An orally bioavailable, small-molecule pan-HER tyrosine kinase inhibitor with potential antineoplastic and radiosensitizing activities. Pan-HER kinase inhibitor AC480 binds to and inhibits the human epidermal growth factor receptors (HER) HER1 (EGFR), HER2 (ErbB-2) and HER4, which may prevent downstream signaling and inhibit the proliferation of tumor cells that overexpress these receptors. In addition, this agent may enhance the radiosensitivity of certain tumor cell types that express HER1 and HER2 through cell cycle redistribution in G1 phase and inhibition of DNA repair. EGFRs, frequently overexpressed on tumor cells, play a key role in tumor cell proliferation and survival.