Raw research findings for this medication. Mostly single studies, not curated or confirmed robust.
Gefitinib is a targeted cancer medicine, an EGFR tyrosine kinase inhibitor: it blocks the growth signal sent by the EGFR protein on cancer cells. It is used for non-small cell lung cancer whose tumour carries particular EGFR mutations. It is sold as Iressa.
Whether gefitinib works depends above all on EGFR mutations in the tumour itself, such as L858R (rs121434568) and exon 19 deletions; T790M (rs121434569) is linked to resistance. These arise in the cancer and are found by testing tumour tissue, not in the DNA a person was born with. For inherited genes, the US FDA notes that CYP2D6 poor metabolizers have higher gefitinib levels. Studies have also looked at the transporters ABCB1 and ABCG2 and at CYP3A enzymes, with weaker evidence.
Clinical guidelines that name a gene for Gefitinib. They sort people into groups by the gene copies they carry.
US FDA: CYP2D6. CYP2D6 activity score 0.
US FDA: CYP2D6. CYP2D6 activity score 0. Data that Support Therapeutic Management Recommendations.
Every published finding on gene variants and Gefitinib. Upload your DNA file to see which of these rows apply to you.
PharmGKB weighs all studies of a variant and rates how strong the evidence is, from 1A (strongest) to 4.
EGFR rs121434568: Level 1A · replicated. Efficacy: Non-Small Cell Lung Carcinoma. 24.
EGFR rs121434569: Level 2B · replicated. Efficacy: Drug Resistance, Non-Small Cell Lung Carcinoma. 16.
CYP2D6 CYP2D6*1, CYP2D6*2, CYP2D6*5, CYP2D6*10: Level 3. Toxicity: Adenocarcinoma, Drug Toxicity, Exanthema, Non-Small Cell Lung Carcinoma, Toxic liver disease. 5.
EGFR rs11568315: Level 3. Efficacy: Non-Small Cell Lung Carcinoma. 4.
Studies of how quickly the body processes this medication.
Studies of how well it worked in people carrying a variant.
Study findings and evidence levels: PharmGKB (CC BY-SA 4.0). Guidelines: CPIC and DPWG, as bundled in PharmCAT. Most studies were done mainly in people of European ancestry.
More drugs from the same category
Not a prescribing recommendation. This page is educational information about pharmacogenomic research and clinical guidelines - it is not medical or dosing advice, and not a prediction of how any medication will work for you. Never start, stop, or change a medication or dose based on it; talk to your doctor or pharmacist, who can order clinical-grade testing if appropriate.
Content updated September 2026.
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