Site-directed mutagenesis or deletion analysis in theTKD shows that it is involved in EGFR dimerization, auto- and transphosphorylationand also activation of the signaling cascades, all of which have been exploitedin the development of small molecule tyrosine kinase inhibitors (smTKIs) for targeting EGFR in various cancer typesincluding breast cancer. The gene discussed is EGFR; the disease is cancer.