Stemness characteristics of fibrolamellar hepatocellular carcinoma: immunohistochemical analysis with comparisons to conventional hepatocellular carcinoma.

The involvement of cancer stem cells (CSC) in tumorigenesis has been studied in several malignancies, but their presence in fibrolamellar hepatocellular carcinoma (FLHCC) has not previously been evaluated. General characteristics of "stemness" include the expression of putative stem cell antigens, reduced cell cycle progression, and limited functional differentiation or dedifferentiation under the influence of the microenvironment. Immunohistochemical probes applied to 8 archival cases of FLHCC vis-à-vis contiguous non-neoplastic parenchyma, which was present in 5 cases, revealed such stemness characteristics by showing: (a) stem cell antigens, with moderate to intense expression of CD133 in the cytoplasm (6 of 8 FLHCC cases and comprising >40% of the tumoral areas) and of CD44 on the plasmalemmal aspect (7 of 8 FLHCC cases and comprising 50 to 95% of the tumor cells), vs foci of such overexpressions in only 1 of 5 of the contiguous liver parenchyma (p = 0.053 and p = 0.015, respectively); (b) limited G1 to S phase progression ( <1 % of tumor cells with nuclear S phase kinase-associated protein [Skp]2 expression); and (c) dedifferentiation or reduced functional differentiation in the form of minimal to absent expression of a differentiation-associated marker, peroxisomal proliferator-activator receptor (PPAR)-gamma in tumoral nuclei and loss of plasmalemmal expression of beta-catenin in 6 of 8 FLHCC cases vs expression of these proteins in the non-neoplastic, differentiated hepatocytes in 5 of 5 and 4 of 5 cases, respectively, in contiguous liver parenchyma (p <0.01 and p = 0.053, respectively). In contrast, only 1 of 11 cases of well-differentiated, conventional hepatocellular carcinoma (HCC) showed mild to moderate expression of CD133 in the cytoplasm, but with the majority (8 of 11) showing occasional nuclear expression. Similarly, only 3 of 11 cases of conventional HCC expressed plasmalemmal CD44. Notably, 11 of 11 cases of conventional HCC expressed beta-catenin on the plasmalemmal aspect of the tumor cells, and 3 of 11 showed nuclear translocation. These findings in conventional HCC were significantly different from those in FLHCC (p = 0.003, 0.009, and 0.0005, respectively). This study provides evidence of stemness in FLHCC and discusses the implications of stemness in the histogenesis of FLHCC vs conventional, well-differentiated HCC.