Context
ZD1839 or Iressa is a quinazoline tyrosine kinase inhibitor selective for the epidermal growth factor receptor (EGFR). Due to its oral bioavailability and antitumor activity against a broad range of mouse xenograft models, it was selected for clinical development and has now reached phase II-III clinical trials. Although it selectively inhibits EGFR, the molecular bases for the sensitivity to this compound are not fully understood. EGFR overexpression alone does not seem to be neither sufficient nor indispensable for tumor sensitivity to Iressa.