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Modification of the AJCC/UICC 8th edition staging system for intrahepatic cholangiocarcinoma: proposal for an alternative staging system from cholangiocarcinoma-prevalent Northeast Thailand

  • Prakasit Sa-Ngiamwibool
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Chaiwat Aphivatanasiri
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Sakkarn Sangkhamanon
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Piyapharom Intarawichian
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Waritta Kunprom
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Malinee Thanee
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Piya Prajumwongs
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Watcharin Loilome
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Biochemistry, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Narong Khuntikeo
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Surgery, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Attapol Titapun
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Surgery, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Apiwat Jareanrat
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Surgery, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Vasin Thanasukarn
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Surgery, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Tharatip Srisuk
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Surgery, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Vor Luvira
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Surgery, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Kulyada Eurboonyanun
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Radiology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Julaluck Promsorn
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Radiology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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  • Aileen Wee
    Affiliations
    Department of Pathology, National University Hospital, Singapore
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  • Supinda Koonmee
    Correspondence
    Correspondence: Supinda Koonmee, Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand.
    Affiliations
    Cholangiocarcinoma Screening and Care Program (CASCAP), Khon Kaen University, Khon Kaen, Thailand

    Cholangiocarcinoma Research Institute, Khon Kaen University, Khon Kaen, Thailand

    Department of Pathology, Faculty of Medicine, Khon Kaen University, Khon Kaen, Thailand
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Open AccessPublished:June 20, 2022DOI:https://doi.org/10.1016/j.hpb.2022.06.004

      Abstract

      Background

      Intrahepatic cholangiocarcinoma (iCCA) arises from bile ducts within the liver. Thailand has the highest incidence of CCA worldwide, with a high mortality rate. Early diagnosis and accurate prognostic stratification can improve overall survival. We aim to modify the AJCC/UICC 8th edition staging system for iCCA by creating the Khon Kaen University (KKU) staging system for more precise patient stratification and prognostic prediction.

      Methods

      A total of 298 iCCA patients who underwent hepatectomy were included in this retrospective study at the Srinagarind Hospital, Khon Kaen University, Thailand. Univariate and multivariate analysis were performed to examine survival rate, hazard ratio, and prognostic factors.

      Results

      Univariate and multivariate analysis of the cohort showed that growth patterns, histological type, histological grade, lymph node metastasis and distant metastasis were independent prognostic factors when compared to the respective reference groups. The 8th AJCC staging system incorporated growth patterns into the KKU staging system. This model modified AJCC stages I, II, and III for better prediction of patient survival.

      Conclusion

      Growth patterns were incorporated to improve the 8th AJCC staging system for prognostication of iCCA patients in Northeast Thailand. We propose the KKU staging system as an alternative model for iCCA staging to augment the accuracy of survival prognostication.

      Graphical abstract

      Introduction

      Cholangiocarcinoma (CCA) may originate in the intra- or extrahepatic biliary tree.
      • Bhudhisawasdi V.
      • Khuntikeo N.
      • Chur-in S.
      • Pugkhem A.
      • Talabnin C.
      • Wongkham S.
      Cholangiocarcinoma: experience of Srinagarind hospital.
      Epidemiological studies show that CCA is rare in most countries (age-standardized incidence of <6 per 100,000 population). However, the incidence is exceptionally high in Asian countries like China, Korea, Japan, and Thailand. The northeastern region of Thailand has the highest incidence worldwide (85 per 100,000 population per year).
      • Banales J.M.
      • Cardinale V.
      • Carpino G.
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      Expert consensus document: cholangiocarcinoma: current knowledge and future perspectives consensus statement from the European Network for the Study of Cholangiocarcinoma (ENS-CCA).
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      The global burden of cancer 2013.
      • Sripa B.
      • Pairojkul C.
      Cholangiocarcinoma: lessons from Thailand.
      This high incidence is due to infestation by the liver fluke, Opisthorchis viverrini (OV.) - a significant risk factor for CCA by way of several carcinogenic mechanisms that can enhance cholangiocarcinogenesis.
      • Sripa B.
      • Pairojkul C.
      Cholangiocarcinoma: lessons from Thailand.
      Studies have consistently documented that OV. infestation is associated with cholangiocarcinogenesis in Thai patients, also known as OV.-associated CCA.
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      • Mairiang P.
      • Sithithaworn P.
      • Kaewkes S.
      • et al.
      A high frequency of hepatobiliary disease and suspected cholangiocarcinoma associated with heavy Opisthorchis viverrini infection in a small community in north-east Thailand.
      • Mairiang E.
      • Elkins D.B.
      • Mairiang P.
      • Chaiyakum J.
      • Chamadol N.
      • Loapaiboon V.
      • et al.
      Relationship between intensity of Opisthorchis viverrini infection and hepatobiliary disease detected by ultrasonography.
      • Haswell-Elkins M.R.
      • Satarug S.
      • Tsuda M.
      • Mairiang E.
      • Esumi H.
      • Sithithaworn P.
      • et al.
      Liver fluke infection and cholangiocarcinoma: model of endogenous nitric oxide and extragastric nitrosation in human carcinogenesis.
      • Honjo S.
      • Srivatanakul P.
      • Sriplung H.
      • Kikukawa H.
      • Hanai S.
      • Uchida K.
      • et al.
      Genetic and environmental determinants of risk for cholangiocarcinoma via Opisthorchis viverrini in a densely infested area in Nakhon Phanom, northeast Thailand.
      • Sriamporn S.
      • Pisani P.
      • Pipitgool V.
      • Suwanrungruang K.
      • Kamsa-ard S.
      • Parkin D.M.
      Prevalence of Opisthorchis viverrini infection and incidence of cholangiocarcinoma in Khon kaen, northeast Thailand.
      CCA has a high mortality rate due to difficulties in early diagnosis, resulting in metastatic disease at presentation.
      • Sirica A.E.
      Cholangiocarcinoma: molecular targeting strategies for chemoprevention and therapy.
      Accurate stratification and staging of CCA patients are essential for counseling, predicting prognosis, and guiding treatment options.
      The classification of CCA is based on anatomical localization and comprises intrahepatic (iCCA), perihilar (pCCA), and distal CCA (dCCA). Although all are similar, there are some important inter-and intra-tumoral differences that can affect pathogenesis and outcome. A progressive increase in worldwide iCCA incidence was reported up to the end of the last century, reaching a plateau in the past ten years. By contrast, the incidences of both pCCA and dCCA appear to be decreasing.
      • Fitzmaurice C.
      • Dicker D.
      • Pain A.
      • Hamavid H.
      • Moradi-Lakeh M.
      • MacIntyre M.F.
      • et al.
      The global burden of cancer 2013.
      This study focuses on iCCA because of increased incidence and high mortality rates due to its biological nature of early invasion, high recurrence, and widespread metastasis, coupled with lack of effective treatment.
      • Khan S.A.
      • Taylor-Robinson S.D.
      • Toledano M.B.
      • Beck A.
      • Elliott P.
      • Thomas H.C.
      Changing international trends in mortality rates for liver, biliary and pancreatic tumours.
      Intrahepatic CCA can be further subclassified based on growth patterns according to the Liver Cancer Study Group of Japan (LCSGJ).
      • Yamasaki S.
      Intrahepatic cholangiocarcinoma: macroscopic type and stage classification.
      The patterns are mass-forming (MF), periductal-infiltrating (PI), intraductal (ID), and mixed types, all of which have prognostic implications.
      • Yamasaki S.
      Intrahepatic cholangiocarcinoma: macroscopic type and stage classification.
      • Aishima S.
      • Oda Y.
      Pathogenesis and classification of intrahepatic cholangiocarcinoma: different characters of perihilar large duct type versus peripheral small duct type.
      • Dodson R.M.
      • Weiss M.J.
      • Cosgrove D.
      • Herman J.M.
      • Kamel I.
      • Anders R.
      • et al.
      Intrahepatic cholangiocarcinoma: management options and emerging therapies.
      • Razumilava N.
      • Gores G.J.
      Suzuki et al. showed that MF growth pattern is related to short survival of iCCA patients, and hepatectomy for MF is an appropriate surgical treatment that can prolong survival approximately three folds [median survival time = 6 months for unresectable iCCA and 18 months for resectable iCCA]. Moreover, 7 out of the 19 cases reported have associated MF with PI; this mixed pattern has shorter survival rate than MF alone.
      • Suzuki S.
      • Sakaguchi T.
      • Yokoi Y.
      • Okamoto K.
      • Kurachi K.
      • Tsuchiya Y.
      • et al.
      Clinicopathological prognostic factors and impact of surgical treatment of mass-forming intrahepatic cholangiocarcinoma.
      This observation was corroborated by Shimada et al.
      • Shimada K.
      • Sano T.
      • Sakamoto Y.
      • Esaki M.
      • Kosuge T.
      • Ojima H.
      Surgical outcomes of the mass-forming plus periductal infiltrating types of intrahepatic cholangiocarcinoma: a comparative study with the typical mass-forming type of intrahepatic cholangiocarcinoma.
      In Thailand, the consistently poor outcome of MF and PI compared to ID pattern was found in a study cohort in Srinagarind Hospital by Bhudhisawasdi et al.
      • Bhudhisawasdi V.
      • Khuntikeo N.
      • Chur-in S.
      • Pugkhem A.
      • Talabnin C.
      • Wongkham S.
      Cholangiocarcinoma: experience of Srinagarind hospital.
      Tawarungruang et al. studied the impact of growth patterns on iCCA, pCCA, and dCCA in 746 Thai CCA patients. Results showed that in all types of CCA, MF and PI had significantly shorter survival times than ID.
      • Tawarungruang C.
      • Khuntikeo N.
      • Chamadol N.
      • Laopaiboon V.
      • Thuanman J.
      • Thinkhamrop K.
      • et al.
      Survival after surgery among patients with cholangiocarcinoma in Northeast Thailand according to anatomical and morphological classification.
      Therefore, growth patterns should be considered an important additional factor for the stratification of iCCA patients.
      The emerging importance of iCCA has been recognized by the American Joint Committee on Cancer (AJCC), and a new separate staging system for iCCA has been included in the most recent 8th edition of the AJCC Cancer Staging Manual.
      • Amin M.B.
      • Edge S.B.
      • Greene F.L.
      • Byrd D.R.
      • Byrd R.K.
      • Washington M.K.
      • et al.
      AJCC cancer staging manual.
      ,
      • Lee A.J.
      • Chun Y.S.
      Intrahepatic cholangiocarcinoma: the AJCC/UICC 8th edition updates.
      Nowadays, the AJCC 8th edition staging system is used as a guideline for predicting pathological staging of iCCA. Tumor size, lymphovascular invasion, lymph node metastasis, and distant metastasis provide precise stratification of disease extent in the majority of patients. However, it has been observed that some patients have survival durations not correlated with their respective 8th AJCC TNM stage; they were apparently under-staged, resulting in under-management with consequent poor survival. There is, thus, a need for refinement of the current T categories to enable up- or downstaging of patients who have had survival durations not in keeping with the 8th AJCC staging system. Additional factors such as growth patterns, histological type, and histological grade have been recommended, but they have yet to be implemented.
      In this study, we propose the Khon Kaen University (KKU) staging system by modifying the 8th AJCC staging system with the incorporation of additional factor/s to improve pathological staging and prognostic stratification of iCCA patients.

      Methods

      Patients

      Between 2002 and 2017, 343 patients were diagnosed with iCCA at the Srinagarind Hospital, Faculty of Medicine, Khon Kaen University, Thailand. Patients with liver biopsies only or wedge resections (n = 32), those who survived less than 30 days after surgery with likely perioperative causes of death (n = 10), and combined hepatocellular-cholangiocarcinoma (cHCC-CCA, n = 3) were excluded. A total of 298 patients with hepatectomies was finally included (Supplementary Fig. 1). This study was approved by the Ethics Committee for Human Research, Khon Kaen University (HE641499).

      Recorded data

      Intraoperative data collection comprised sex, age, hepatic resection region, sample size, tumor size, growth patterns, surgical margin, and characteristics of surrounding organs. The liver specimens were examined with relevant tissue blocks taken by a pathologist for routine tissue processing. Formalin-fixed paraffin-embedded (FFPE) tissue blocks were sectioned at 5 microns
      • Patel P.G.
      • Selvarajah S.
      • Boursalie S.
      • How N.E.
      • Ejdelman J.
      • Guerard K.P.
      • et al.
      Preparation of formalin-fixed paraffin-embedded tissue cores for both RNA and DNA extraction.
      and stained with hematoxylin and eosin (H&E). Pathological diagnosis was reviewed for this study in accordance with the 2019 World Health Organization (WHO) classification criteria.
      • Nagtegaal I.D.
      • Odze R.D.
      • Klimstra D.
      • Paradis V.
      • Rugge M.
      • Schirmacher P.
      • et al.
      The 2019 WHO classification of tumours of the digestive system.
      Under light microscopy, the following histomorphological data were recorded - growth patterns, histological type, histological grade, surgical margin, lymphovascular invasion, lymph node metastasis, and distant metastasis. Finally, the gross examination and pathological findings were correlated with the 8th AJCC Staging Manual
      • Amin M.B.
      • Edge S.B.
      • Greene F.L.
      • Byrd D.R.
      • Byrd R.K.
      • Washington M.K.
      • et al.
      AJCC cancer staging manual.
      (Supplementary Table 1). It is noted that under the 8th AJCC staging system, unknown tumor size can be categorized into T2-T4 based on cancer invasion (T2 = intrahepatic vascular invasion, or multiple tumors, with or without vascular invasion, T3 = tumor perforating the visceral peritoneum, and T4 = local extrahepatic invasion) while cases with unknown tumor size/T status (implying any T) but presenting with either lymph node metastasis (N1) and/or distant metastasis status (M1), were stratified into stage IIIB (any TN1M0) and IV (any TN0M1 or any TN1M1), respectively.

      Growth pattern proportion

      The liver resection specimens were serially sectioned, photographed, and tumor growth pattern/s were recorded at the time of gross examination. The growth patterns were estimated as increments of 10% to establish the proportion of each pattern (ID, PI, MF) or combination of patterns (ID + PI, ID + MF, PI + MF, and ID + PI + MF). The growth pattern was also confirmed by microscopic examination by pathologists.

      Histopathological diagnosis

      There were four major histological types found in this study, namely, papillary adenocarcinoma, tubular adenocarcinoma, papillotubular adenocarcinoma and adenocarcinoma (NOS). Papillary, tubular, and papillotubular adenocarcinomas were graded as well- or moderately differentiated and diagnosed according to 2019 WHO classification criteria.
      • Nagtegaal I.D.
      • Odze R.D.
      • Klimstra D.
      • Paradis V.
      • Rugge M.
      • Schirmacher P.
      • et al.
      The 2019 WHO classification of tumours of the digestive system.
      Adenocarcinoma (NOS) was defined as poorly differentiated bile duct cancer, lacking well-formed papillary or tubular formations.

      Statistical analysis

      Only patients with complete datasets were included in the statistical analysis. Statistics for categorical data were performed with the χ2-Test. The Kaplan–Meier model was applied for survival analysis, and the Log-rank test was used to compare factors. Perioperative causes of death were excluded from this analysis. Multivariate analysis was performed using the Cox regression model. For growth pattern estimation, 20% was used as a cut-off value as this figure showed significantly different overall survival (OS) between each pattern (Supplementary Fig. 2).

      Results

      Clinicopathological features correlated with overall survival in iCCA patients

      A surgeon-pathologist team was responsible for the diagnosis and analysis of this cohort of 298 iCCA patients. Using the median age of 60 years (range, 34–79 years), the patients were separated into 2 groups of age ≤60 (n = 119, 40.0%) and >60 years (n = 179, 60.0%). There were 193 males (64.7%) and 105 females (35.3%). The clinicopathological features are described in Table 1. The survival times of the 298 iCCA patients were analyzed with the clinicopathological features by Log-rank test. There was no statistically significant difference in the survival times of the two age groups of patients. Neither did gender affect the survival time (Table 1).
      Table 1Characteristics of intrahepatic cholangiocarcinoma patients from Northeast Thailand with possible clinical and pathological risk factors for survival
      VariablesNo. patients n = 298 (%)Median survival (months)5-year survival (%)Univariate analysisNo. patients (n = 199)Multivariate analysis
      HR ratio (95% CI)P valueHR ratio (95% CI)P value
      Age (years):
       ≤60119 (40.0)1618.21
       >60179 (60.0)1823.30.87 (0.67–1.12)0.277
      Sex:
       Male193 (64.7)1824.71
       Female105 (35.3)1615.91.29 (0.99–1.67)0.054
      Tumor size (cm):
       Tumor in situ21 (7.0)14671.40.25 (0.12–0.55)<0.001
       ≤6105 (35.2)2429.211041
       >696 (32.2)1313.41.79 (1.31–2.44)<0.001951.27 (0.79–2.01)0.323
       Unknown
      With reference to the 8th AJCC staging system, 64/76 cases of unknown tumor size were assigned T2-T4 categories according to presence of tumor invasion. There were 21 cases of intrahepatic vascular invasion, 10 cases with visceral peritoneal involvement, and 33 cases with local extrahepatic invasion).
      76 (25.6)
      Surgical margin (R):
       R0 (in situ)21 (7.0)14671.40.22 (0.10–0.46)<0.001
       R0142 (47.7)2024.511121
       R1135 (45.3)1311.11.61 (1.25–2.08)<0.001870.99 (0.63–1.58)0.133
      Growth patterns:
       ID (in situ)21 (7.0)14671.40.51 (0.21–1.27)0.150
       ID28 (9.4)8657.11251
       PI23 (7.7)164.34.85 (2.45–9.60)<0.001143.62 (1.55–8.46)<0.01
       MF128 (43.0)103.16.27 (3.57–11.02)<0.001834.29 (2.13–8.62)<0.001
       ID + PI21 (7.0)3138.11.68 (0.79–3.57)0.18016
       ID + MF16 (5.4)2943.81.81 (0.82–4.01)0.14114
       PI + MF39 (13.1)145.14.76 (2.55–8.89)<0.001273.57 (1.65–7.74)<0.01
       ID + PI + MF22 (7.4)48501.36 (0.64–2.90)0.42120
      Histological type:
       Histological type (in situ)21 (7.0)14671.40.21 (0.09–0.44)<0.001
       Papillary adenocarcinoma132 (44.3)1920.51911
       Tubular adenocarcinoma117 (39.3)1316.21.39 (1.06–1.82)<0.05870.79 (0.54–1.18)0.249
       Papillotubular adenocarcinoma15 (5.0)166.71.54 (0.87–2.69)0.13310
       Adenocarcinoma, NOS13 (4.4)404.97 (2.74–8.99)<0.001113.44 (1.66–7.13)<0.01
      Histological grade:
       Well-differentiated (in situ)21 (7.0)14671.40.18 (0.09–0.39)<0.001
       Well-differentiated250 (84.0)1718.611771
       Moderately differentiated19 (6.4)710.52.01 (1.22–3.30)<0.01162.37 (1.29–4.36)<0.01
       Poorly differentiated8 (2.6)703.06 (1.50–6.24)<0.0164.51 (1.77–11.50)<0.01
      TNM (8th AJCC staging)

      T category:
       Tis21 (7.0)14671.40.42 (0.18–0.97)<0.05
       T1a39 (13.2)4843.61391
       T1b44 (14.8)21251.86 (1.09–3.17)<0.05441.28 (0.65–2.53)0.471
       T254 (18.1)1923.62.16 (1.30–3.57)<0.01311.66 (0.88–3.14)0.118
       T329 (9.7)1610.33.24 (1.84–5.70)<0.001181.48 (0.71–3.06)0.293
       T499 (33.2)955.03 (3.16–8.01)<0.001672.62 (1.43–4.82)<0.01
       Unknown
      With reference to the 8th AJCC staging system, cases with any T can be staged accordingly if N and/or M are positive. These 12 cases were positive for N and/or M.
      12 (4.0)
      Lymph node metastasis (N):
       N0 (in situ)21 (7.0)14671.40.21 (0.09–0.45)<0.001
       N0185 (62.1)2025.311391
       N192 (30.9)123.22.04 (1.56–2.67)<0.001601.57 (1.07–2.28)<0.05
      Distant metastasis (M):
       M0 (in situ)21 (7.0)14671.40.18 (0.09–0.39)<0.001
       M0255 (85.6)1719.411891
       M122 (7.4)803.26 (2.06–5.16)<0.001102.29 (1.11–4.72)<0.05
      a With reference to the 8th AJCC staging system, 64/76 cases of unknown tumor size were assigned T2-T4 categories according to presence of tumor invasion. There were 21 cases of intrahepatic vascular invasion, 10 cases with visceral peritoneal involvement, and 33 cases with local extrahepatic invasion).
      b With reference to the 8th AJCC staging system, cases with any T can be staged accordingly if N and/or M are positive. These 12 cases were positive for N and/or M.
      Non-invasive CCA (tumor in situ) served as a baseline for good survival time against which all other clinicopathological features were analyzed. Median tumor size, available in 222 patients, was used to divide them into three groups: tumor in situ and tumor size ≤6 cm and >6 cm. Survival analysis showed that patients with tumor size >6 cm [median OS = 13 months (mo.)] had significantly shorter survival than those with tumor size ≤6 cm (OS = 24 mo) (HR = 1.79, p < 0.001); while those with tumor size ≤6 cm had significantly shorter survival than those with a tumor in situ (OS = 24 vs. 146 mo., HR = 0.25, p < 0.001) (Fig. 1a, Table 1).
      Figure 1
      Figure 1Correlation of overall survival of intrahepatic cholangiocarcinoma patients with clinicopathological features. Correlation of overall survival with (a) tumor size, (b) surgical margin, (c) growth patterns, (d) histological type, (e) histological grade, (f) T stage, (g) lymph node metastasis, and (h) distant metastasis
      Surgical margin (R) status was assessed microscopically. Patients with positive surgical margins (R1) had survival times significantly shorter than those with free surgical margins (R0) (OS = 13 vs. 20 mo., HR = 1.61, p < 0.001). In addition, the survival time of R0 in invasive CCA was significantly lower than R0 in non-invasive CCA (OS = 20 vs. 146 mo., HR = 0.22, p < 0.001) (Fig. 1b, Table 1).
      Growth patterns comprised ID in non-invasive CCA, and invasive ID, PI, MF, ID + PI, ID + MF, PI + MF and ID + PI + MF. Results showed that ID (OS = 86 mo) had a significantly better survival time than PI (OS = 86 vs 16 mo, HR = 4.85, p < 0.001), MF (OS = 86 vs 10 mo, HR = 6.27, p < 0.001), and PI + MF (OS = 86 vs 14 mo, HR = 4.76, p < 0.001). However, there was no significant difference when analyzing patterns containing ID components: ID + PI (OS = 86 vs 31 mo, HR = 1.68, p = 0.180), ID + MF (OS = 86 vs 29 mo, HR = 1.81, p = 0.141), ID + PI + MF (OS = 86 vs 48 mo, HR = 1.36, p = 0.421), and ID in non-invasive CCA (OS = 86 vs 146 mo, HR = 0.51, p = 0.150) (Fig. 1c, Table 1).
      The histological type was specified by the pathologists. Tubular adenocarcinoma and adenocarcinoma, NOS, had significantly shorter survival times than papillary type, which is used as the reference group (OS = 13 vs. 19 mo., HR = 1.39, p < 0.05) and (OS = 4 vs. 19 mo., HR = 4.97, p < 0.001), respectively. Additionally, the survival time of papillary type was shorter than histological types with in situ papillary or tubular type (OS = 19 vs. 146 mo., HR = 0.21, p < 0.001). No statistical significance was recorded between papillary and papillotubular types (Fig. 1d, Table 1).
      Histological grades of iCCA comprised well-, moderately and poorly differentiated entities. The OS of patients with well-differentiated tumors was significantly higher than those with moderately (OS = 17 vs. 7 mo., HR = 2.01, p < 0.01) and poorly differentiated tumors (OS = 17 vs. 7 mo., HR = 3.06, p < 0.01). The OS of well-differentiated invasive CCA was markedly shorter than those with well-differentiated in situ lesions (OS = 17 vs. 146 mo., HR = 0.18, p < 0.001) (Fig. 1e, Table 1).
      According to the 8th AJCC staging system, T categories comprise Tis, T1a, T1b, T2, T3, and T4. Results of the survival analysis, using T1a as a reference group showed that T1a (OS = 48 mo) was markedly better than T1b (OS = 48 vs. 21 mo., HR = 1.86, p < 0.05), T2 (OS = 48 vs. 19 mo., HR = 2.16, p < 0.01), T3 (OS = 48 vs. 16 mo., HR = 3.24, p < 0.001), and T4 (OS = 48 vs. 9 mo., HR = 5.03, p < 0.001), while it was significantly shorter than Tis (OS = 48 vs. 146 mo., HR = 0.42, p < 0.05) (Fig. 1f, Table 1).
      For lymph node metastasis (N) and distant metastasis (M), results showed that patients who were either N or M positive had remarkably shorter survival times than those with negative results (OS = 12 vs. 20 mo., HR = 2.04, p < 0.001) and (OS = 8 vs. 17 mo., HR = 3.26, p < 0.001), respectively. As expected, invasive CCA with negative N and M status correlated with significantly shorter survival times than in situ tumors (OS = 20 vs. 146 mo., HR = 0.21, p < 0.001) and (OS = 17 vs. 146 mo., HR = 0.18, p < 0.001), respectively (Fig. 1g, h, Table 1).
      Significant factors such as tumor size, surgical margin, growth patterns, histological type, histological grade, and T, N, and M categories, identified in the univariate analysis of survival were selected for further investigation by multivariate analysis to investigate independent factors for prognostic markers in iCCA. For multivariate analysis, only invasive CCA was analyzed after removing non-invasive/in situ cases.

      Independent risk factors for prognostic prediction of survival

      To determine prognostic markers, multivariate analysis was performed to consider possible features that had significantly affected the survival times of iCCA patients in univariate analysis (Table 1). 99 patients with unknown tumor size were excluded. For multivariate analysis, features comprising tumor size, surgical margin, growth patterns, histological type, histological grade, T category, lymph node metastasis, and distant metastasis were identified in 199 patients by univariate analysis. Further analysis revealed that growth patterns, histological type, histological grade, lymph node metastasis, and distant metastasis were independent risk factors for predicting poor outcomes in iCCA patients (Table 1).
      ID was used as a reference group for the comparison of growth patterns in multivariate analysis. Results showed that PI, MF, and PI + MF had hazard ratios significantly higher than ID (HR = 3.62, 4.29, and 3.57, p < 0.01, 0.001, and 0.01), respectively. There was no statistical significance when ID was compared with ID + PI, ID + MF, and ID + PI + MF. This finding suggested that the presence of ID components was a favorable prognostic factor for iCCA patients. The corollary is that lack of ID component is a poor prognostic factor for survival.
      For histological types, invasive papillary adenocarcinoma was used as the reference group for comparison with other types. Adenocarcinoma, NOS, had HR markedly higher than papillary type (HR = 3.44, p < 0.01). However, no statistically significant difference was observed when compared to the tubular type (HR = 0.79, p = 0.249).
      For histological grades, the moderately and poorly differentiated tumors had HR markedly higher than the well-differentiated reference group (HR = 2.37 and 4.51, p < 0.01) in multivariate analysis.
      Lymph node metastasis and distant metastasis were consistent risk factors for poor prognosis. Multivariate results showed that positive lymph node and distant metastasis had HR significantly greater than when they were negative (HR = 1.57, p < 0.05; and HR = 2.29, p < 0.05), respectively.
      This study showed that growth patterns (PI, MF, and PI + MF), histological type (adenocarcinoma, NOS), histological grade (moderate and poor differentiation) (Fig. 2a, b), lymph node metastasis, and distant metastasis were prognostic risk factors for poor survival.
      Figure 2
      Figure 2Intrahepatic cholangiocarcinoma. (a) Growth patterns seen on gross inspection of hepatectomies: non-invasive intraductal (ID), invasive ID, periductal-infiltrating (PI), mass-forming (MF), combination of PI and MF, and combination of ID + PI + MF. (b) Histological types and grades: Well-differentiated intraductal papillary carcinoma (tumor in situ) and well-differentiated papillary adenocarcinoma (invasive) (1st row, left & right); well-differentiated tubular adenocarcinoma and well-differentiated papillotubular adenocarcinoma (2nd row, left & right); moderately differentiated tubular adenocarcinoma and poorly differentiated adenocarcinoma, not otherwise specified (3rd row, left & right) (Hematoxylin & eosin, x 3 mm and 200 μm)
      We thus proposed the Khon Kaen University (KKU) staging system by incorporating additional prognostic risk factor to modify 8th AJCC stages IB, II, and IIIA. The modification criteria were based on growth patterns, an independent factor identified in the multivariate analysis. The limited number of cases precluded the incorporation of histological type and grade into the modification of 8th AJCC staging system.

      The incorporation of additional factors for prognostication improved the 8th AJCC staging system

      TNM staging was performed on iCCA patients according to the 8th AJCC staging system. The survival analysis showed that stage IA patients had no statistically significant difference in survival time with IB (OS = 31 vs. 29 mo., HR = 1.22, p = 0.509), II (OS = 31 vs. 24 mo., HR = 1.17, p = 0.564), and IIIA (OS = 31 vs. 20 mo., HR = 1.92, p = 0.052), while the survival time was significantly better than for IIIB (OS = 31 vs. 11 mo., HR = 3.24, p < 0.001), and IV (OS = 31 vs. 8 mo., HR = 6.96, p < 0.001) (Fig. 3a). It was observed that stages IA, IB, II, and IIIA showed distinct ambiguity of survival times and rates. There was no statistically significant difference between IIIA and IIIB; all of this may impact prognosis and treatment decisions.
      Figure 3
      Figure 3Overall survival of intrahepatic cholangiocarcinoma patients with TNM stages by (a) AJCC and (b) KKU staging system (∗, ∗∗ and∗∗∗ represent p < 0.05, 0.01 and 0.001, respectively; ns = no significant statistical difference)
      The KKU staging system separated iCCA patients staged by 8th AJCC staging into two main groups – those with intraductal growth components and those without intraductal growth components. There are five KKU stages comprising I, II, IIIA, IIIB, and IV, with up- and downstaging assigned as described in Table 2.
      Table 2Modification of the 8th AJCC/UICC staging system for intrahepatic cholangiocarcinoma to the Khon Kaen University (KKU) staging system developed in Northeast Thailand
      TNM staging (8th AJCC/UICC staging)KKU stagingDescription
      Stage 0 = TisN0M0KKU Stage 0Same as 8th AJCC staging system
      Stage I = T1N0M0KKU Stage IStage I + Invasive intraductal growth components
      ID, ID + PI, ID + MF and ID + PI + MF.
      Stage IB = T1bN0M0
      Stage II = T2N0M0KKU Stage IIStage II-IIIA + Invasive intraductal growth components
      Stage IIIA = T3N0M0KKU Stage IIIAStage IIIB + Invasive intraductal growth components or stage I-IIIA + Growth pattern without ID components
      PI, MF, and PI + MF.
      Stage IIIB = T4N0M0, TAnyN1M0KKU Stage IIIBStage IIIB + Growth pattern without ID components
      Stage IV = anyTanyNM1KKU Stage IVSame as 8th AJCC staging system
      a ID, ID + PI, ID + MF and ID + PI + MF.
      b PI, MF, and PI + MF.
      The 8th AJCC TNM stage IA, IB, II or IIIA, and stage IIIB with growth patterns lacking ID components (i.e., PI, MF, or PI + MF) were upstaged or converted to KKU stage IIIA and IIIB, respectively. In this study, 49 cases of AJCC stage IA-IIIA were upstaged to KKU stage IIIA, while 91 cases of AJCC stage IIIB were converted to KKU stage IIIB, based on growth pattern classification.
      For the downstaging of the 8th AJCC TNM stages, ID components (ID, ID + PI, ID + MF, and ID + PI + MF) have shown better survival times than growth patterns without ID components. In this study, 25 cases of AJCC stage IA and IB were converted to KKU stage I. Furthermore, 13 and 18 cases of AJCC stage II/IIIA and IIIB were downstaged to KKU stage II and IIIA, respectively, based on the presence of ID components.
      The classification performance of the KKU staging system can distinguish good and poor outcomes in iCCA patients. The results showed that KKU stage I had OS and survival rate better than KKU stage IIIA (OS = 102 vs 19 mo, survival rate = 56.1% vs 13.5%, HR = 4.02, p < 0.001), IIIB (OS = 102 vs 10 mo, survival rate = 56.1% vs 0%, HR = 8.43, p < 0.001), and IV (OS = 102 vs 8 mo, survival rate = 56.1% vs 0%, HR = 14.84, p < 0.001). It is of note that there was no statistically significant difference in the early stages of KKU staging (0 vs I, 0 vs II and I vs II) where cases of iCCA were largely composed of ID components. Moreover, the proposed model could significantly separate each KKU stage: II vs. IIIA (p < 0.001), IIIA vs. IIIB (p < 0.001), and IIIB vs. IV (p < 0.05) (Fig. 3b).
      However, this criterion of growth pattern cannot be used for 8th AJCC stage IV due to the presence of distant metastasis. Although ID components are associated with favorable survival times, other factors in the advanced stage IV may have adverse effects on survival (Fig. 3a, b). We have retained stage 0 of the 8th AJCC staging system, as all cases of stage 0 in our cohort exhibited pure ID, representing good survival in the early stage.

      Discussion

      Southeast Asia has a high incidence of iCCA, particularly in Thailand. Treeprasertsuk et al. reported an incidence rate of 14.6 per 100,000 populations per year of iCCA in Thailand during the period 2009–2013. iCCA patients have a high mortality rate of approximately 14%.
      • Treeprasertsuk S.
      • Poovorawan K.
      • Soonthornworasiri N.
      • Chaiteerakij R.
      • Thanapirom K.
      • Mairiang P.
      • et al.
      A significant cancer burden and high mortality of intrahepatic cholangiocarcinoma in Thailand: a nationwide database study.
      The median survival time for Thai patients with late stages of CCA is around five months with palliative therapy.
      • Prachayakul V.
      • Chaisayan S.
      • Aswakul P.
      • Deesomsak M.
      Clinical characteristics and treatment outcomes of patients with unresectable cholangiocarcinoma in Thailand: are there differences dependent on stent type?.
      CCA patients, especially iCCA, with advanced stages III-IV, have an approximately 6.8-fold higher mortality rate than stages I–II.
      • Thunyaharn N.
      • Promthet S.
      • Wiangnon S.
      • Suwanrungruang K.
      • Kamsa-ard S.
      Survival of cholangiocarcinoma patients in northeastern Thailand after supportive treatment.
      Our study cohort showed similar dismal outcomes. Advanced cases (stage III-IV) comprised approximately 57% of our cohort with a mortality rate approximately 4-fold higher than for stage I-II. It is hoped that precise diagnosis and staging of early CCA patients may provide prompt treatment with a better outcome.
      The 8th AJCC/UICC Staging Manual is standard guidance for classifying cancer prognosis and treatment decisions. It was upgraded from the 7th edition,
      • Brierley J.D.
      • Gospodarowicz M.K.
      • Wittekind C.
      TNM classification of malignant tumours.
      and reports have shown that the 8th edition has improved diagnosis precision and treatment decisions for CCA patients.
      • Kim Y.
      • Moris D.P.
      • Zhang X.F.
      • Bagante F.
      • Spolverato G.
      • Schmidt C.
      • et al.
      Evaluation of the 8th edition American Joint Commission on Cancer (AJCC) staging system for patients with intrahepatic cholangiocarcinoma: a surveillance, epidemiology, and end results (SEER) analysis.
      • Spolverato G.
      • Bagante F.
      • Weiss M.
      • Alexandrescu S.
      • Marques H.P.
      • Aldrighetti L.
      • et al.
      Comparative performances of the 7th and the 8th editions of the American Joint Committee on Cancer staging systems for intrahepatic cholangiocarcinoma.
      • Kang S.H.
      • Hwang S.
      • Lee Y.J.
      • Kim K.H.
      • Ahn C.S.
      • Moon D.B.
      • et al.
      Prognostic comparison of the 7th and 8th editions of the American Joint Committee on Cancer staging system for intrahepatic cholangiocarcinoma.
      In a validation study using the SEER database to compare the stratification of the two editions, Kim et al. analyzed 1008 patients who underwent surgical resection for iCCA. Results showed that Harrell's concordance index for overall survival in the 8th edition was better than the 7th, resulting in improved stratification.
      • Kim Y.
      • Moris D.P.
      • Zhang X.F.
      • Bagante F.
      • Spolverato G.
      • Schmidt C.
      • et al.
      Evaluation of the 8th edition American Joint Commission on Cancer (AJCC) staging system for patients with intrahepatic cholangiocarcinoma: a surveillance, epidemiology, and end results (SEER) analysis.
      Spolverato et al. also validated the performance of the 8th edition in 1154 patients who underwent hepatectomy. The ambiguous hazard ratio in T2a and T2b was higher than T3 in the 7th edition. This paradoxical staging was addressed in the 8th edition by the new category in T3, defined as perforation of the visceral peritoneum or serosal invasion.
      • Spolverato G.
      • Bagante F.
      • Weiss M.
      • Alexandrescu S.
      • Marques H.P.
      • Aldrighetti L.
      • et al.
      Comparative performances of the 7th and the 8th editions of the American Joint Committee on Cancer staging systems for intrahepatic cholangiocarcinoma.
      However, several reports have emerged citing some deficiencies in the 8th AJCC staging regarding discriminatory ability and classification efficiency. It is perceived that there is a need for additional independent factors.
      • Cheng Z.
      • Lei Z.
      • Si A.
      • Yang P.
      • Luo T.
      • Guo G.
      • et al.
      Modifications of the AJCC 8th edition staging system for intrahepatic cholangiocarcinoma and proposal for a new staging system by incorporating serum tumor markers.
      • Meng Z.W.
      • Pan W.
      • Hong H.J.
      • Chen J.Z.
      • Chen Y.L.
      Macroscopic types of intrahepatic cholangiocarcinoma and the eighth edition of AJCC/UICC TNM staging system.
      • Yamamoto Y.
      • Sugiura T.
      • Okamura Y.
      • Ito T.
      • Ashida R.
      • Ohgi K.
      • et al.
      The evaluation of the eighth edition of the AJCC/UICC staging system for intrahepatic cholangiocarcinoma: a proposal of a modified new staging system.
      • Zhang X.F.
      • Lv Y.
      • Weiss M.
      • Popescu I.
      • Marques H.P.
      • Aldrighetti L.
      • et al.
      Should utilization of lymphadenectomy vary according to morphologic subtype of intrahepatic cholangiocarcinoma?.
      • Bartsch F.
      • Baumgart J.
      • Hoppe-Lotichius M.
      • Straub B.K.
      • Heinrich S.
      • Lang H.
      Intrahepatic cholangiocarcinoma - influence of resection margin and tumor distance to the liver capsule on survival.
      • Padthaisong S.
      • Thanee M.
      • Namwat N.
      • Phetcharaburanin J.
      • Klanrit P.
      • Khuntikeo N.
      • et al.
      Overexpression of a panel of cancer stem cell markers enhances the predictive capability of the progression and recurrence in the early stage cholangiocarcinoma.
      In 2020, Yamamoto et al. reported that the 8th AJCC could not distinguish between T2, T3, and T4 for the 5-year disease-specific survival (DSS) of iCCA. They applied independent factors from multivariate analysis such as tumor size (cut-off 2 cm for T1 and T2), vascular invasion or perforation of the visceral peritoneum (T3), and multiple tumors or growth pattern (PI type, T4), for a new staging for their study with improved stratification performance in DSS.
      • Yamamoto Y.
      • Sugiura T.
      • Okamura Y.
      • Ito T.
      • Ashida R.
      • Ohgi K.
      • et al.
      The evaluation of the eighth edition of the AJCC/UICC staging system for intrahepatic cholangiocarcinoma: a proposal of a modified new staging system.
      In another validation study of 1601 iCCA patients, Cheng et al. proposed adding serum tumor markers, CA19-9 and CEA, as independent factors for better classification performance of stage IIIA, IIIB, and IV.
      • Cheng Z.
      • Lei Z.
      • Si A.
      • Yang P.
      • Luo T.
      • Guo G.
      • et al.
      Modifications of the AJCC 8th edition staging system for intrahepatic cholangiocarcinoma and proposal for a new staging system by incorporating serum tumor markers.
      Brustia et al. highlighted the ambiguous classification of survival curves following T categorization in the 8th edition with patients having T2, T3, and T4 disease exhibiting overlapping overall survival. To overcome these discrepancies, the iCCA staging system was modified using the HR of the prognostic factors. They proposed a preoperative risk score (PRS) which was first reported by Sasaki et al.
      • Sasaki K.
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      • Andreatos N.
      • Fonseca F.
      • Weiss M.
      • Barbon C.
      • et al.
      Preoperative risk score and prediction of long-term outcomes after hepatectomy for intrahepatic cholangiocarcinoma.
      The PRS score was calculated from independent factors including albumin, neutrophil-to-lymphocyte-ratio, CA19-9, and tumor size.
      Combining the PRS score and the 8th AJCC staging can correct the problem of overlapping overall survival in T2, T3, and T4 categories and classify ICC patients with sufficient prognostic difference.
      • Brustia R.
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      Preoperative risk score for prediction of long-term outcomes after hepatectomy for intrahepatic cholangiocarcinoma: report of a collaborative, international-based, external validation study.
      Cancer biomarkers, such as cancer stem cell markers (CD44v6, 8–10, CD133, EpCAM, and ALDH1A1), are also favored to enhance capacity for prognostication of CCA and have been used as additional factors for prediction of recurrence in early-stage disease.
      • Padthaisong S.
      • Thanee M.
      • Namwat N.
      • Phetcharaburanin J.
      • Klanrit P.
      • Khuntikeo N.
      • et al.
      Overexpression of a panel of cancer stem cell markers enhances the predictive capability of the progression and recurrence in the early stage cholangiocarcinoma.
      Similarly, our study showed that the 8th edition did not satisfactorily classify the prognosis of iCCA in the Thai OV.-associated CCA cohort. It showed ambiguous classification in stages IA, IB, II, and IIIA with overlapping OS. The survival time and rate in early stage disease (OS = 20–31 mo, 5year-survival rate = 23.5–36.8%) were close to advanced stages IIIB and IV (OS = 11 and 8 mo, 5year-survival rate = 6.1 and 0%, respectively). The unsatisfactory performance of the 8th AJCC staging system when applied to our cohort may affect prognosis and treatment options. This study proposed an alternative model by modification of the 8th AJCC staging system to provide better discriminatory capacity suited to our population. Our study revealed no statistically significant difference in OS for each stage, and the survival rate of each stage by 8th AJCC staging showed very low or no statistical significance in stage IA-IIIA iCCA patients. Paradoxically, these results may reduce diagnostic capability and precision due to a misalliance or disparity in the treatment plan. Therefore, there is a need to modify the 8th AJCC staging for iCCA in the Thai cohort for appropriate diagnosis and treatment. Three independent factors; growth patterns, histological type, and histological grade, showed a significant effect on the survival rate of iCCA patients by multivariate analysis. This study included only growth patterns as additional factors to modify 8th AJCC staging, while histological type and grade were deemed less major additional factors. The 8th AJCC staging was used as base clustering for iCCA patient classification, and growth pattern was used for a subclassification to create the KKU staging system. This alternative model led to subsequent down- and upstaging of iCCA patients based on the OS period of 8th AJCC-staged CCA.
      Growth pattern is considered one of the impact predictors for the prognosis and staging of iCCA. ID growth type favors good survival. Conversely, PI and MF are related to poor outcomes.
      • Yamasaki S.
      Intrahepatic cholangiocarcinoma: macroscopic type and stage classification.
      ,
      • Shimada K.
      • Sano T.
      • Sakamoto Y.
      • Esaki M.
      • Kosuge T.
      • Ojima H.
      Surgical outcomes of the mass-forming plus periductal infiltrating types of intrahepatic cholangiocarcinoma: a comparative study with the typical mass-forming type of intrahepatic cholangiocarcinoma.
      ,
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      • Chamadol N.
      • Laopaiboon V.
      • Thuanman J.
      • Thinkhamrop K.
      • et al.
      Survival after surgery among patients with cholangiocarcinoma in Northeast Thailand according to anatomical and morphological classification.
      ,
      • Hwang S.
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      • et al.
      Prognostic impact of tumor growth type on 7th AJCC staging system for intrahepatic cholangiocarcinoma: a single-center experience of 659 cases.
      ,
      • Ohtsuka M.
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      • et al.
      Results of surgical treatment for intrahepatic cholangiocarcinoma and clinicopathological factors influencing survival.
      Literature search revealed that most published studies did not specifically address the proportions of the individual growth patterns when they occurred in mixed combinations, for the purpose of relating to survival times.
      • Tawarungruang C.
      • Khuntikeo N.
      • Chamadol N.
      • Laopaiboon V.
      • Thuanman J.
      • Thinkhamrop K.
      • et al.
      Survival after surgery among patients with cholangiocarcinoma in Northeast Thailand according to anatomical and morphological classification.
      ,
      • Chung T.
      • Rhee H.
      • Nahm J.H.
      • Jeon Y.
      • Yoo J.E.
      • Kim Y.J.
      • et al.
      Clinicopathological characteristics of intrahepatic cholangiocarcinoma according to gross morphologic type: cholangiolocellular differentiation traits and inflammation- and proliferation-phenotypes.
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      Cholangiocarcinoma 2020: the next horizon in mechanisms and management.
      • Bagante F.
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      • Marques H.P.
      • Aldrighetti L.
      • et al.
      Impact of morphological status on long-term outcome among patients undergoing liver surgery for intrahepatic cholangiocarcinoma.
      Yamamoto et al. modified the T category of 8th AJCC staging system by using tumor size of 2 cm for separating T1 and T2, and growth pattern PI type for T4. This new T category provided better separation of T1, T2, T3 and T4 than the 8th AJCC staging system. Moreover, TNM staging of the new model improved stratification performance in stages II, IIIA, and IIIB.
      • Banales J.M.
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      • et al.
      Cholangiocarcinoma 2020: the next horizon in mechanisms and management.
      The impact of growth pattern in modifying the T category of 8th AJCC staging system was also reported by Bagante et al. They incorporated growth patterns, including IG (or ID in our study), PI, and MF, into the T category. In this new T category, IG + MF denoting good outcome was used to modify T1 and T3, while PI + MF indicating poor outcome was incorporated into T2 and T4. Thereby, the new T category comprising new T1 = T1+(IG + MF), T2 = T2+(PI + MF), T3 = T3+(IG + MF), and T4 = T4+(PI + MF) showed more satisfactory separation than the original T category of 8th AJCC staging system.
      • Bagante F.
      • Spolverato G.
      • Weiss M.
      • Alexandrescu S.
      • Marques H.P.
      • Aldrighetti L.
      • et al.
      Impact of morphological status on long-term outcome among patients undergoing liver surgery for intrahepatic cholangiocarcinoma.
      This information supports the contention that growth pattern can be used to modify 8th AJCC staging system. There are, however, some limitations. In a case of a mixed type growth pattern, there are no clear cut-point criteria to separate each component of the mixed pattern. Our study is apparently the first to propose a cut-off value for identification of the proportions of the individual growth patterns. Our findings suggested that a 20% cut-off was the optimal value in our cohort of iCCA patients for achieving better survival differentiation than 10%, which appeared too loose as a criterion, and 30% is too rigorous (Supplementary Fig. 2). Although growth pattern is not recorded for stratification in the 8th edition, it is strongly suggested as an additional factor for the prediction of patient outcome and for modifying the 8th AJCC staging.
      • Shimada K.
      • Sano T.
      • Sakamoto Y.
      • Esaki M.
      • Kosuge T.
      • Ojima H.
      Surgical outcomes of the mass-forming plus periductal infiltrating types of intrahepatic cholangiocarcinoma: a comparative study with the typical mass-forming type of intrahepatic cholangiocarcinoma.
      ,
      • Meng Z.W.
      • Pan W.
      • Hong H.J.
      • Chen J.Z.
      • Chen Y.L.
      Macroscopic types of intrahepatic cholangiocarcinoma and the eighth edition of AJCC/UICC TNM staging system.
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      • Okamura Y.
      • Ito T.
      • Ashida R.
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      • et al.
      Should utilization of lymphadenectomy vary according to morphologic subtype of intrahepatic cholangiocarcinoma?.
      Our study found that patients with growth patterns comprising PI, MF, and PI + MF showed poor survival rates, as previously reported.
      • Yamasaki S.
      Intrahepatic cholangiocarcinoma: macroscopic type and stage classification.
      ,
      • Shimada K.
      • Sano T.
      • Sakamoto Y.
      • Esaki M.
      • Kosuge T.
      • Ojima H.
      Surgical outcomes of the mass-forming plus periductal infiltrating types of intrahepatic cholangiocarcinoma: a comparative study with the typical mass-forming type of intrahepatic cholangiocarcinoma.
      ,
      • Hwang S.
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      Interestingly, growth patterns with pure ID or ID components (ID + PI, ID + MF, and ID + PI + MF) showed a better survival rate than those without ID components (PI, MF, and PI + MF) (Table 1, Fig. 1c). Therefore, in the KKU staging, patients in stage IA, IB, II, IIIA, and IIIB with ID components were clustered separately from patients with other growth patterns, PI, MF, and PI + MF. Table 2 showed the stratification of iCCA patients into four groups to create KKU staging system: stage I, II, and IIIA (modified by downstaging or converting AJCC stage IA-IIIB with ID components), and IIIA and IIIB (modified by upstaging or converting AJCC stage IA-IIIB without ID components). 38 cases of AJCC stage IA-IIIA and 18 cases of IIIB were downstaged or converted to KKU stage I, II, and IIIA, respectively. On the other hand, AJCC stages were upstaged in patients with PI, MF, and PI + MF growth patterns.
      • Yamasaki S.
      Intrahepatic cholangiocarcinoma: macroscopic type and stage classification.
      ,
      • Tawarungruang C.
      • Khuntikeo N.
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      • Thuanman J.
      • Thinkhamrop K.
      • et al.
      Survival after surgery among patients with cholangiocarcinoma in Northeast Thailand according to anatomical and morphological classification.
      ,
      • Suh K.S.
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      • Kim S.H.
      • Lee K.U.
      Clinical outcomes and apomucin expression of intrahepatic cholangiocarcinoma according to gross morphology.
      These criteria upstaged or converted 49 cases of stage IA-IIIA and 91 cases of stage IIIB of the 8th AJCC staging system to the KKU staging system. The stratification performance of the KKU staging system showed that it could separate each stage and provide an expected projected outcome for each stage (Fig. 3b). The OS and survival rate were significantly distinct after classification by the KKU staging system when compared between KKU stage I-II (composed of ID components) and IIIA-IIIB (commonly composed of PI, MF, and PI + MF).
      In this study, we included only growth patterns for modifying the 8th AJCC staging, although histological type and grade were revealed as high-risk factors for poor survival. Studies have reported the correlation between histological type and grade with adverse clinicopathological features.
      • Haswell-Elkins M.R.
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      • Sithithaworn P.
      • et al.
      Liver fluke infection and cholangiocarcinoma: model of endogenous nitric oxide and extragastric nitrosation in human carcinogenesis.
      ,
      • Shimada K.
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      • Sakamoto Y.
      • Esaki M.
      • Kosuge T.
      • Ojima H.
      Surgical outcomes of the mass-forming plus periductal infiltrating types of intrahepatic cholangiocarcinoma: a comparative study with the typical mass-forming type of intrahepatic cholangiocarcinoma.
      ,
      • Meng Z.W.
      • Pan W.
      • Hong H.J.
      • Chen J.Z.
      • Chen Y.L.
      Macroscopic types of intrahepatic cholangiocarcinoma and the eighth edition of AJCC/UICC TNM staging system.
      • Yamamoto Y.
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      • Okamura Y.
      • Ito T.
      • Ashida R.
      • Ohgi K.
      • et al.
      The evaluation of the eighth edition of the AJCC/UICC staging system for intrahepatic cholangiocarcinoma: a proposal of a modified new staging system.
      • Zhang X.F.
      • Lv Y.
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      • Marques H.P.
      • Aldrighetti L.
      • et al.
      Should utilization of lymphadenectomy vary according to morphologic subtype of intrahepatic cholangiocarcinoma?.
      ,
      • Choi S.B.
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      • Choi J.S.
      • Lee W.J.
      • et al.
      The prognosis and survival outcome of intrahepatic cholangiocarcinoma following surgical resection: association of lymph node metastasis and lymph node dissection with survival.
      ,
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      • Chen Y.L.
      Modified staging classification for intrahepatic cholangiocarcinoma based on the sixth and seventh editions of the AJCC/UICC TNM staging systems.
      Choi et al. reported that poorly differentiated histological grade is an independent prognostic factor for disease-free survival and associated lymph node metastasis.
      • Choi S.B.
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      • et al.
      The prognosis and survival outcome of intrahepatic cholangiocarcinoma following surgical resection: association of lymph node metastasis and lymph node dissection with survival.
      Similarly, Zhu et al. revealed that poor histological differentiation is an independent risk factor for poor outcome in iCCA. It was used as one of the independent factors to modify the 6th and 7th editions of AJCC staging to improve precision classification of staging.
      • Meng Z.W.
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      Modified staging classification for intrahepatic cholangiocarcinoma based on the sixth and seventh editions of the AJCC/UICC TNM staging systems.
      In this study, we found that poor differentiation correlated with growth patterns without ID components, especially MF. This observation supported the contention that incorporating growth patterns such as PI, MF, and PI + MF was sufficient to represent adverse status. This alternative staging method could improve the stratification and treatment performance of iCCA in Northeast Thailand cohort.
      Our proposed alternative KKU staging system has three strong points. Firstly, the KKU system stratified patients into relatively well (early stage: OS of I and II = 102 and 67 mo, respectively) and poor (late stage: OS of IIIA, IIIB and IV = 19, 10 and 8, respectively) outcomes. On the other hand, the 8th AJCC staging system when applied to our cohort showed short-term survivals and too close a gap between the outcomes of early stages (OS of IA, IB and II = 31, 29 and 24 mo, respectively) and late stages (OS of IIIA, IIIB and IV = 20, 11 and 8 mo, respectively). Secondly, the KKU system showed significantly better separation of stage II (early stage) and IIIA (late stage) than the 8th AJCC staging system. Finally, the KKU system is not too difficult to apply in other cohorts because growth pattern histomorphology has been reported in standard guidelines (College of American Pathologists CAPs protocol) and many other reports. Therefore, we hope that the KKU staging system might be viewed as an alternative system for classifying iCCA in other cohorts that may have encountered ambiguous classification performance with the 8th AJCC staging system.
      There are several limitations to this study. The proposed KKU staging system was studied in a single institution in Northeast Thailand. Overall survival and not disease-specific survival was analyzed. The small number of patients in certain growth patterns, such as PI (n = 23), ID + PI (n = 21), ID + MF (n = 16) and ID + PI + MF (n = 22), do not adequately represent the rest of the patient population. Histological type and grade are commonly reported characteristics in cancer prognostication and important independent risk factors for stratifying patients; further analysis with recruitment of more patients is planned for subsequent incorporation into the KKU model to better stratify early stage I and II cases. There was also no available follow-up data on adjuvant therapy; thereby significantly curtailing the evaluation of surgical margin status. Prospective studies with internal and external validation of the KKU staging system are needed to verify the discriminatory performance for prognostic stratification of iCCA patients in other study cohorts.
      It is hoped that after validation is completed, the KKU staging system will employed in clinical staging and for pre-operative detection of pre-invasive neoplasms of the bile ducts in conjunction with radiological studies.
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      In 2017, Luvira V. and Eurboonyanun K (co-authors in our study) investigated intraductal papillary neoplasms of the bile duct (IPNB) with survival correlation of CCA patients via radio-pathological staging. Their study showed that IPNB correlated with early stage and predicted survival very well
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      • Luvira V.
      • Bhudhisawasdi V.
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      Morphological classification of intraductal papillary neoplasm of the bile duct with survival correlation.
      ,
      • Sungkasubun P.
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      • Sricharunrat T.
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      Ultrasound screening for cholangiocarcinoma could detect premalignant lesions and early-stage diseases with survival benefits: a population-based prospective study of 4,225 subjects in an endemic area.
      In the future, this study will be modified for incorporation into the KKU staging system in guiding planning of surgical procedures. Several other studies have also employed pre-operative radiographic imaging on ID lesions for radiological diagnosis to predict prognosis of CCA.
      • Nakanuma Y.
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      • Kakuda Y.
      • Sugino T.
      • Kubota K.
      • Furukawa T.
      • et al.
      Intraductal papillary neoplasm of bile duct: updated clinicopathological characteristics and molecular and genetic alterations.
      ,
      • Sungkasubun P.
      • Siripongsakun S.
      • Akkarachinorate K.
      • Vidhyarkorn S.
      • Worakitsitisatorn A.
      • Sricharunrat T.
      • et al.
      Ultrasound screening for cholangiocarcinoma could detect premalignant lesions and early-stage diseases with survival benefits: a population-based prospective study of 4,225 subjects in an endemic area.
      • Siripongsakun S.
      • Sapthanakorn W.
      • Mekraksakit P.
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      • Chonyuen S.
      • Seetasarn J.
      • et al.
      Premalignant lesions of cholangiocarcinoma: characteristics on ultrasonography and MRI.
      • Joo I.
      • Lee J.M.
      • Yoon J.H.
      Imaging diagnosis of intrahepatic and perihilar cholangiocarcinoma: recent advances and challenges.
      • Kim H.
      • Lim J.H.
      • Jang K.T.
      • Kim M.J.
      • Lee J.
      • Lee J.Y.
      • et al.
      Morphology of intraductal papillary neoplasm of the bile ducts: radiologic-pathologic correlation.
      • Park H.J.
      • Kim S.Y.
      • Kim H.J.
      • Lee S.S.
      • Hong G.S.
      • Byun J.H.
      • et al.
      Intraductal papillary neoplasm of the bile duct: clinical, imaging, and pathologic features.
      In summary, in this retrospective study spanning 2002 to 2017, we updated important information on the staging of iCCA. About 57% of a total of 298 iCCA from Northeast Thailand presented with late-stage disease (TNM stages IIIA and IIIB, 50%) and distant metastasis (stage IV, 7%). All of these patients had poor survival outcomes. This study corroborated that tumor size, surgical margin, growth patterns, histological type, histological grade, and TNM stages are factors that impact survival outcomes. Furthermore, we demonstrated that growth patterns, histological type, and histological grade are prognostic markers for predicting poor survival of iCCA patients. Employing growth pattern as an additional risk factor to refine the 8th AJCC staging system, we developed the KKU staging system to assess iCCA patients in Northeast Thailand. There is currently a prospective study where KKU staging is applied to iCCA patients to validate its utility as a prognostic and predictive tool and guidance to treatment options.

      Authors’ contributions

      Conceptualization, PS, SK CA, SS, and PI; funding acquisition, SK; sample colloction and diagnosis, PS, SK, CA, SS, PI, WK, NK, AT, AJ, VT, TS, VL, KE, WL and JP; analysis and interpretion of data, PS, SK, CA and PP; supervision, SK; writing original draft, PS, SK, CA SS, PI and PP; writing review and editing PS, SK, CA SS, PI, WK, WB, MT, AW and PP. All authors approved the final version of the manuscript.

      Acknowledgements

      This research was supported by NSRF under the Basic Research Fund of Khon Kaen University through Cholangiocarcinoma Research Institute (CARI). The authors would like to acknowledge Assoc. Prof. Dr. Chawalit Pairojkul and Prof. Dr. Banchob Sripa from Department of Pathology, Faculty of Medicine, Khon Kaen University, Thailand for helpful discussions. Additionally, all authors are truly grateful to Assoc. Prof. Dr. Bandit Thinkhamrop at Data Management and Statistical Analysis Center (DAMASAC), Faculty of Public Health, Khon Kaen University, Thailand for suggesting statistical analysis. We are also indebted to all members of CASCAP, particularly the cohort members, and researcher at Department of Pathology, Faculty of Medicine, Khon Kaen University for collecting and proofing of CCA patient data.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:

      Funding

      We would like to acknowledge the Cholangiocarcinoma Screening and Care Program (CASCAP) under Cholangiocarcinoma Research Institute (CARI), Khon Kaen University, Khon Kaen, Thailand, and The National Research Council of Thailand through Fluke Free Thailand project, Khon Kaen University through Cholangiocarcinoma Research Institute to support funding.

      Conflicts of interest

      None to declare.

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