In vivo studies using a mouse xenograft model implanted with FGFR1-3–altered human tumors all showed antitumor activity of pemigatinib, including models of cholangiocarcinoma expressing the FGFR2-Transformer-2 beta homolog (TRA2b) fusion protein, FGFR2-amplified gastric cancer, FGFROP2-FGFR2 fusion–positive leukemia, and FGFR3-TACC fusion bladder carcinoma.18,19 Taken in combination, the preclinical in vitro and in vivo data show efficacy of pemigatinib across a wide variety of alterations within the FGFR pathway. This evidence concerns the gene FGFR3 and leukemia.