Genetic alterations including fusions in fibroblast growth factor receptor 2 (FGFR2) are detected in 10-20% of intrahepatic cholangiocarcinoma (iCCA), and FGFR2 inhibitors are effective for the treatment of iCCA. We examined a prevalence of FGFR2 genetic alterations and their clinicopathological significance in combined hepatocellular-cholangiocarcinoma (cHCC-CCA). FGFR2 expression, which is a surrogate marker for FGFR2 genetic alterations, was immunohistochemically assessed in the liver sections from 75 patients with cHCC-CCA, 35 with small duct-type iCCA, 30 with large duct-type iCCA, and 35 with hepatocellular carcinoma (HCC). FGFR2 genetic alterations were detected by reverse transcription-PCR and direct sequence. An association of FGFR2 expression with clinicopathological features was investigated in cHCC-CCAs. FGFR2 expression was detected in significantly more patients with cHCC-CCA (21.3%) and small duct-type iCCA (25.7%), compared to those with large duct-type iCCA (3.3%) and HCC (0%) (p < 0.05). FGFR2-positive cHCC-CCAs were significantly smaller size (p < 0.05), with more predominant cholangiolocarcinoma component (p < 0.01) and less nestin expression (p < 0.05). Genetic alterations of ARID1A and BAP1 and multiple genes were significantly more frequent in FGFR2-positive cHCC-CCAs (p < 0.05). 5\'/3\' imbalance in FGFR2 genes indicating exon18-truncated FGFR2 was significantly more frequently detected in FGFR2-positive cHCC-CCAs and small duct iCCAs, compared to FGFR2-negative ones (p < 0.05). FGFR2::BICC fusion was detected in a case of cHCC-CCAs. FGFR2 genetic alterations may be prevalent in cHCC-CCAs as well as small duct-type iCCAs, which suggest cHCC-CCAs may also be a possible therapeutic target of FGFR2 inhibitors.

OBJECTIVE: Intrahepatic cholangiocarcinoma (iCCA) is subclassified into small and large duct types. These two subtypes show distinct differences in various clinicopathological features and possible cell origin and pathways of carcinogenesis, however, a differential diagnosis may be sometimes difficult. Given the type IV intermediate filament, Nestin, may be a candidate diagnostic marker for combined hepatocellular-cholangiocarcinoma (cHCC-CCA) and small duct type iCCAs, the significance of nestin as a differential diagnostic marker between small and large duct types of iCCAs was addressed in the present study.
METHODS: Nestin expression was immunohistochemically assessed in the sections from 36 patients with small duct-type iCCA, 30 with large duct-type iCCA, and 27 with extrahepatic cholangiocarcinoma (CCA). Nestin expression and its relationship with clinicopathological features and genetic alterations were investigated in small duct type iCCAs.
RESULTS: Nestin expression was detected in 17 small duct type iCCAs (47.2%), one large duct type iCCA (3.8%) and zero extrahepatic CCA. Nestin expression was significantly more frequent in the patients with small duct type iCCAs than in those with large duct type iCCA and extrahepatic CCA (p < 0.01). In 10 liver biopsies, all samples with nestin expression were small duct type iCCAs. Nestin-positive small duct type iCCAs were characterized by a higher histological grade, compared to Nestin-negative small duct type iCCAs (p < 0.01). Nestin-positive small duct type iCCAs tended to have 2 or more genetic alterations, but there was no statistic difference (p > 0.05).
CONCLUSIONS: Different nestin expression may reflect differences between small duct type iCCA and large duct type/extrahepatic CCA and may be a useful diagnostic marker for small duct type iCCAs.