Acquired FGFR2 mutation leads resistance to pemigatinib in a patient with FGFR2-driven Borrmann type IV gastric cancer.

Scirrhous gastric cancer (SGC), including the Borrmann type IV subtype, is characterized by a desmoplastic stroma, rapid progression, and a poor prognosis with limited effective treatment options. While fibroblast growth factor receptor 2 (FGFR2) alterations are recognized therapeutic targets in some cancers, their clinical application in gastric cancer, particularly in SGC, remains underexplored. We present the case of a 47-year-old female with advanced, chemotherapy-refractory Borrmann type IV gastric cancer harboring FGFR2 rearrangement and amplification. Treatment with the selective FGFR1-3 inhibitor pemigatinib elicited a marked clinical and serological response; however, disease progression ensued after 3 months. Comprehensive genomic profiling revealed an acquired FGFR2 N549K mutation, a recognized on-target resistance mechanism. Subsequent administration of the irreversible FGFR1-4 inhibitor futibatinib was associated with a declining trend in tumor biomarkers, indicating preliminary antitumor activity against the resistant clone. This case underscores the clinical activity of FGFR inhibition in FGFR2-altered SGC and exemplifies the emergence of kinase domain mutations as a principal resistance pathway. It further suggests that irreversible FGFR inhibitors may represent a rational therapeutic strategy upon progression on prior FGFR-directed therapy, warranting further clinical investigation in this molecularly defined patient subset.