Targeted FGFR Blockade for the Treatment of Tumor-Induced Osteomalacia

This correspondence reports the successful use of the FGFR13 tyrosine kinase inhibitor infigratinib in a 66 year old male with metastatic phosphaturic mesenchymal tumor harboring an FN1 FGFR1 fusion gene. The patient, who had persistent disease despite multiple surgeries, demonstrated rapid biochemical and radiographic responses to infigratinib, including normalization of FGF23 levels (from 15,500 to 180 RU/mL), improved phosphate levels, and tumor regression on PET-CT. Metaplastic transformation of sarcomatous lesions to lamellar bone was observed. Though treatment was intermittently discontinued due to side effects, reinitiation produced similar responses. The case highlights FGFR1 as a therapeutic target in unresectable tumor induced osteomalacia and demonstrates the potential of precision medicine in managing this rare condition.

This correspondence reports the successful use of the FGFR13 tyrosine kinase inhibitor infigratinib in a 66 year old male with metastatic phosphaturic mesenchymal tumor harboring an FN1 FGFR1 fusion gene. The patient, who had persistent disease despite multiple surgeries, demonstrated rapid biochemical and radiographic responses to infigratinib, including normalization of FGF23 levels (from 15,500 to 180 RU/mL), improved phosphate levels, and tumor regression on PET-CT. Metaplastic transformation of sarcomatous lesions to lamellar bone was observed. Though treatment was intermittently discontinued due to side effects, reinitiation produced similar responses. The case highlights FGFR1 as a therapeutic target in unresectable tumor induced osteomalacia and demonstrates the potential of precision medicine in managing this rare condition.