EGFR/ErbB2 inhibitor is a cell-permeable inhibitor of EGFR and c-ErbB2 (HER2, Neu; IC50s = 20 and 79 nM, respectively). It inhibits the proliferation of cancer cells overexpressing either c-ErbB2 or EGFR (IC50s = 2.3-2.5 μM). EGFR/ErbB2 inhibitor displays a high level of selectivity for these kinases.