Table 1. Histological subtypes and pathological characteristics of iCCA.

Histological subtype	Large duct type iCCA	Small duct type iCCA
Gross pattern	Peritubular infiltrating pattern, mixed pattern	Mass forming pattern
Cell morphology	Columnar-cuboidal	Cuboidal-low columnar
Tissue structure	Irregular large ductal or tubular adenocarcinoma	Dense small ductal adenocarcinoma
Invasiveness	++ – +++	– –+
Mucus staining	++ – +++	– –+
Immunohistochemistry	S100P, MUC5AC, MUC6, TFF1	CRP, N-cadherin, CD56
Genetic variation	KRAS gene mutation	IDH1/2 gene mutation, FGFR2 gene fusion/rearrangement

iCCA, intrahepatic cholangiocarcinoma; S100P, S100 calcium-binding protein P; MUC, mucin; TFF, trefoil factor 1; CRP, C-reactive protein; CD56, cluster of differentiation 56.