Gefitinib is an EGFR tyrosine kinase inhibitor that binds to the ATP-binding site of the enzyme. It is the first selective inhibitor of the EGFR tyrosine kinase. EGFR is often shown to be overexpressed in certain human carcinoma cells, such as lung and breast cancer cells. Overexpression leads to enhanced activation of the anti-apoptotic Ras signal transduction cascades, subsequently resulting in increased survival of cancer cells and uncontrolled cell proliferation. By inhibiting EGFR tyrosine kinase, the downstream signaling cascades are also inhibited, resulting in inhibited malignant cell proliferation.
It is indicated for the first-line treatment of adult patients with metastatic non-small cell lung cancer (NSCLC), in whom tumors have epidermal growth factor receptor (EGFR) exon 19 deletions or exon 21 (L858R) substitution mutations.