EGFR-IN-42 (Compound 17b) is a potent inhibitor of EGFR with single-digit nanomolar activity. EGFR-IN-42 connects tamoxifen or endoxifen with the EGFR-inhibitor gefitinib via a covalent linkage. EGFR-IN-42 retains both ER antagonist activity and EGFR inhibition. EGFR-IN-42 has superior anti-cancer activity.