Potent dual EGFR/ErbB2 tyrosine kinase inhibitor (IC50 values are 0.01 and 0.014 μM respectively). Selectively inhibits growth of human tumor cells overexpressing EGFR and ErbB2 (IC50 values are 0.11 μM for inhibition of HN5, N87 and BT474 tumor cell lines vs. > 30 μM for inhibition of non-tumor cell line HFF). Inhibits tumor growth in vivo by ~ 80% in a murine xenograft model following oral administration.