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Iressa (gefitinib)

Iressa® is a targeted therapy that is used to treat some non-small cell lung cancers (NSCLC) that have a certain EGFR (epidermal growth factor receptor) mutation, specifically the exon 19 deletions or exon 21 (L858R) substitution mutation. EGFR mutation is determined by biomarker tests (molecular testing) conducted on a biopsy sample of the tumor. Gefitinib is an EGFR inhibitor and is also classified as a tyrosine kinase inhibitor. It is designed to block the activating sites (tyrosine kinases) of several proteins within the cancer cell. These proteins can stimulate cancer growth when the tumor has an EGFR mutation. By blocking the action of the proteins, Iressa may shrink the cancer or slow the cancer’s progression.1,2

Gefitinib is used to treat NSCLC that are positive for EGFR mutation (exon 19 deletions or exon 21 (L858R) substitution) that are metastatic (spread to distant parts of the body) prior to other treatment.2

About EGFR mutations

An estimated 10% of patients with non-small cell lung cancer (NSCLC) in the United States have a tumor mutation associated with EGFR. EGFR mutations are most often found in tumors in female patients who have never smoked (patients are considered “never smokers” if they have smoked less than 100 cigarettes in their lifetime). The tumors are likely to be adenocarcinoma. However, EGFR mutations are not exclusive to this type of NSCLC or non-smokers – mutations have also been found in smokers and in other tumor types.3,4

Receiving gefitinib

Gefitinib is a pill that is taken by mouth once daily. It may be taken with or without food. The dosage of gefitinib is determined by several factors, including the patient’s general health and ongoing response to treatment. Patients should take their medication as prescribed by their doctor. Patients should talk to their doctor if they have any questions, or if they have questions regarding their gefitinib regimen.2

Side effects of gefitinib

Gefitinib may cause side effects, and in some cases, these side effects can be severe. Any side effects should be reported to a health care professional. Side effects experienced in greater than 30% of patients taking gefitinib are diarrhea and skin reactions, such as a rash or acne. Less common side effects experienced in 10-29% of patients receiving gefitinib include nausea, vomiting, itching, poor appetite, and eye irritation. Rarely, severe side effects of pneumonia or inflammation of the lung without infection have occurred, potentially accompanied by difficulty breathing with cough or low-grade fever. Patients experiencing sudden shortness of breath or cough, fever, jaundice (yellowing of the skin or eyes), or severe abdominal pain while taking gefitinib should seek medical care immediately.1,2


Patients receiving gefitinib should talk to their doctor about other medications, herbal remedies, and any supplements they are taking, as well as any other health conditions. Patients should not take aspirin while taking gefitinib without discussing with their doctor. Patients should talk to their doctor before receiving immunizations or vaccinations while taking gefitinib to make sure they are appropriate. Patients who are pregnant or may become pregnant during treatment should discuss their condition with their doctor prior to starting gefitinib, as it may be hazardous to the fetus. Females who can become pregnant should utilize effective birth control (patients should discuss appropriate birth control methods with their doctor) throughout gefitinib treatment and for at least two weeks following the final dose of gefitinib. It is not known whether Iressa passes into breast milk, and patients should not breastfeed while taking gefitinib.2

Written by: Emily Downward | Last reviewed: January 2020.
  1. Iressa product website, AstraZeneca. Accessed online on 9/27/16 at
  2. Chemocare. Accessed online on 9/27/16 at
  3. National Cancer Institute. Accessed online on 8/1/16 at
  4. My Cancer Genome. Accessed online on 8/11/16 at