Abstract B021: Saturation mutational scanning uncovers druggability of all FGFR kinase point mutations

Abstract Variants of unknown significance represent one of the biggest challenges for genomics-based precision oncology. High throughput functional genomics is thus essential to characterize the vast number of cancer mutations and tailor the most promising treatment accordingly. Aberrantly activated fibroblast growth factor receptors (FGFRs) frequently drive tumorigenesis with a variety of genetic aberrations across a wide range of tumor entities. Approved selective inhibitors (FGFRis) are available. However, it remains largely unknown which of the many different point mutations affecting FGFR1, FGFR2, FGFR3 or FGFR4 are druggable, i.e. activating FGFR signaling while not mediating FGFRi resistance thereby substantially limiting the therapeutic potential of approved FGFRis. Here, we implemented a saturation mutational scanning platform to screen all 11520 possible point mutations covering the kinase domains of FGFR1-4. In pooled positive selection screens, we identified 474 activating mutations and 738 resistance-mediating mutations to the FGFR inhibitors pemigatinib and/or futibatinib - with many clustered in particular structural elements. Combining these comprehensive datasets revealed 301 druggable FGFR point mutations analogous to a strong PS3/BS3 evidence level. Notably, mutations in the same codon or the corresponding mutations in different FGFRs could strongly differ in their impact, thus underlining the necessity for a saturation approach to study each mutation individually. The screens also identified loss-of-function mutations and FGFR2-specific activating nonsense mutations. Importantly, the functional screens identified 97% of acquired resistance mutations in a clinical trial. In summary, we provide a comprehensive and clinically highly relevant catalog of every single druggable point mutations in the FGFR kinase domains which is readily available for clinical decision support to select the optimal cancer therapy and to push the boundaries of approved inhibitor applications. Citation Format: Carla Tangermann, Avantika Ghosh, Martin Ziegler, Francesco Facchinetti, Jannis Stappenbeck, Marisa Riester, Luise Carmina Viardot, Tobias Zundel, Luc Friboulet, Antoine Hollebecque, José Naveja Romero, Angela Wanninger, Maria Elena Hess, Tilman Brummer, Melanie Börries, Sonja Loges, Yohann Loriot, Lena Illert, Sven Diedrichs. Saturation mutational scanning uncovers druggability of all FGFR kinase point mutations [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Functional and Genomic Precision Medicine in Cancer: Different Perspectives, Common Goals; 2025 Mar 11-13; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(5 Suppl):Abstract nr B021.