Review to better understand the macroscopic subtypes and histogenesis of intrahepatic cholangiocarcinoma

Abstract

Intrahepatic cholangiocarcinoma is macroscopically classified into three subtypes, mass-forming-type, periductal infiltrating-type, and intraductal growth-type. Each subtype should be preoperatively differentiated to perform the valid surgical resection. Recent researches have revealed the clinical, radiologic, pathobiological characteristics of each subtype. We reviewed recently published studies covering various aspects of intrahepatic cholangiocarcinoma (ICC), focusing especially on the macroscopic subtypes and stem cell features to better understand the pathophysiology of ICC and to establish the valid therapeutic strategy.

Key Words: Intrahepatic cholangiocarcinoma, Combined hepatocellular-cholangiocarcinoma, Hepatic progenitor cells, Macroscopic subtype

Core tip: We reviewed recently published studies covering various aspects of intrahepatic cholangiocarcinoma (ICC), focusing especially on the macroscopic subtypes and stem cell features to better understand the pathophysiology of ICC and to establish the valid therapeutic strategy.

INTRODUCTION

The Liver Cancer Study Group of Japan has applied the same TNM staging system used for hepatocellular carcinoma (HCC) to that for intrahepatic cholangiocarcinoma (ICC)[1]. A recent increase in the number of surgically resected cases of ICC has clarified some characteristics inherent in this disease. The most prominent feature of ICC is that of the macroscopic findings reflecting its growth patterns. ICC is grossly classifiable into mass-forming (MF), periductal infiltrating (PI), and intraductal growth (IG) types[2]. The MF type presents as a gray to gray-white, firm and solid mass in the hepatic parenchyma, and of these three subtypes, MF-type ICC is the most common (59%). The PI type shows spreading of the carcinoma along the portal tracts with stricture of the central bile ducts and dilation of the peripheral bile ducts. The IG type presents as a papillary tumor within the dilated bile duct lumen. Some IG-type ICCs are considered to be an intraductal papillary neoplasm of the bile duct. This classification system provides useful information during surgery (Figure 1). For example, the efficacy of hilar resection is not emphasized except in the case of PI-type ICCs. This macroscopic classification cannot be applied to HCC. Therefore, studies focusing on the association of the macroscopic subtypes with biological behavior, clinical features, and radiologic findings are needed to establish the therapeutic strategy for ICC. Although the macroscopic features are prominent in ICCs, another aspect of ICCs, in which ICCs cannot be discussed independently of other primary liver cancers, exists. Recent histopathologic and immunohistochemical studies have reported that hepatic progenitor cells (HPC) or stem cells play important roles in liver carcinogenesis including both HCCs and ICCs, supporting the hypothesis that HCCs and ICCs share a common evolutionary origin[3,4]. In 2010, the World Health Organization (WHO) established a new classification system of combined hepatocellular-cholangiocarcinoma (cHCC-CC) based on the presence of stem-cell features[5]. According to this new system, cHCC-CCs are classified into two major subtypes, classic type and subtypes with stem-cell features. Subtypes with stem-cell features are further subclassified into three types: typical type, intermediate-cell type, and cholangiocellular type. In addition, recent reports showed that some cases of HCCs and ICCs are associated with hepatic stem cells. However, little is known about the clinical significance of stem cells in ICCs. This review summarizes recently published studies (from 2011 to 2013) covering various aspects of ICC and cHCC-CC, focusing especially on the macroscopic subtypes and stem-cell features.

Figure 1 Some intraductal growth-type intrahepatic cholangiocarcinomas are considered to be an intraductal papillary neoplasm of the bile duct, this classification system provides useful information during surgery. A: Gross feature of mass-forming (MF) + periductal infiltrating (PI)-type intrahepatic cholangiocarcinoma (ICC) obtained by left hepatectomy with bile duct resection. The carcinoma spreads along the hilar biliary tree (arrow) in communication with a white firm mass; B-D: Operative findings and resected specimens of MF + intraductal growth (IG)-type ICC. The common hepatic duct is incised, and the soft tumor comprising the intraductal components is easily removed (arrow) without infiltration to the ductal wall; C: Hepatic anterior segmentectomy is performed for MF components; D: IG components are composed of tan-colored soft tissues with necrosis.

CLINICAL STUDIES OF ICC

Recent clinical researches of ICC are summarized in Tables 1 and 2[6-24]. The association between macroscopic subtypes and survival rate and lymph node metastasis has been discussed ever since the macroscopic subtype was established. IG-type ICCs have a favorable outcome because this tumor type shows intraductal growth without invasiveness[2]. Of the three subtypes, MF+PI-type ICCs have the highest incidence of lymph node metastasis (50% to 73%)[15] and are associated with the lowest 5-year survival rate (0% to 19.4%). PI-type and MF-type have relatively favorable outcomes when lymph node metastasis or hilar invasion is absent.

Table 1 Clinical study of intrahepatic cholangiocarcinoma.

Ref.	n	Survival rate (%)	MST (mo)	Prognostic factor
Marubashi et al[6]	111	59.7 (3 yr)	-	IM, Hilar inv, LN
Guglielmi et al[7]	145	-	19 (LN+), 42 (LN-)	LNR > 0.25, LN
Zhu et al[8]	37	-	-	CA19-9, Low prealbmin
Dhanasekaran et al[9]	105	-	16	V
Wang et al[10]	367	-	-	CEA, CA19-9, Size, V
De Rose et al[11]	79 (MF)	-	-	Doubling time < 70 d
Sulpice et al[12]	87	-	-	BT, Maj, Size, V, IM
Ribero et al[13]	434	39.8 (5 yr)	-	LN, CA19-9, IM
Liu et al[14]	132	-	-	Por, CA19-9, Dis(-)
Uchiyama et al[15]	334	-	-	Shown in Table 2
Chen et al[16]	64	32 (3 yr)	-	LN, PN, Size
Uno et al[17]	273	-	-	Shown in Table 2
Morine et al[18]	22	-	-	Shown in Table 2
Jiang et al[19]	102	-	-	CA19-9, IM
Murakami et al[20]	44	47 (5 yr)	-	LN
Clark et al[21]	4893	8.4 (5 yr, LN+)	-	LN
		25 (5 yr, LN-)
de Jong et al[22]	449	31 (5 yr)	27	IM, V, LN
Li et al[23]	115	-	-	Cirrhosis
Chen et al[24]	320	-	-	-

MST: Median survival time; Prognostic factor: Factor for poor prognosis; IM: Multiple tumors or intrahepatic metastasis; Hilar inv: Hilar invasion; LN: Lymph node metastasis; LNR: Rate of the positive lymph node metastasis; CA19-9: Elevated serum carbohydrate antigen 19-9; CEA: Elevated serum carcinoembryonic antigen; Size: Larger tumor size; V: Vascular invasion; BT: Blood transfusion during operation; Dis: Lymph node dissection; PN: Perineural invasion.

Table 2 Clinical studies of intrahepatic cholangiocarcinoma focused on the macroscopic subtypes.

Ref.	n	Findings or conclusion
Uchiyama et al[15]	334	Lymph node metastasis: MF: 16%; IG: 0%; PI and MF + PI: 60%
		Survival rate (5 yr): MF: 26%; IG: 79.3%; PI and MF + PI: 19.4%
Uno et al[17]	273	Rate of PI-type: 7.9%
		The PI-type shows significantly better survival than MF- and MF + PI-type.
Morine et al[18]	22	The PI-type shows a lower incidence of intrahepatic metastasis
		Routine lymph node dissection do not improve survival in MF-type

MF: Mass-forming type; IG: Intraductal growth type; PI: Periductal infiltrative type

Figure 2 Case presentation of combined hepatocellular-cholangiocarcinoma. A: Preoperative computed tomography shows a large mass composed of two major components that replaces the lateral segment. The mass shows ringed enhancement in the delayed phase in the cephalad area and early enhancement with washout in the delayed phase in the caudal area. Intrahepatic metastases are observed in the S4 segment (arrow); B: Gross features of the resected specimen. Hepatocellular carcinoma (HCC) components are composed of tan-colored soft tissues. Cholangiocarcinoma (CC) components are composed of white firm tissues with central necrosis; C: Small round cells and fibrous stroma are observed at the boundary area between the HCC and CC components (blue flame in panel B).

Over the most recent 3 years, 19 studies have been published (Tables 1 and 2). Most of these studies describe the poor prognostic factors of resected cases of ICC. The most significant prognostic factor is lymph node metastasis. However, whether routine lymph node dissection improves postoperative survival is still unclear.

The literature on the macroscopic subtypes is very scant. Uchiyama et al[15] and Uno et al[17] reported that the PI type showed significantly better survival than the MF and MF+PI types, supporting the results of previous reports. The difference in malignant potential between each subtype emphasizes the importance of the preoperative identification of each subtype.

RADIOLOGIC STUDIES OF ICC

Table 3 summarizes recent radiologic studies of ICC[25-30]. The typical enhancement pattern of ICC on CT and MRI is that of ringed enhancement in the early phase with central delayed enhancement, reflecting the abundant fibrous stroma in ICC. However, Kim et al[26] reported that 6 (30%) of 20 ICCs appeared as hypervascular lesions with washout in the delayed phase, resembling HCCs. In addition, Ariizumi et al[29] pointed out that MF-type ICCs with hypervascular-type pattern had more favorable prognosis than those with the typical enhancement pattern. The histopathological characteristics of hypervascular-type ICCs have not been clarified. Cholangiocellular carcinoma (CoCC), a subtype of ICC, has been reported to originate from the ductules, or canals of Hering, and appears as a hypervascular mass similar to HCC[31]. These results of recent radiologic studies suggest the possibility that some ICCs share the same origin with that of CoCC, i.e., HPCs. Especially in MF-type ICCs, comparative studies between the enhancement patterns and histopathologic findings are needed for further exploration. However, these descriptions can be applied to only MF-type ICCs. Xu et al[28] reported the difference of enhancement patterns on contrast-enhanced ultrasonography between each subtype and demonstrated that most IG-type ICCs appeared as a mass showing homogenous hyperenhancement. This finding provides useful knowledge for preoperative differentiation between IG-type and PI-type ICC.

Table 3 Radiologic studies of intrahepatic cholangiocarcinoma.

Ref.	n	Method	Findings or conclusion
Nanashima et al[25]	42	CT	Factor for poor prognosis: case showing arterial enhancement with lower attenuation
Kim et al[26]	20	MRI	6 (30%) of the 20 cases appeared as hypervascular lesions with washout on delayed phase
Kang et al[27]	50	MRI	Percentage of relative enhancement on hepatobiliary phase was significantly higher in moderately differentiated tumors than in poorly differentiated tumors and in patients without than in those with lymph node metastasis
Xu et al[28]	40	Contrast enhanced ultrasono-graphy	MF-type (n = 32): (1) peripheral rim-like hyperenhancement (n = 19); (2) heterogenous enhancement (n = 10); and (3) homogenous hyperenhancement (n = 3)
Ariizumi et al[29]	26	FDG PET	PI-type (n = 4): heterogenous enhancement (n = 4) IG-type (n = 4): (1) homogenous hyperenhancement (n = 3); and (2) heterogenous enhancement (n = 1) FDG PET was able to predict patient outcome after radioembolization treatment

CT: Computed tomography; MRI: Magnetic resonance imaging; FDG PET: ¹⁸F-fluorodeoxy glucose positron emission tomography.

PATHOBIOLOGICAL STUDIES OF ICCs

During the most recent 3 years, many molecules have been identified as biomarkers for poor prognosis of ICCs (Tables 4-6)[31-71]. Among these, researchers have paid close attention to molecules associated with epithelial-mesenchymal transition (EMT)[32,38,53,55]. The close association between EMT and the progression of ICC was confirmed not only by immunohistochemistry but also by functional and comprehensive analyses. The fact that EMT induces progression of ICC led us to hypothesize that abundant fibrous stroma in ICCs play an important role in the invasive growth and metastasis of this cancer. In addition, Oishi et al[53] reported that activation of miR-200c induced a reduction in EMT and in the expression of neural adhesion molecule (NCAM). Given that NCAM is known to be a hepatic progenitor cell marker, a hypothesis that the hepatic progenitor cell markers and molecules associated with EMT are regulated by common upstream molecules can be proposed. Further functional analyses are needed to confirm this hypothesis.

Table 4 Pathobiological studies of intrahepatic cholangiocarcinoma.

Ref.	n	Method	Target	Conclusion
Gu et al[32]	85	IHC	E-cadherin	(-)por
			Beta-catenin	(-)por
			Vimentin	(-)por
Yan et al[33]	49	IHC	Smad4	(-)por, advanced stage, LN
Kamphues et al[34]	65	DNA-Cyto	DNA-index	(+)poor prognosis
Mano et al[35]	132	IHC	Roundabout-1	(-)Size, Ki67index, poor prognosis
			Slit-1	(-)PN, LN
Yin et al[36]	411	Serum	γ-glutamyl transferase	(+)V, LN, poor prognosis,
				incomplete encapsulation
Sulpice et al[37]	40	mRNA	Osteopontin	(+)poor prognosis
		(Stroma)	TGFβ2	(+)poor prognosis
			Laminin	(+)poor prognosis
Zhou et al[38]	Cell	mRNA	Notch-1	(+)EMT
	line	Western
Li et al[39]	173	IHC	CKAP4	(+)favorable prognosis
Nanashima et al[40]	38	IHC	CD44	(+)PI-type, poor prognosis
			Gli1	(+)poor prognosis
Nutthasirikul et al[41]	-	mRNA	Δ133p53/TA	(+)poor prognosis
			P53
	-	IHC	Mutantp53	(+)poor prognosis
Zhang et al[42]	33	mRNA	Capn4	(+)LN, advanced stage,
		Western		Poor prognosis
Ding et al[43]	20	IHC	Integrinα6	(+)IM, Size, V, poor prognosis
		Cell	Integrinα6	(-)decrease of metastasis
Aishima et al[44]	134	IHC	Cox-2	(+)poor prognosis, LN
			iNOS	(-) LN
Chen et al[45]	61	IHC	IMP3	(+)Por, advanced stage, V
				poor prognosis, CA19-9

IHC: Immunohistochemistry; mRNA: Real-time polymerase chain reaction; Western: Western blotting; DNA-cyto: DNA image cytometry; Cell: Functional analyses using cell lines; CKAP4: Cytoskeleton-associated protein4; iNOS: Inducible nitric oxide synthase; IMP3: Insulin-like growth factor II mRNA binding protein.

Table 5 Pathobiological studies of intrahepatic cholangiocarcinoma 2.

Ref.	n	Method	Target	Conclusion
Shi et al[46]	138	IHC	DKK-1	(+)poor prognosis
				elevated sMMP9 and VEGF-C
		Cell	DKK-1	(-)decrease in cell migration and invasiveness
				(+)LN, Por, advanced stage, V
Yao et al[47]	96	IHC	Vimentin	poor prognosis
			and
			N-cadherin	(+)MF-type
Zhou et al[48]	54	IHC	HBx-protein	well differentiated tumor
				(+)well differentiated tumor, IG-type
Choi et al[49]	46	IHC	CK20	(+)favorable prognosis
			MUC6	(+)Size, LN, V, advanced stage
Jeong et al[50]	43	IHC	FABP-5	(-)decrease in cell proliferation and
		Cell	FABP-5	invasion
				(+)elevated serum CEA and CA
Tsai et al[51]	112	IHC	S100P	19-9 value, MUC2 positive
				poor prognosis
				(+)perineural invasion
	86	Sequencing	K-ras mutation	poor prognosis
			miR-200c	(+)reduction of EMT
Oishi et al[53]	-	Microarray		reduction of NCAM1 expression
			HCV core	(+)enhanced NFAT expression
Liao et al[54]	-	Cell	protein	(+)enhanced Angiotensin II receptor expression and fibrogenesis of
			Angiotensin	cancerous stroma, metastasis
Okamoto et al[55]	-	Cell	II and SDF1

DKK1: Dickkopf-related protein1; MMP: Matrix metalloproteinase; FABP-5: Fatty acid-binding protein 5; SDF1: Stromal cell derived factor 1; NCAM1: Neural cell adhesion molecule1; EMT: Epithelial mesenchymal transition; NFAT1: Nuclear factor of activated T-cells.

Table 6 Pathobiological studies of intrahepatic cholangiocarcinoma 3.

Source	n	Method	Target	Conclusion
Li et al[56]	-	Tissues	miR-214	(-)increased expression of Twist(EMT
				-associated gene)
Gu et al[57]	123	IHC	IL-17cells	(+)poor prognosis
			(intratumoral)
Higashi et al[58]	63	IHC	MUC16	(+)poor prognosis
Gu et al[59]	83	IHC	E-cadherin	(-)poor prognosis
			Beta-catenin	(-)V
			EGFR	(+)Por
Wang et al[60]	77	IHC	P-70S6K	(+)Por
			4EBP1	(+)poor prognosis
Hirashita et al[61]	35	IHC	MMP-7	(+)poor prognosis
Srimunta et al[62]	55	IHC	ABCC-1	(+)poor prognosis
Morine et al[63]	35	IHC	HDAC	(+)advanced stage, LN
				poor prognosis
Wakai et al[64]	34	IHC	RRM1	(+)gemcitabine resistance
Larbcharoensub et al[65]	60	IHC	ABCG2	(-)poor prognosis, LN, Por
Lee et al[66]	101	IHC	PTEN	(+)favorable prognosis
			P-AKT1	(+)favorable prognosis
			P-MTOR	(+)favorable prognosis
Dong et al[67]	108	IHC	Beclin1	(-)LN, poor prognosis
Shinozaki et al[68]	83	IHC	Claudin-18	(+)LN, PI-type, perineural invasion
Wakai et al[69]	34	IHC	NQO1	(-)Por, poor prognosis
Aishima et al[70]	110	IHC	S100P	(+)PI-type
			S100P(nuc)	(+)LN, V
Zhou et al[71]	89	IHC	MAGE3/4	(+)larger tumor size, poor prognosis

EGFR: Epidermal growth factor receptor; P-70S6K: P70 ribosomal protein S6 kinase; 4EBP1: 4E-binding protein-1; ABCC-1: Adenosine triphosphate binding cassette C1; HDAC: Histone deacetylase; RRM1: Ribonucleotide reductase-M1; ABCG2: Adenosine 5’ triphosphate-binding cassetteG2; PTEN: Phosphatase and tensin homolog on chromosome ten; PAKT: Phosphorylated Akt; PMTOR: Phosphorylated MTOR; NQO1: Quinine oxidoredactase; MAGE: Melanoma antigen.

The literature on the association between macroscopic subtypes and the expression of genes are very scant[48,49,68,70], similar to that in the clinical study literature. Shinozaki et al[68] reported that claudin-18 (CLDN18), a tight junction protein specific to the stomach and lung, is highly expressed in precancerous lesions of biliary intraepithelial neoplasms and PI components of ICCs. CLDN18 has been reported to be expressed in various gastrointestinal cancer tissues and to be associated with morphogenesis of the histologic subtype and the specific mucin phenotype[72]. In addition, we previously reported the association between the expression of CLDN18 and intestinal-type differentiation in intraductal papillary-mucinous neoplasm of the pancreas[73]. Thus, there is considerable interest in the crucial role of CLDN18 in the development of PI-type morphology in ICCs.

RECENT RESEARCH ON cHCC-CC

There is a large dissociation in the postoperative survival rates of cHCC-CC reported in the recent researches[74-90] (Tables 7-9), probably because the case numbers are limited. In addition, cHCC-CC is associated with many factors that contribute to poor prognosis including lymph node metastasis, higher levels of serum AFP, and portal vein thrombosis, reflecting intermediate features of cHCC-CC between HCC and ICC (Figure 2). The intermingling of findings of cHCC-CCs are also demonstrated by radiologic studies. Based on the new WHO classification system of cHCC-CC, some immunohistochemical research highlighting the expression of HPC markers has been published in the past 3 years in which YAP1 and EpiCAM, are reported to be markers of poor prognosis. These molecules are mainly distributed across the intermediate- and cholangiocellular-type components. Kim et al[85] reported that YAP1 is localized in the transitional zone between HCC and ICC components. In addition, Akiba et al[87] demonstrated that vimentin is strongly expressed in intermediate-type cHCC-CC. Similar to their role in ICCs, HPC markers may also play a crucial role in the progression of cHCC-CC through EMT. These components may harbor biological instability resembling undifferentiated carcinoma that leads to invasive behavior. However, CoCC, a subtype of ICC, has been known to be a tumor with characteristics resembling those of HCC and to have a relatively favorable prognosis (Figure 3). Given that CoCC is also derived from HPCs[31], a contradictory point exists with regard to the role of HPCs in the progression of ICCs and cHCC-CCs. We speculate that each HPC marker performs various functions involving progression and metastasis of ICCs and cHCC-CCs to a lesser or greater extent.

Figure 3 Resected case of cholangiocellular carcinoma. A: Computed tomography (CT) reveals a mass showing ringed enhancement with portal venous penetration; B: CT findings reflect the non-infiltrative growth of the tumor to the portal tract; C: Histopathologically, the size of the carcinoma cells is small, with the cells forming anastomosing patterns with abundant fibrous stroma.

Table 7 Clinical studies of combined hepatocellular-cholangiocarcinoma.

Source	n	Conclusion or findings
Yap et al[74]	11	Survival rate: 69.3% (3 yr)
Lee et al[75]	65	(1) The clinical characteristics of cHCC-CC are similar to those of HCC
		(2) Overall survival of cHCC-CC is similar to that of ICC
Yin et al[76]	113	(1) Findings similar to HCC: infection with hepatitis virus; presence of cirrhosis; elevated AFP levels
		(2) Findings similar to ICC: serum CA19-9 elevation; incomplete capsules; lymph node involvement
		(3) Survival rate: 41.4%(3 yr); 36.4% (5 yr)
		(4) Factors for poor prognosis: radical liver resection
Ariizumi et al[77]	44	(1) Survival rate: 24%
		(2) Median survival time: 15.4 mo
Yu et al[78]	14	(1) Clinical characteristics: hepatitis B virus infection: 13/14;
		elevated AFP levels: 11/14
		(2) Median survival time: 7.9 mo
		(3) Stem cell markers (IHC): c-Kit 71.4%; CD90: 85.7%; CD133: 92.9%; CK19: 78.6%
Park et al[79]	21	Factor for poor prognosis: serum AFP levels
Park et al[80]	43	(1) median survival time: 34 mo
		(2) Survival rate: 18.1% (5 yr)
		(3) Factors for poor prognosis: Portal vein thrombosis; distant metastasis
Zhan et al[81]	27	(1) CK-7: 86.4%; CK19: 90.9%
		(2) Survival rate: 49.4%
		(3) Factors for higher recurrence: lymph node metastasis

AFP: Alpha-fetoprotein.

Table 8 Radiologic studies of combined hepatocellular-cholangiocarcinoma.

Ref.	n	Methods	Conclusion or findings
Ijichi et al[82]	3	FDG	(1) SUVmax value of three cHCC-CC cases: 9.9, 12.0, and 13
		-PET	(2) Median SUVmax value of poorly differentiated HCC: 5.7
			(1) 6/11 showed early ring enhancement with progressive enhancement in central portion.
			(2) 5/11 showed a diffuse heterogenous early enhancement.
de Campos et al[83]	11	MRI	Characteristics findings of cHCC-CC: irregular shape and strong rim enhancement during early phase; absence of target appearance on hepatobiliary-phase
Hwang et al[84]	20	MRI

cHCC-CC: Combined hepatocellular-cholangiocarcinoma; MRI: Magnetic resonance imaging; FDG-PET: ¹⁸F-fluorodeoxy glucose positron emission tomography.

Table 9 Pathobiological studies of combined hepatocellular-cholangiocarcinoma.

Ref.	n	Method	Target	Conclusion
Kim et al[85]	58	IHC	YAP1	(+): transition zone, poor prognosis
			EpiCAM	(-)favorable prognosis
			CK19	(-)favorable prognosis
Ikeda et al[86]	36	IHC	DLK1	(+)poor prognosis
Akiba et al[87]	54	IHC	CD56	(+): components apart from HCC
			c-Kit	(+): components apart from HCC
			EpiCAM	(+): components apart from HCC
			CD133	(+): intermediate type or cholangiolocellular type
			Vimentin	(+): intermediate type or cholangiolocellular type
Coulouarn et al[88]	152	Microarray	-	(1) TGFbeta and beta-catenin are identified as the two major signals in the progression of cHCC-CC/
				(2) cHCC-CC shares the characteristics of poorly differentiated HCC.
				(+)poor prognosis
				Both HCC and CC components of most
				Of the cHCC-CC express both AFP and
Cai et al[89]	80	IHC	PCNA	CK19
Itoyama et al[90]	20	IHC	AFP and
			CK19

cHCC-CC: Combined hepatocellular-cholangiocarcinoma; YAP1: Yes-associated protein 1; EpiCAM: Epithelial cell adhesion molecule; DLK1: Delta-like 1 homolog; PCNA: Proliferating cell nuclear antigen index in nontumor ductular reaction.

CONCLUSION

Recent research in ICC has revealed that each tumor shows different clinical and radiologic characteristics between the macroscopic subtypes. However, there are still many unclear points regarding the molecular mechanisms yielding these subtypes. It is of particular interest to identify the molecular markers inducing invasion, metastasis, and the macroscopic growth patterns of ICC. Many researchers have noted that HPC markers and EMT are involved in the progression of ICCs. Because most cHCC-CCs show MF-type morphology, we infer that HPC markers are closely associated with the morphogenesis and histogenesis of MF-type ICCs. Therefore, studies of ICC, and especially of its molecular pathology, should be designed in conjunction with those of cHCC-CC.