KU004, a potent dual EGFR/HER2 inhibitor, exhibits anticancer properties. It inhibits the proliferation of human breast cancer SKBR3 cells by inducing G1 phase arrest. KU004 blocks the activation of HER2, EGFR, and the downstream Akt and Erk pathways, primarily inducing apoptosis (Apoptosis) through the extrinsic pathway. Additionally, KU004 is a novel quinazoline derivative.