Abstract 2618: Convergent MAPK pathway alterations mediate acquired resistance to FGFR inhibitors in cholangiocarcinoma with FGFR fusions/rearrangements (2022)

Abstract Purpose: Genomic aberrations in fibroblast growth factor receptor (FGFR) are oncogenic drivers in several cancers. FGFR inhibitors (FGFRi) have demonstrated antitumor activity in cholangiocarcinoma (CCA) with FGFR2 fusions/rearrangements, though acquired resistance remains a therapeutic challenge and has been linked to FGFR2 mutations other than fusions/rearrangements. We sought to investigate mechanisms of acquired resistance to FGFRi and approaches to overcome resistance. Methods: Longitudinal plasma samples were collected from patients with FGFR pathway alterations enrolled in the futibatinib phase I trial (NCT02052778) and sequenced using a targeted, 73-gene panel. A separate retrospective analysis was conducted to evaluate possible evolution of genomic aberrations in CCA patients with FGFR2 fusion/rearrangement who had additional tumor and/or plasma next-generation sequencing (NGS) following FGFRi therapy. To assess the efficacy of futibatinib in cells with FGFR2 fusions in vitro, a FGFR2-BICC1 fusion H69 cholangiocyte cell line was developed. MAPK pathway alterations (BRAF_V600E or KRAS_G12D) were introduced to determine the impact of these co-alterations on FGFRi sensitivity, and combinations were tested to determine if efficacy could be enhanced. Cell viability assays, colony formation assays, and western blots were utilized to determine the effects of these agents in engineered cells. Results: A total of 58 plasma samples were collected from 17 patients with FGFR pathway alterations who were enrolled in the futibatinib phase I trial, including 13 (76.5%) of which had CCA. One patient with a FGFR2-CTNNA3 fusion who had NRAS G12D and BRAF A694T at baseline which were undetected during treatment had a dramatic increase in their variant allele frequency (VAF) upon progression (4.2%-0.0%-100% and 2.8%-0.0%-50.9%, respectively). Further, additional MAPK alterations were detected at time of progression, including BRAF V600E, NRAS Q61K, NRAS G12C, NRAS G13D and KRAS G12K mutations. In our separate retrospective series, of 17 patients who underwent repeat tumor and/or plasma NGS following treatment with one or more FGFRi, 10 (58.8%) had newly detectable alterations in MAPK pathway genes, 10 (58.8%) had new FGFR2 alterations, and 7 (41.2%) developed new alterations in both FGFR2 and MAPK pathway genes. In vitro studies demonstrated that in isogenic H69 biliary cell lines, introduction of FGFR2-BICC1 robustly sensitized to FGFRi when compared to a parental cell line, which was blunted by the introduction of secondary KRAS_G12D or BRAF_V600E mutations. Conclusions: Convergent genomic evolution in the MAPK pathway may be a potential mechanism of acquired resistance to FGFRi therapy. Work is ongoing to determine if targeting co-alterations may enhance the efficacy of FGFRi in FGFR2-fusion driven malignancies. Citation Format: TImothy P. DiPeri, Ming Zhao, Tyler Moss, Michael Kahle, Payal Rauli, Sunyoung S. Lee, Abdel Halim, Hiroshi Hirai, Volker Wacheck, Karim Benhadji, Jordi Rodon, Milind Javle, Funda Meric-Bernstam. Convergent MAPK pathway alterations mediate acquired resistance to FGFR inhibitors in cholangiocarcinoma with FGFR fusions/rearrangements [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2618.