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Objective: The aim of this study was to define robust benchmark values for the surgical treatment of perihilar cholangiocarcinomas (PHC) to enable unbiased comparisons., Background: Despite ongoing efforts, postoperative mortality and morbidity remains high after complex liver surgery for PHC. Benchmark data of best achievable results in surgical PHC treatment are however still lacking., Methods: This study analyzed consecutive patients undergoing major liver surgery for PHC in 24 high-volume centers in 3 continents over the recent 5-year period (2014-2018) with a minimum follow-up of 1 year in each patient. Benchmark patients were those operated at high-volume centers (≥50 cases during the study period) without the need for vascular reconstruction due to tumor invasion, or the presence of significant co-morbidities such as severe obesity (body mass index ≥35), diabetes, or cardiovascular diseases. Benchmark cutoff values were derived from the 75th or 25th percentile of the median values of all benchmark centers., Results: Seven hundred eight (39%) of a total of 1829 consecutive patients qualified as benchmark cases. Benchmark cut-offs included: R0 resection ≥57%, postoperative liver failure (International Study Group of Liver Surgery): ≤35%; in-hospital and 3-month mortality rates ≤8% and ≤13%, respectively; 3-month grade 3 complications and the CCI: ≤70% and ≤30.5, respectively; bile leak-rate: ≤47% and 5-year overall survival of ≥39.7%. Centers operating mostly on complex cases disclosed better outcome including lower post-operative liver failure rates (4% vs 13%; P = 0.002). Centers from Asia disclosed better outcomes., Conclusion: Surgery for PHC remains associated with high morbidity and mortality with now the availability of benchmark values covering 21 outcome parameters, which may serve as key references for comparison in any future analyses of individuals, group of patients or centers., Competing Interests: The authors report no conflicts of interest., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Background: Misclassification of Klatskin tumor as intrahepatic rather than extrahepatic bile duct cancer (eBDC) may overestimate the incidence of intrahepatic BDC (iBDC). This study aimed to investigate the impact of misclassified Klatskin tumor on iBDC and eBDC incidences in Korea, where BDC is highly endemic., Methods: The data of incidence, topography and morphology code of BDC from 1999 to 2017 were obtained from the Korea Central Cancer Registry, which covers the entire 51.6 million Korean population. For misclassification analysis, all Klatskin tumors were reclassified as eBDC., Results: Klatskin tumors accounted for 13.5% of all 81 414 BDC cases. In the registry, an average of 59.7% of Klatskin tumors were classified as iBDC, gradually decreasing from 95.5% to 16.9%. Misclassification led to a 17.3% overestimation of iBDC cases and a 15.0% underestimation of eBDC cases on average. After reclassification, age standardized rate (ASR) of incidence per 100 000 population decreased in iBDC from 3.4 to 2.9 and increased in eBDC from 2.8 to 3.2. Average annual percentage change of iBDC and eBDC incidences were 2.0% and 1.2%, respectively, but ASR of iBDC significantly decreased since 2012 (P < 0.0001)., Conclusions: Misclassification of Klatskin tumors has remarkable impact on the incidence of iBDC and eBDC in a highly endemic country., (© 2021 Japanese Society of Hepato-Biliary-Pancreatic Surgery.)

Introduction: Cholangiocarcinoma (CCA) are sub-divided into intrahepatic (iCCA) or extrahepatic (eCCA). eCCA are further subdivided into perihilar (pCCA) and distal (dCCA). Current and previous versions of the WHO International Coding of Disease and Oncology classifications (ICD) have separate topography codes for iCCA and eCCA, but none for pCCA. Over recent decades, multiple studies report rising incidence rates of iCCA with declining rates of eCCA, without reference to pCCA. We hypothesised the lack of a specific code for pCCA has led to errors CCA coding, specifically with miscoding of pCCA as iCCA., Methods: Clinical notes of cases coded as hepatobiliary carcinoma using ICD-10 criteria (C22.1/Intrahepatic Bile Duct carcinoma, C24.0/Extrahepatic Bile Duct carcinoma, C23X/Malignant Neoplasm Gall Bladder, C22.0/Malignant Neoplasm Liver Cell Carcinoma) over a 2 year period (2015-2017), were reviewed by two independent clinicians at three independent UK regional HepatoPancreatoBiliary centres. The agreed final diagnosis was compared to the originally allocated ICD-10 code., Results: Of the 625 CCA cases fully reviewed, 226 were coded as C22.1/iCCA. 98 (43%) of these were true iCCA and coded correctly, while 76 cases (34%) were actually pCCA. 92% all pCCA cases were incorrectly coded as iCCA., Conclusion: CCA coding misclassification in UK HPB centres is common, particularly the miscoding of pCCA, which is extrahepatic and the commonest form of CCA, as iCCA. This may be contributing to apparent rising incidence rates of iCCA. Our findings confirm the need to implement distinct topographical codes for iCCA, pCCA and dCCA in future iterations of ICD., (Copyright © 2020 Elsevier Ltd, BASO ~ The Association for Cancer Surgery, and the European Society of Surgical Oncology. All rights reserved.)

BACKGROUND Klatskin tumor (KCC) is a rare type of tumor, with an annual incidence rate of no more than 1: 100 000. Because of its rarity, KCC is difficult to investigate. The present study provides new insights into KCC by a using public database. MATERIAL AND METHODS We used the Surveillance, Epidemiology, and End Results (SEER) database to conduct the analysis. Klatskin tumor patients were identified and compared with patients that had other kinds of cholangiocarcinomas (OCC). We identified differences between the 2 groups of patients and assessed tumor characteristics. We used Cox regression analysis to identify the prognostic indicators for KCC. The propensity score 1-to-1 matching method was used to compare the survival difference between KCC and OCC. RESULTS We extracted data on 26 137 patients diagnosed with cholangiocarcinomas between 1973 and 2014 from the SEER database: 1341 cases were diagnosed with KCC and 24 796 cases were diagnosed with OCC. The number of diagnoses has gradually increased in both groups. There were significant differences in pathology grades, T stage, N stage, M stage, and SEER historic stage between the KCC and OCC groups. Survival analysis showed that the OCC group had better survival compared to the KCC group, both in matched and unmatched cohorts. The Cox regression results showed that older age, higher M stages, and higher pathology grades were associated with worse prognosis for KCC patients. CONCLUSIONS KCC patients have worse survival compared to OCC patients. Older age, higher M stages, and higher pathology grades were associated with worse survival in KCC patients.

Objectives: The objective of this study was to investigate the differences between cholangiocarcinoma (CC) subtypes in terms of incidence rate, clinical presentation, management and survival by applying a stable anatomical classification in a population-based study., Patients and Methods: Cancer data for the period 2000-2012 were obtained from a specialized digestive cancer registry in the Department of Calvados, France. Patients' files were checked, and the diagnosis was verified by two hepatobiliary surgeons. This approach prevents classifying perihilar cholangiocarcinoma (PHCC) as intrahepatic cholangiocarcinoma (ICC), thereby allowing an accurate estimation of their respective epidemiological characteristics., Results: A total of 320 patients with CC were included. ICC represented 41% (130), whereas PHCC and distal cholangiocarcinoma represented 36 (116) and 23% (74), respectively. The mean age at the time of diagnosis differed significantly between the three subtypes (P<0.05). ICC was discovered accidently more frequently than PHCC, which was associated significantly with clinical symptoms. No change in the incidence or survival rates of CC subtypes were noticed, except for PHCC, in which female individuals had a significantly shorter median and 5-year survival rate of 0% (P<0.05)., Conclusion: The frequency of PHCC is overestimated in the literature. The anatomical reclassification of CC subtypes shows the stability of their incidence and survival rates. Considering ICC and PHCC as two different entities implies the need to assign a specific topographic code for PHCC.

To evaluate the prognostic value of numbers of negative lymph nodes (NLNs) for patients with perihilar cholangiocarcinomas.The surveillance, epidemiology, and end results database was used to screen for patients with perihilar cholangiocarcinomas. Kaplan-Meier and Cox regression analyses were used for statistical evaluations. Subsequently, propensity score matching (PSM) was performed to confirm the results.A total of 938 patients with perihilar cholangiocarcinomas met the inclusion criteria. The cut-off number for the grouping of patients with different numbers of NLNs was 17. Both the univariate and multivariate survival analyses demonstrated that there was a significant improvement in terms of cancer-specific survival for patients with >17 NLNs, compared with patients with ≤17 NLNs. Then, the above results were confirmed via a PSM procedure. Additionally, the independent prognostic value of NLNs was evaluated in subgroup univariate and multivariate analyses of patients with stage I or stage II tumors.The numbers of NLNs were evaluated and determined to be important independent prognostic factors for the cancer-specific survival of patients with perihilar cholangiocarcinomas.

Surgical site infection (SSI) is one of the major morbidities after radical resection for perihilar cholangiocarcinoma (PHCC). This study aimed to clarify the risk factors and construct a nomogram to predict SSIs in patients with PHCC.A total of 335 consecutive patients who underwent hepatectomy combined with hepaticojejunostomy between January 2013 and December 2015 were analyzed retrospectively. SSIs, including incisional (superficial and deep) and space/organ infection, were defined according to the Centers for Disease Control and Prevention (CDC)'s National Nosocomial Infection Surveillance (NNIS) system. Risk factors associated with postoperative SSIs were analyzed by univariate and multivariate analyses. A nomogram was developed on the basis of results from the multivariate logistic model and the discriminatory ability of the model was analyzed.PHCC patients had higher organ/space SSI rate than incisional SSI rate after radical resection. Multivariate analysis showed that risk factors indicating postoperative overall SSIs (incisional and organ/space) included coexisting cholangiolithiasis [odds ratio (OR): 6.77; 95% confidence interval (95% CI): 2.40-19.11; P < .001], blood loss >1500 mL (OR: 4.77; 95% CI: 1.45-15.65; P  =  .010), having abdominal surgical history (OR: 5.85; 95% CI: 1.91-17.97; P  =  .002), and bile leakage (OR: 15.28; 95% CI: 5.90-39.62; P < .001). The β coefficients from the multivariate logistic model were used to construct the model for estimation of SSI risk. The scoring model was as follows: -4.12 +1.91 × (coexisting cholangiolithiasis  =  1) + 1.77 × (having previous abdominal surgical history  =  1) +1.56 × (blood loss >1500 mL  =  1) + 2.73 × (bile leakage  =  1). The discriminatory ability of the model was good and the area under the receiver operating characteristic (ROC) curve (AUC) was 0.851.In PHCC patients, there may be a relationship between postoperative SSIs and abdominal surgical history, coexisting cholangiolithiasis, bile leakage, and blood loss. The nomogram can be used to estimate the risk of postoperative SSIs in patients with PHCC.

Cholangiocarcinoma (CCA) is the second most common primary malignancy. Although it is more common in Asia, its incidence in Europe and North America has significantly increased in recent decades. The prognosis of CCA is dismal. Surgery is the only potentially curative treatment, but the majority of patients present with advanced stage disease, and recurrence after resection is common. Over the last two decades, our understanding of the molecular biology of this malignancy has increased tremendously, diagnostic techniques have evolved, and novel therapeutic approaches have been established. This review discusses the changing epidemiologic trends and provides an overview of newly identified etiologic risk factors for CCA. Furthermore, the molecular pathogenesis is discussed as well as the influence of etiology and biliary location on the mutational landscape of CCA. This review provides an overview of the diagnostic evaluation of CCA and its staging systems. Finally, new therapeutic options are critically reviewed, and future therapeutic strategies discussed.

An American Hepato-Pancreato-Biliary Association (AHPBA)-sponsored consensus meeting of expert panellists met on 15 January 2014 to review current evidence on the management of hilar cholangiocarcinoma in order to establish practice guidelines and to agree consensus statements. It was established that the treatment of patients with hilar cholangiocarcinoma requires a coordinated, multidisciplinary approach to optimize the chances for both durable survival and effective palliation. An adequate diagnostic and staging work-up includes high-quality cross-sectional imaging; however, pathologic confirmation is not required prior to resection or initiation of a liver transplant trimodal treatment protocol. The ideal treatment for suitable patients with resectable hilar malignancy is resection of the intra- and extrahepatic bile ducts, as well as resection of the involved ipsilateral liver. Preoperative biliary drainage is best achieved with percutaneous transhepatic approaches and may be indicated for patients with cholangitis, malnutrition or hepatic insufficiency. Portal vein embolization is a safe and effective strategy for increasing the future liver remnant (FLR) and is particularly useful for patients with an FLR of <30%. Selected patients with unresectable hilar cholangiocarcinoma should be evaluated for a standard trimodal protocol incorporating external beam and endoluminal radiation therapy, systemic chemotherapy and liver transplantation. Post-resection chemoradiation should be offered to patients who show high-risk features on surgical pathology. Chemoradiation is also recommended for patients with locally advanced, unresectable hilar cancers. For patients with locally recurrent or metastatic hilar cholangiocarcinoma, first-line chemotherapy with gemcitabine and cisplatin is recommended based on multiple Phase II trials and a large randomized controlled trial including a heterogeneous population of patients with biliary cancers., (© 2015 International Hepato-Pancreato-Biliary Association.)

Background & Aims: Perihilar cholangiocarcinoma (pCCA) is the most common form of bile duct cancer, arising from cholangiocytes at the confluence of hepatic ducts. Given the diversity of cholangiocarcinoma (CCA) aetiology according to the location, and the scarcity of studies on the aetiology of pCCA, we aimed to identify the risk factors for pCCA., Methods: A total of 81 patients diagnosed with pCCA between July 2007 and December 2013, and 162 controls matched 2:1 for age, sex and date of diagnosis were included in this hospital-based case-control study. Potential risk factors were retrospectively investigated through clinical records, and the associations with pCCA were studied by calculating the odds ratios (ORs) using conditional logistic regression analysis., Results: In the univariate model, the prevalence of choledocholithiasis (OR: 14.00, P = 0.014), hepatolithiasis (OR: 12.00, P = 0.021) and diabetes mellitus (DM) (OR: 2.74, P = 0.005) was higher in pCCA patients than in controls. Heavy smoking and cirrhosis were marginally significant risk factors for pCCA (P < 0.1). Multivariate analysis revealed an association between pCCA and hepatolithiasis, choledocholithiasis, DM, and heavy smoking, each, with adjusted ORs of 16.47, 9.39, 3.36 and 2.52 respectively. DM, heavy smoking, hepatolithiasis and choledocholithiasis accounted for about 22.5%, 17.1%, 8.5% and 4.8% of pCCA risk respectively (population attributable risk percentage)., Conclusion: Our data showed that DM, heavy smoking, choledocholithiasis and hepatolithiasis were risk factors for pCCA development, implying that pCCA may share some aetiological factors with intrahepatic CCA although it has been classified as extrahepatic CCA., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Hilar cholangiocarcinoma (HCC) remains one of the most difficult tumors to stage and treat. The aim of the study was to assess the diagnostic efficiency of computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography/computer tomography (PET/CT) in evaluating the resectability of HCC. A systematic search was performed of the PubMed, EMBASE, and Cochrane databases. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy were calculated for individual studies and pooled data as well as test for heterogeneity and public bias. Our data showed that CT had the highest pooled sensitivity at 95% (95% CI: 91-97), whereas PET/CT had the highest pooled specificity at 81% (95% CI: 69-90). The area under the curve (AUC) of CT, MRI, and PET/CT was 0.9269, 0.9194, and 0.9218, respectively. In conclusion, CT is the most frequently used imaging modality to assess HCC resectability with a good sensitivity and specificity. MRI was generally comparable with that of CT and can be used as an alternative imaging technique. PET/CT appears to be the best technique in detecting lymph node and distant metastasis in HCC but has no clear role in helping to evaluate issues of local resectability.

Background and Aims: It has been reported that the incidence of intrahepatic cholangiocarcinoma (ICC) has increased in the USA, while extrahepatic cholangiocarcinoma (ECC) has decreased or remained stable. However, neither the recent trends nor the effects of the misclassification of Klatskin tumors are known., Methods: Using the Surveillance, Epidemiology, and End Results program databases, we calculated the average annual age-adjusted incidence rates (AA-IRs) of ICC and ECC in 4-year time periods (1992-1995, 1996-1999, 2000-2003, 2004-2007). These AA-IRs were calculated with misclassified as well as correctly classified Klatskin tumors. AA-IRs were also calculated based on age, sex, and race. Multivariable Poisson regression models were used to evaluate the secular trends of ICC and ECC., Results: The AA-IR of ICC was 0.92 in 1992-1995 and 0.93 in 2004-2007, while the AA-IR of ECC increased from 0.70 in 1992-1995 to 0.95 in 2004-2007. There was no significant trend in AA-IR of ICC (p = 0.07), while there was a significant increase in ECC across the 4-year time periods (p < 0.001). Klatskin tumors comprised 6.7% of CCs with approximately 90 and 45% misclassified as ICC during 1992-2000 and 2001-2007, respectively. Adjusted Poisson models showed no significant differences in the temporal trend of ICC or ECC due to misclassification of Klatskin tumors., Conclusions: The incidence of ICC has remained stable between 1992 and 2007 with only slight fluctuations, while the incidence of ECC has been increasing. Misclassification of Klatskin tumors does not appear to play a significant role in the trends of CCs.

Hilar cholangiocarcinoma (HCCA) is one of the most common types of hepatobiliary cancers reported in the world including Asia-Pacific region. Early HCCA may be completely asymptomatic. When significant hilar obstruction develops, the patient presents with jaundice, pale stools, dark urine, pruritus, abdominal pain, and sometimes fever. Because no single test can establish the definite diagnosis then, a combination of many investigations such as tumor markers, tissue acquisition, computed tomography scan, magnetic resonance imaging/magnetic resonance cholangiopancreatography, endoscopic ultrasonography/intraductal ultrasonography, and advanced cholangioscopy is required. Surgery is the only curative treatment. Unfortunately, the majority of HCCA has a poor prognosis due to their advanced stage on presentation. Although there is no survival advantage, inoperable HCCA managed by palliative drainage may benefit from symptomatic improvement. Currently, there are three techniques of biliary drainage which include endoscopic, percutaneous, and surgical approaches. For nonsurgical approaches, stent is the most preferred device and there are two types of stents i.e. plastic and metal. Type of stent and number of stent for HCCA biliary drainage are subjected to debate because the decision is made under many grounds i.e. volume of liver drainage, life expectancy, expertise of the facility, etc. Recently, radio-frequency ablation and photodynamic therapy are promising techniques that may extend drainage patency. Through a review in the literature and regional data, the Asia-Pacific Working Group for hepatobiliary cancers has developed statements to assist clinicians in diagnosing and managing of HCCA. After voting anonymously using modified Delphi method, all final statements were determined for the level of evidence quality and strength of recommendation., (© 2013 Journal of Gastroenterology and Hepatology Foundation and Wiley Publishing Asia Pty Ltd.)

Background & Aims: Cholangiocarcinomas (CC) can be sub-divided into intrahepatic (IHCC) or extrahepatic (EHCC). Hilar or 'Klatskin' tumours are anatomically extrahepatic. Most international studies, also from the UK, report increasing IHCC and decreasing EHCC incidence. The second edition of the International Classification of Diseases for Oncology (ICD-O-2) assigned 'Klatskin' tumours a unique histology code (8162/3), but this was cross-referenced to the topography code for intrahepatic (IHBD) rather than extrahepatic bile duct tumours (EHBD). Under the third ICD-O edition, 'Klatskin' tumours are cross-referenced to either IHBD or EHBD. New editions of the ICD-O classification are adopted at different time points by different countries. We investigated the impact of changing ICD-O classifications and the potential misclassification of hilar/'Klatskin' tumours on bile duct tumour and CC incidence rates in England and Wales and the US. We also examined whether coding practices by cancer registries in England and Wales could be influencing these rates., Methods: We analysed age-standardised incidence rates (ASIR) in England and Wales for IHBD and EHBD tumours between 1990 and 2008, then transferred all 'Klatskin' tumours from IHBD to EHBD and reanalysed rates from 1995, when ICD-O-2 was introduced in the UK. We also compared trends in IHBD, EHBD, and 'Klatskin' tumours in England and Wales with those in the USSEER (Surveillance, Epidemiology and End Results) database. Coding practice at Cancer registry level in England and Wales was investigated via a questionnaire completed by all national cancer registries., Results: In England and Wales, 1990-2008, ASIR of IHBD cancers rose (0.43-1.84/100,000 population in males; 0.27-1.51 in females) but fell for EHBD (0.78-0.51/100,000 population in males; 0.62-0.39 in females). After transferring all 'Klatskin' tumours from IHBD to EHBD, there remained a marked increase in ASIR of IHBD cancers and a decrease in ASIR for EHBD, as only 1% of CC were reportedly 'Klatskin'. The US SEER data showed that ASIR for IHBD gradually rose from 0.59/100,000 population in 1990 to 0.91 in 2001, then sharply fell before plateauing at 0.60 by 2007. ASIR for EHBD remained relatively stable at around 0.80/100,000 population until 2001, then began increasing, to 0.97 by 2007. Annually, between 1995 and 2008, the vast majority of 'Klatskin' tumours in England and Wales were coded as IHBD. This was also the case in the SEER data until 2001, when the situation was reversed and subsequently most 'Klatskin' tumours were coded as EHBD. US trends coincide with a switch from ICD-O2 to ICD-O-3 in 2001. In the UK, the switch to ICD-O-3 only occurred in 2008. On questioning, cancer registries in England and Wales stated they would not code a CC described as 'hilar' with the designated 'Klatskin' histology code. If the tumour site is unspecified, most registries classify CC as intrahepatic., Conclusions: Changes in ICD-classification may be influencing observed changes in IHBD and EHBD incidence rates. Coding misclassification is likely to have been skewing CC registration to an intrahepatic site, thereby contributing to the previously reported rise in intrahepatic tumours., (Copyright © 2011 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)

Background: The term "cholangiocarcinoma" was originally used only for intrahepatic bile duct (adeno)carcinomas, but is now regarded as inclusive of intrahepatic, perihilar, and distal extrahepatic tumors of the bile ducts. A rise in incidence of intrahepatic cholangiocarcinoma has been recently reported in Western countries but comparatively little is known about recent cholangiocarcinoma incidence trends in East and South-Eastern Asia., Methods: We compared age-adjusted incidence rates of both intrahepatic and extrahepatic cholangiocarcinomas, as well as coding practices, using data from 18 cancer registries in Asia and 4 selected registries in Western countries. Intrahepatic cholangiocarcinoma incidence rates were calculated after reallocation of cases with unknown or unspecified histology among liver cancer cases., Results: Age-adjusted incidence rates of intrahepatic cholangiocarcinoma varied by more than 60-fold by region. The highest rates were found in Khon Kaen, Thailand, where 90% of liver tumors were cholangiocarcinomas. The next highest rates were found in the People's Republic of China, followed by the Republic of Korea. The highest age-adjusted incidence rate for extrahepatic cholangiocarcinoma was found in Korea. Coding practices for perihilar (Klatskin tumor) or unspecified sites of cholangiocarcinoma differed from one cancer registry to the other. The proportion of Klatskin tumors among cholangiocarcinomas was less than the one reported in clinical settings., Conclusion: Developing a consistent and uniform topographical classification for acceptable coding practice to all health professionals is necessary. In addition, epidemiological research on risk factors according to anatomical location (intrahepatic versus extrahepatic) and the macroscopic appearance and/or new histological classification of cholangiocarcinoma is also needed.

Due to their anatomical position, the tendency of early infiltrative growth and their poor prognosis without treatment, klatskin tumors are challenging concerning diagnosis and therapy. In contrast to other tumors of the gastrointestinal tract, for which exact diagnostic and stage dependent therapeutic guidelines could be formulated, clear recommendations for klatskin tumors are missing. Thus, survival rates after local resection, e. g. resection of the bile duct bifurcation alone, show high rates of R1/2 resection and early tumor recurrence. With an additional hepatic resection formally curative resections and long-term survival can be improved. Extended liver resections including the portal vein provide the highest rates of R0 resections for hilar carcinomas of the extrahepatic bile duct. Survival rates after liver transplantation for klatskin tumors are not yet convincing. Promising first results have been reported for the combination of neoadjuvant treatment and liver transplantation and might show future perspectives for the treatment of klatskin tumors.

Cholangiocarcinomas are topographically categorized as intrahepatic or extrahepatic by the International Classification of Diseases for Oncology (ICD-O). Although hilar cholangiocarcinomas (Klatskin tumors) are extrahepatic cholangiocarcinomas, the second edition of the ICD-O (ICD-O-2) assigned them a histology code 8162/3, Klatskin, which was cross-referenced to intrahepatic cholangiocarcinoma. Recent studies in the United States that included this code (8162/3, Klatskin) with intrahepatic cholangiocarcinoma reported an increasing incidence of intrahepatic cholangiocarcinoma and a decreasing incidence of extrahepatic cholangiocarcinoma. To investigate the impact of this misclassification on site-specific cholangiocarcinoma incidence rates, we calculated annual percent changes (APCs) with data from the Surveillance, Epidemiology, and End Results (SEER) program using a Poisson regression model that was age-adjusted to the year 2000 U.S. population. All statistical tests were two-sided. During 1992-2000, when SEER used ICD-O-2, 1710 intrahepatic cholangiocarcinomas, 1371 extrahepatic cholangiocarcinomas, and 269 hilar cholangiocarcinomas identified by code 8162/3, Klatskin were diagnosed. Ninety-one percent (246 of 269) of the hilar cholangiocarcinomas were incorrectly coded as intrahepatic cholangiocarcinomas, resulting in an overestimation of intrahepatic cholangiocarcinoma incidence by 13% and underestimation of extrahepatic cholangiocarcinomas incidence by 15%. However, even after the exclusion of tumors that were coded to the histology code 8162/3, Klatskin, age-adjusted annual intrahepatic cholangiocarcinoma incidence increased during this period (APC = 4%, 95% confidence interval = 2% to 6%, P<.001).