Landscape of Clinical Resistance Mechanisms to FGFR Inhibitors in FGFR2-Altered Cholangiocarcinoma

Purpose: FGFR inhibitors have shown efficacy in treating FGFR2-altered cholangiocarcinoma, leading to the approval of reversible inhibitors like pemigatinib and infigratinib, as well as the irreversible inhibitor futibatinib. However, the development of acquired resistance limits their clinical effectiveness. Some resistance mechanisms, including secondary mutations in the FGFR2 kinase domain, have been identified. In this study, we aimed to explore the landscape of acquired resistance to FGFR inhibition and validate these findings in model systems.

Experimental Design: We analyzed acquired resistance mechanisms in circulating tumor DNA or tumor tissue samples from 82 FGFR2-altered cholangiocarcinoma patients who progressed after FGFR inhibitor therapy, as reported in 12 published studies. Functional assays were performed to evaluate candidate resistance alterations.

Results: Among the 82 patients, 49 (60%) had one or more secondary FGFR2 kinase domain mutations associated with acquired resistance. The most common mutations were N550 (molecular brake) and V565 (gatekeeper), accounting for 63% and 47% of all FGFR2 kinase domain mutations, respectively. Functional assays demonstrated that different inhibitors had distinct activity profiles against these mutations. Notably, disruption of the cysteine residue covalently bound by futibatinib (FGFR2 C492) was rare, occurring in only 1 out of 42 patients treated with this drug. FGFR2 C492 mutations were resistant to futibatinib but exhibited reduced signaling activity, which may explain their infrequent occurrence.

Conclusions: These findings confirm that secondary FGFR2 kinase domain mutations, particularly N550 and V565, are the primary mechanisms of acquired resistance to FGFR inhibitors. This highlights the need for the development of combination therapies and next-generation FGFR inhibitors that can target a broader TAS-120 range of FGFR2 resistance mutations.