PD 180970 is an inhibitor of Bcr-Abl. It inhibits wild-type and mutant forms of Bcr-Abl, as well as the p210 isoform, a marker of chronic myelogenous leukemia (CML), with IC values ranging from 5 to 48 nM. PD 180970 is selective for Bcr-Abl over basic FGFR (bFGFR) and PDGFR (ICs = 934 and 1,430 nM, respectively) but also inhibits Src, LCK, KIT, and EGFR (ICs = 0.8, <5, 50, and 390 nM, respectively). It induces cell cycle arrest at the G phase and apoptosis in K562 CML cells when used at a concentration of 50 nM. PD 180970 (500 nM) inhibits constitutive STAT3 DNA-binding activity in, and proliferation of, MDA-MB-468 breast cancer cells. It also inhibits proliferation of Ba/F3 cells expressing mutant p210 Bcr-Abl that are resistant to imatinib with an IC value of 48 nM.