Low-level clonal FGFR2 amplification defines a unique molecular subtype of intrahepatic cholangiocarcinoma in a Chinese population

Intrahepatic cholangiocarcinoma (ICC) is a subtype of primary liver cancer rarely curable by surgery that is increasing rapidly in incidence. Chromosomal translocations and amplifications of the fibroblast growth factor receptor 2 (FGFR2) locus are present in several kinds of tumors including ICC, but their incidence has not been assessed in Chinese patients. Using break-apart probes and by determining the ratios of FGFR2/chromosome enumeration probe (CEP) 10 double-color probes, we evaluated 122 ICCs for the presence of FGFR2 translocations and amplifications, respectively, by fluorescence in situ hybridization. We further determined FGFR2 protein expression by immunohistochemistry and analyzed the clinicopathologic records of the patients. Eight tumors (6.6%) had FGFR2 translocations, whereas 15 (12.3%) had low-level FGFR2 amplification. Interestingly, the tumors that showed both translocation and low-level amplification frequently were of the mass-forming type. Compared with the ICCs with normal FGFR2s, tumors with amplifications secreted less mucus (P = .017) and typically were accompanied by hepatitis B virus infection (P = .004). Tumors with low-level amplification generally were of lower stage (P = .013) and associated with better overall survival (P = .017). As tumors with FGFR2 amplification exhibit different biology from lesions with a normal gene, low-level amplification of FGFR2 may play an important role in tumor progression and may be a marker for targeted therapy.