A Robust FISH Assay to Detect FGFR2 Translocations in Intrahepatic Cholangiocarcinoma Patients

FGFR fusions retaining the FGFR kinase domain are active kinases that are either overexpressed or constitutively activated throughout diverse cancer types. The presence of FGFR translocations enhances tumor cell proliferation and contributes to significant sensitivity to FGFR kinase inhibitors. FGFR2 as an actionable target in intrahepatic cholangiocarcinoma (iCCA) has been tested in many clinical trials. FISH (fluorescence in situ hybridization) and NGS (next-generation sequence) are well-known tools to investigate the translocations of FGFR with multiple or unknown translocation partners. A rapid and robust FISH assay was developed and validated to detect FGFR2 translocations from FFPE specimens in iCCA. The analytical performance of the FISH assay was evaluated for probe localization, probe sensitivity and specificity, and assay precision. Twenty-five archival FFPE specimens from local iCCA patients were tested for FGFR2 translocations. FISH results were correlated with that of NGS on some samples. Biallelic translocations and a novel FGFR2 translocation involving the partner gene, SHROOM3, t(4;10) (q21;q26), were identified in a local iCCA patient.