AG 556 is primarily used as a selective inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase. It is widely applied in biochemical and pharmacological research to study signal transduction pathways involved in cell proliferation, survival, and differentiation. Due to its ability to block EGFR-mediated signaling, AG 556 is used in cancer research, particularly in studies targeting tumor growth and metastasis in epithelial cancers. It also serves as a tool compound for validating the role of EGFR in various cellular models and for screening potential therapeutic agents. Its specificity makes it valuable in experiments requiring precise modulation of kinase activity without broad-spectrum interference.