FGFR2 fusions assessed by NGS, FISH, and immunohistochemistry in intrahepatic cholangiocarcinoma.

Background: FGFR2 fusion has become a promising therapeutic target in iCCAs; however, the procedure for screening FGFR2 fusion has not been conventionally developed.

Methods: FGFR2 fusion was identified using DNA + RNA-based NGS and FISH, and the concordance between DNA + RNA-based NGS, FISH, and IHC was compared.

Results: FGFR2 fusions were detected in 9 out of 76 iCCAs (11.8%). The consistency of FISH and DNA + RNA-based NGS for FGFR2 fusions was high (κ value = 0.867, P = 0.001), while the consistency of IHC and DNA + RNA-based NGS was lower (κ value = 0.464, P = 0.072). All nine FGFR2 fusion-positive iCCAs were MSS with a median TMB of 2.1 mut/Mb, and only one had a CPS (PD-L1) above 5. Two FGFR2 fusion-positive iCCA patients were treated with and benefited from FGFR inhibitor therapy.

Conclusions: FGFR2 fusion should be assessed for advanced iCCA patients. We recommend DNA + RNA-based NGS as the preferred option to supply all possible therapeutic targets. FISH should be preferred if the tumor sample is insufficient for NGS or if the patient is inclined to receive FGFR inhibitors promptly. Although IHC is not the preferred method to identify FGFR2 fusion, it might be used as preliminary screening for FGFR2 alterations if the hospital cannot offer NGS or FISH, and the results need to be validated before FGFR2 inhibitors treatment.