KU004 is a potent dual EGFR/HER2 inhibitor with anticancer effects. KU004 inhibits the proliferation of human breast cancer SKBR3 cells by inducing G1 phase arrest. KU004 blocks the activation of HER2 , EGFR and downstream Akt and Erk pathways and induces cell Apoptosis mainly via the extrinsic pathway. KU004 is a quinazoline derivative.