A selective inhibitor of the fibroblast growth factor receptor tyrosine kinase (IC50s = 0.2, 2.5, and 1.8 nM for FGFR1, 2, and 3, respectively); demonstrates antiproliferative activity in tumor cell lines expressing deregulated FGFRs (IC50s = 18-281 nM) and in an FGFR-driven human tumor xenograft model (12.5 mg/kg/day).