TKI258 treatment results in a dose-dependent reduction in cell survival in 4 EMS patients but not in 2 MPD patients without FGFR1 rearrangements. Cell counts (mean ± SE) are plotted relative to untreated control (dotted line at 1.0) at each time point for 20 nM (▴) and 100 nM (▾) TKI258-treated cell cultures.