Iressa (gefitinib)

Reviewed by: HU Medical Review Board | Last reviewed: July 2022 | Last updated: July 2022

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

It is estimated that approximately 10-20 percent 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 patients who have never smoked (patients may be 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. 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 approximately 30 percent of patients taking gefitinib include diarrhea and skin reactions, such as a rash or acne. Less common side effects experienced in approximately 10-29 percent 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

This is not an exhaustive list of all potential side effects of gefitinib. Talk to your healthcare provider or pharmacist for further information.


Patients receiving gefitinib should talk to their doctor about any other medications (prescription and over-the-counter), herbal remedies, and any supplements they are taking, as well as any other health conditions. If you are pregnant, plan to become pregnant, or are breastfeeding or plan to breastfeed, talk with your doctor. Gefitinib can cause harm to a developing fetus and should not be taken by women who are pregnant. While taking gefitinib, females who can become pregnant should use contraceptives during treatment and for a period of time after completing treatment (patients should discuss appropriate birth control methods, and how long they need to use them, with their doctor). Females should not breastfeed during gefitinib treatment (patients should discuss breastfeeding considerations with their doctor).2

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