Gefitinib is a medication used primarily to treat certain types of non-small cell lung cancer (NSCLC) that have specific mutations in the EGFR gene. It works by inhibiting the activity of the epidermal growth factor receptor, which is involved in the growth and spread of cancer cells. By blocking this receptor, gefitinib can help slow down or stop the progression of the disease. This drug is typically prescribed for patients whose cancer has not responded to other treatments. It is taken orally, usually in the form of a tablet, and is often part of a targeted therapy approach, which aims to specifically attack cancer cells while minimizing damage to normal cells.