Oncogenic activation revealed by FGFR2 genetic alterations in intrahepatic cholangiocarcinomas.

BACKGROUND: Except for gene fusions, FGFR2 genetic alterations in intrahepatic cholangiocarcinomas (ICCs) have received limited attention, leaving patients harboring activating FGFR2 gene mutations with inadequate access to targeted therapies. EXPERIMENTAL DESIGN: We sought to survey FGFR2 genetic alterations in ICC and pan-cancers using fluorescence in situ hybridization and next-generation sequencing. We conducted an analysis of the clinical and pathological features of ICCs with different FGFR2 alterations, compared FGFR2 lesion spectrum through public databases and multicenter data, and performed cellular experiments to investigate the oncogenic potential of different FGFR2 mutants. RESULTS: FGFR2 gene fusions were identified in 30 out of 474 ICC samples, while five FGFR2 genetic alterations aside from fusion were present in 290 ICCs. The tumors containing FGFR2 translocations exhibited unique features, which we designated as the "FGFR2 fusion subtypes of ICC". Molecular analysis revealed that FGFR2 fusions were not mutually exclusive with other oncogenic driver genes/mutations, whereas FGFR2 in-frame deletions and site mutations often co-occurred with TP53 mutations. Multicenter and pan-cancer studies demonstrated that FGFR2 in-frame deletions were more prevalent in ICCs (0.62%) than in other cancers, and were not limited to the extracellular domain. We selected representative FGFR2 genetic alterations, including in-frame deletions, point mutations, and frameshift mutations, to analyze their oncogenic activity and responsiveness to targeted drugs. Cellular experiments revealed that different FGFR2 genetic alterations promoted ICC tumor growth, invasion, and metastasis but responded differently to FGFR-selective small molecule kinase inhibitors (SMKIs). CONCLUSIONS: FGFR2 oncogenic alterations have different clinicopathological features and respond differently to SMKIs.