Distinct Clinicopathologic and Genetic Features of 2 Histologic Subtypes of Intrahepatic Cholangiocarcinoma.

Previous studies have identified 2 clinically significant morphologic subtypes of intrahepatic cholangiocarcinoma (ICC) on the basis of anatomic location and/or histologic appearances. Recognizing that these classification schemes are not always applicable practically, this study aimed to establish a novel classification system based on mucin productivity and immunophenotype and to determine the rationale of this classification by examining the clinicopathologic and genetic characteristics of the 2 subtypes defined by this method. We retrospectively investigated 102 consecutive ICC cases and classified them on the basis of mucin productivity and immunophenotype (S100P, N-cadherin, and NCAM). We found that 42 and 56 cases were classified as type 1 and type 2 ICCs, respectively, and only 4 cases were of indeterminate type. Type 1 ICC, generally characterized by mucin production and diffuse immunoreactivity to S100P, arose less frequently in chronic liver diseases and showed higher levels of serum CEA and CA 19-9 than did type 2 ICC, which generally showed little mucin production and exhibited immunoreactivity to N-cadherin and/or NCAM. Type 1 ICC was characterized by several pathologic features, including higher frequencies of perineural invasion and lymph node metastasis. Although the log-rank test demonstrated that type 1 ICC had significantly worse survival, the multivariate Cox regression analysis showed no prognostic significance of this histologic subtype. Genetic analyses revealed that KRAS mutation was significantly more frequent in type 1 ICC, whereas IDH mutation and FGFR2 translocation were restricted to type 2 ICC. In conclusion, the present classification of ICC based on mucin productivity and immunophenotype identified 2 subtypes with clinicopathologic significance.