasive stages.

CK20 and lymph node involvement predict adverse outcome of malignant intraductal papillary neoplasm of the bile duct

OBJECTIVES

To identify prognostic factors of malignant intraductal papillary neoplasm of the bile duct (m-IPNB).

MATERIALS AND METHODS

We included 38 consecutive cases which underwent surgical resection and diagnosed as IPNB with malignant component from January 2003 to January 2017. Clinicopathological variables were collected to conduct survival analysis and identify prognostic factors.

RESULTS

The median overall survival (OS) of m-IPNB was 76.0 months, with 1-, 3-, and 5-year survival rates of 97.2%, 73.5%, and 59.8%, respectively. The median RFS was 48.0 months with 1-, 3-, and 5-year recurrence-free survival (RFS) rate was 83.2%, 59.8%, and 44.6%, respectively. Univariate analysis showed that elevation of carcinoembryonic antigen CEA, lymph node involvement, resection margin status, degree of periductal invasion, and positive expression of CK20 were associated with both OS and RFS of m-IPNB. After multivariate Cox models analysis, lymph node involvement and positive expression of CK20 were identified as independent prognostic factors for OS, while lymph node involvement and resection margin status were independent prognostic factors for RFS. The median OS of patients with m-IPNB involving lymphatic metastases and positive expression of CK20 was 27.0±8.8 months and 51.0±12.4 months, respectively. The median RFS of cases with lymph node involvement and R1 resection was 10.0±3.3 months and 25.0±6.9 months, respectively. However, there was no significant difference in OS or RFS between cases of pancreaticobiliary and intestinal subtype.

CONCLUSIONS

Lymph node involvement and positive expression of CK20 are independent prognostic factors for shorter OS of m-IPNB, while patients with lymph node involvement and positive resection margin are at higher risk of tumor recurrence.

Extracellular Vesicles in Hepatobiliary Malignancies

Primary hepatobiliary malignancies include a heterogeneous group of cancers with dismal prognosis, among which hepatocellular carcinoma (HCC), cholangiocarcinoma (CCA), and hepatoblastoma (HB) stand out. These tumors mainly arise from the malignant transformation of hepatocytes, cholangiocytes (bile duct epithelial cells) or hepatoblasts (embryonic liver progenitor cells), respectively. Early diagnosis, prognosis prediction and effective therapies are still a utopia for these diseases. Extracellular vesicles (EVs) are small membrane-enclosed spheres secreted by cells and present in biological fluids. They contain multiple types of biomolecules, such as proteins, RNA, DNA, metabolites and lipids, which make them a potential source of biomarkers as well as regulators of human pathobiology. In this review, the role of EVs in the pathogenesis of hepatobiliary cancers and their potential usefulness as disease biomarkers are highlighted. Moreover, the therapeutic value of EV regulation is discussed and future directions on basic and clinical research are indicated.

Serum extracellular vesicles contain protein biomarkers for primary sclerosing cholangitis and cholangiocarcinoma

Cholangiocarcinoma (CCA) includes a heterogeneous group of biliary cancers with poor prognosis. Several conditions, such as primary sclerosing cholangitis (PSC), are risk factors. Noninvasive differential diagnosis between intrahepatic CCA and hepatocellular carcinoma (HCC) is sometimes difficult. Accurate noninvasive biomarkers for PSC, CCA, and HCC are not available. In the search for novel biomarkers, serum extracellular vesicles (EV) were isolated from CCA (n = 43), PSC (n = 30), or HCC (n = 29) patients and healthy individuals (control, n = 32); and their protein content was characterized. By using nanoparticle tracking analysis, serum EV concentration was found to be higher in HCC than in all the other groups. Round morphology (by transmission electron microscopy), size (∼180 nm diameter by nanoparticle tracking analysis), and markers (clusters of differentiation 9, 63, and 81 by immunoblot) indicated that most serum EV were exosomes. Proteome profiles (by mass spectrometry) revealed multiple differentially expressed proteins among groups. Several of these proteins showed high diagnostic values with maximum area under the receiver operating characteristic curve of 0.878 for CCA versus control, 0.905 for CCA stage I-II versus control, 0.789 for PSC versus control, 0.806 for noncirhottic PSC versus control, 0.796 for CCA versus PSC, 0.956 for CCA stage I-II versus PSC, 0.904 for HCC versus control, and 0.894 for intrahepatic CCA versus HCC. Proteomic analysis of EV derived from CCA human cells in vitro revealed higher abundance of oncogenic proteins compared to EV released by normal human cholangiocytes. Orthotopic implant of CCA human cells in the liver of immunodeficient mice resulted in the release to serum of EV containing some similar human oncogenic proteins.

CONCLUSION

Proteomic signatures found in serum EV of CCA, PSC, and HCC patients show potential usefulness as diagnostic tools. (Hepatology 2017;66:1125-1143).

Clinical and biological significance of precursor lesions of intrahepatic cholangiocarcinoma

Cholangiocarcinoma (CC) is primarily a malignant tumor of older adults most prevalent in Southeast Asia, where liver fluke infestation is high. However the etiology in western countries is unknown. Although the incidence of extrahepatic cholangiocarcinoma has remained constant, incidence of intrahepatic CC (ICC) which differs in morphology, pathogenesis, risk factors, treatment and prognosis is increasing. While this increase is associated with hepatitis C virus infection, chronic nonalcoholic liver disease, obesity, and smoking, the pathogenesis of ICC and molecular alterations underlying the carcinogenesis are not completely elucidated. Benign biliary lesions such as biliary intraepithelial neoplasia, intraductal papillary neoplasm of the bile duct, von Meyenburg complex or bile duct hamartoma, and bile duct adenoma have been associated with ICC. For each of these entities, evidence suggests or supports a role as premalignant lesions. This article summarized the important biological significance of the precursor lesions of ICC and the molecular mechanisms that may be involved in intrahepatic cholangiocarcinogenesis.

EZH2 is a sensitive marker of malignancy in salivary gland tumors

BACKGROUND

The immunohistochemical detection of Enhancer of zeste homologue 2 (EZH2) proved to be a useful tool to recognize the malignant nature of tumors in a wide variety of neoplasms. The histological diagnostics of salivary gland tumors is a challenging task, and a reliable marker of malignancy would be extremely helpful.

METHODS

EZH2 expression was investigated in 54 malignant and 40 benign salivary gland tumors of various histological types by standard immunohistochemistry.

RESULTS

The majority (n = 52) of the malignant tumors stained positively, while all the investigated benign tumors were negative for EZH2.

CONCLUSIONS

EZH2 expression in salivary gland tumors, similarly to the tumors of other organs is not characteristic for any tumor type, but is a solid marker of the malignant nature of the tumors.

Clinicopathological significance of mucin production in patients with papillary cholangiocarcinoma

BACKGROUND

The clinicopathologic significance of mucin production in patients with papillary cholangiocarcinoma (PCC) is still controversial. We aimed at clarifying the similarities and differences between PCC cases with and without mucin secretion with regard to biological behavior and clinical course.

METHODS

Among 644 patients with surgically resected cholangiocarcinoma (1998-2011), 184 (28 %) patients were considered to have PCC and were enrolled in the study. Those patients were divided into two groups based on whether their PCC was mucin-producing (PCC-M, n = 89) or not (PCC-NM, n = 95). The presence of mucin secretion was determined by the cut surface of the specimens and by pathologic examination.

RESULTS

The clinicopathological features of PCC-M and PCC-NM largely overlapped. No significant between-group differences in malignant potential characteristics, including the depth of invasion, pathological T classification, and regional/periaortic lymph node metastasis, were observed (P = 0.193, 0.181, 0.083, and 0.674, respectively). However, a few clinicopathological differences existed between the two PCC types, i.e., the predominant histological type and epithelial subtype (P < 0.001 and P = 0.016, respectively). Immunohistochemically, MUC2, MUC5AC, MUC6, and HGM were more frequently expressed in PCC-M than PCC-NM (P < 0.002 in all). The disease-specific survival values were not significantly different between the two PCC types (PCC-M; 60 % at 5 year, PCC-NM; 46 %, P = 0.097).

CONCLUSION

PCC-M and PCC-NM were similar in morphology and prognosis. Although a few clinicopathological differences exist between them, their overlapping features and identical survival curves appear to justify the lack of a specific treatment modality for either type.

Involvement of PSMD10, CDK4, and Tumor Suppressors in Development of Intrahepatic Cholangiocarcinoma of Syrian Golden Hamsters Induced by Clonorchis sinensis and N-Nitrosodimethylamine

Background

Clonorchis sinensis is a group-I bio-carcinogen for cholangiocarcinoma (CCA). Although the epidemiological evidence links clonorchiasis and CCA, the underlying molecular mechanism involved in this process is poorly understood. In the present study, we investigated expression of oncogenes and tumor suppressors, including PSMD10, CDK4, p53 and RB in C. sinensis induced hamster CCA model.

Methods

Different histochemical/immunohistochemical techniques were performed to detect CCA in 4 groups of hamsters: uninfected control (Ctrl.), infected with C. sinensis (Cs), ingested N-nitrosodimethylamine (NDMA), and both Cs infected and NDMA introduced (Cs+NDMA). The liver tissues from all groups were analyzed for gene/protein expressions by quantitative PCR (qPCR) and western blotting.

Principal Findings

CCA was observed in all hamsters of Cs+NDMA group with well, moderate, and poorly differentiated types measured in 21.8% ± 1.5%, 13.3% ± 1.3%, and 10.8% ± 1.3% of total tissue section areas respectively. All CCA differentiations progressed in a time dependent manner, starting from the 8^th week of infection. CCA stroma was characterized with increased collagen type I, mucin, and proliferative cell nuclear antigen (PCNA). The qPCR analysis showed PSMD10, CDK4 and p16INK4 were over-expressed, whereas p53 was under-expressed in the Cs+NDMA group. We observed no change in RB1 at mRNA level but found significant down-regulation of RB protein. The apoptosis related genes, BAX and caspase 9 were found downregulated in the CCA tissue. Gene/protein expressions were matched well with the pathological changes of different groups except the NDMA group. Though the hamsters in the NDMA group showed no marked pathological lesions, we observed over-expression of Akt/PKB and p53 genes proposing molecular interplay in this group which might be related to the CCA initiation in this animal model.

Conclusions/Significance

The present findings suggest that oncogenes, PSMD10 and CDK4, and tumor suppressors, p53 and RB, are involved in the carcinogenesis process of C. sinensis induced CCA in hamsters.

Clonorchis sinensis is a helminth parasite and a carcinogenic agent for cholangiocarcinoma (CCA) or bile duct cancer in humans. Though a large and compelling body of evidence suggests an association between C. sinensis and CCA, the mechanism underlying at the genetic/proteomic level is little known. To explore the underlying molecular mechanism we investigated a number of genes/proteins in C. sinensis induced hamster CCA model. Here C. sinensis induced CCA successfully in all hamsters when introduced with N-nitrosodimethylamine. The histopathology confirmed the development of CCA and detected excessive collagen fibers, mucin and cell division related protein. The quantitative PCR analysis showed increased levels of oncogenes PSMD10, CDK4 and decreased level of tumor suppressor gene p53. The western blot analysis observed significant decrease of another tumor suppressor called RB protein. Genes/protein expressions were matched well with the pathological changes of CCA hamster. The present study suggests that oncogenes, PSMD10 and CDK4, and tumor suppressors gene p53 and protein RB, are involved in the carcinogenesis process of C. sinensis induced CCA in hamsters.

Intraductal papillary neoplasms of the bile duct

Intraductal papillary neoplasm of the bile duct (IPNB) is a rare variant of bile duct tumors characterized by papillary growth within the bile duct lumen and is regarded as a biliary counterpart of intraductal papillary mucinous neoplasm of the pancreas. IPNBs display a spectrum of premalignant lesion towards invasive cholangiocarcinoma. The most common radiologic findings for IPNB are bile duct dilatation and intraductal masses. The major treatment of IPNB is surgical resection. Ultrasonography, computed tomography, magnetic resonance image, and cholangiography are usually performed to assess tumor location and extension. Cholangioscopy can confirm the histology and assess the extent of the tumor including superficial spreading along the biliary epithelium. However, pathologic diagnosis by preoperative biopsy cannot always reflect the maximum degree of atypia, because IPNBs are often composed of varying degrees of cytoarchitectural atypia. IPNBs are microscopically classified into four epithelial subtypes, such as pancreatobiliary, intestinal, gastric, and oncocytic types. Most cases of IPNB are IPN with high-grade intraepithelial neoplasia or with an associated invasive carcinoma. The histologic types of invasive lesions are either tubular adenocarcinoma or mucinous carcinoma. Although several authors have investigated molecular genetic changes during the development and progression of IPNB, these are still poorly characterized and controversial.

Intraductal papillary neoplasm of the bile duct

Intraductal papillary neoplasm of the bile duct (IPNB) is a variant of bile duct carcinoma that is characterized by intraductal growth and better outcomes compared with common cholangiocarcinoma. IPNBs are mainly found in patients from Far Eastern areas, where hepatolithiasis and clonorchiasis are endemic. According to the immunohistochemical profiles of the mucin core proteins, IPNBs are classified into four types: pancreaticobiliary, intestinal, gastric, and oncocytic. Approximately 40%-80% of IPNBs contain a component of invasive carcinoma or tubular or mucinous adenocarcinoma, suggesting that IPNB is a disease with high potential for malignancy. It is difficult to make an accurate preoperative diagnosis because of IPNB’s low incidence and the lack of specificity in its clinical manifestation. The most common abnormal preoperative imaging findings of IPNB are intraductal masses and the involvement of bile duct dilation. Simultaneous proximal and distal bile duct dilation can be detected in some cases, which has diagnostic significance. Cholangiography and cholangioscopy are needed to confirm the pathology and demonstrate the extent of the lesions. However, pathologic diagnosis by biopsy cannot reflect the actual stage in many cases because different foci may be of different stages and because mixed pathologic findings may exist in the same lesion. Surgical resection is the major treatment. Systematic cholangioscopy with staged biopsies and frozen sections is recommended during resection to ensure that no minor tumors are left and that curative resection is achieved. Staging, histologic subtype, curative resection and lymph node metastasis are factors affecting long-term survival.

GNAS and KRAS mutations are common in intraductal papillary neoplasms of the bile duct

Intraductal papillary neoplasms of the bile duct (IPNB) shows favorable prognosis and is regarded as a biliary counterpart of intraductal papillary mucinous neoplasm (IPMN) of the pancreas. Although activating point mutations of GNAS at codon 201 have been detected in approximately two thirds of IPMNs of the pancreas, there have been few studies on GNAS mutations in IPNBs. This study investigates the status of GNAS and KRAS mutations and their association with clinicopathological factors in IPNBs. We examined the status of GNAS mutation at codon 201 and KRAS mutation at codon 12&13, degree of mucin production and immunohistochemical expressions of MUC mucin core proteins in 29 patients (M/F = 15/14) with IPNB in intrahepatic and perihilar bile ducts (perihilar IPNB) and 6 patients (M/F = 5/1) with IPNB in distal bile ducts (distal IPNB). GNAS mutations and KRAS mutations were detected in 50% and 46.2% of IPNBs, respectively. There was no significant correlation between the status of GNAS mutation and clinicopathological factors in IPNBs, whereas, the status of KRAS mutation was significantly inversely correlated with the degree of MUC2 expression in IPNBs (p<0.05). All IPNBs with GNAS mutation only showed high-mucin production. Degree of mucin production was significantly higher in perihilar IPNBs than distal IPNBs (p<0.05). MUC2 and MUC5AC expression was significantly higher in IPNBs with high-mucin production than those with low-mucin production (p<0.01 and p<0.05, respectively). In conclusions, this study firstly disclosed frequent GNAS mutations in IPNBs, similarly to IPMNs. This may suggest a common histopathogenesis of IPNBs and IPMNs. The status of KRAS mutations was inversely correlated to MUC2 expression and this may suggest heterogeneous properties of IPNBs. IPNBs with high-mucin production are characterized by perihilar location and high expression of MUC2 and MUC5AC, irrespective of the status of GNAS and KRAS mutations.