To characterize the activity of ponatinib in estrogen receptor (ER)-positive breast cancer cells with dysregulated FGFR1, we studied MDA-MB-134 cells in which FGFR1 is amplified. Ponatinib potently inhibited MDA-MD-134 cell growth with a GI50 value of 23 nmol/L (Fig. 5A) and inhibited FGFR1 phosphorylation with an IC50 value of 7 nmol/L (Supplementary Fig. S4A).