IRESSA, generically known as gefitinib, is a prescription medication used in the treatment of non-small cell lung cancer (NSCLC). It belongs to a class of drugs known as tyrosine kinase inhibitors, specifically targeting the epidermal growth factor receptor (EGFR) pathway, which is often overactive in NSCLC cells. By inhibiting this pathway, IRESSA helps to block the growth and spread of cancer cells. It is particularly effective in patients whose tumors have specific mutations in the EGFR gene. IRESSA is administered orally in tablet form and is typically used as a first-line treatment in suitable patients. As with any cancer therapy, it may cause side effects, and its use is closely monitored by healthcare professionals to manage any adverse reactions and to evaluate its effectiveness in the individual patient's treatment regimen.