Genomic correlates of response and resistance to the irreversible FGFR1-4 inhibitor futibatinib based on biopsy and circulating tumor DNA profiling.

Background: Futibatinib is the only covalent inhibitor of FGFR1-4 to gain regulatory approval in oncology. In this article, we present genomic analyses of tissue biopsies and circulating tumor DNA (ctDNA) from patients with 1 of nearly 20 tumor types treated with futibatinib in the phase I/II FOENIX study.

Patients and methods: Eligible patients included those with ctDNA samples collected per protocol at baseline and/or progression on futibatinib in the phase Ib portion of the study for FGF/FGFR-altered advanced solid tumors or the phase II portion of the study for FGFR2 fusion/rearrangement-positive cholangiocarcinoma. Assessments included analytical concordance between tumor and ctDNA analyses for detection of FGFR alterations, association of ctDNA-detected co-occurring genomic alterations with response to futibatinib, and determination of patterns of acquired resistance following progression on futibatinib.

Results: Among 300 patients treated with futibatinib, 226 were eligible for this analysis, including 139 (62%) with cholangiocarcinoma. Among patients with known FGFR2 fusions/rearrangements, FGFR1 fusions, FGFR3 fusions, or FGFR2 amplifications per tissue analysis, detection rates in ctDNA for these aberrations were 84%, 0%, 11%, and 59%, respectively. Objective response rates on futibatinib were not significantly different between patients with TP53-altered versus -unaltered solid tumors; progression-free survival was reduced in patients with CDKN2B-altered versus -unaltered cholangiocarcinoma (median 4.8 versus 11.0 months; P = 0.03). Acquired resistance to futibatinib was frequently polyclonal and driven by an array of mutations within the relevant FGFR kinase domain, predominantly V565L, V565F, and N550K variants.

Conclusions: In this largest and most systematic analysis of acquired resistance to an FGFR inhibitor from prospective clinical trials, emergence of secondary FGFR2 kinase domain mutations was observed in most patients receiving clinical benefit to futibatinib. ctDNA analysis shows clinically relevant potential as a noninvasive method for assessing genomic profiles, identifying patients who may benefit from FGFR inhibitor treatment, and exploring acquired resistance mechanisms.