Iressa is an anticancer drug that inhibits an enzyme (tyrosine kinase) present in lung cancer cells, as well as other cancers and normal tissues, that appears to be important to the growth of cancer cells. Iressa is used as a single agent for the treatment of non-small cell lung cancer (NSCLC) that has progressed after, or failed to respond to two other types of chemotherapy (drugs used to kill cancer cells). and is being studied in the treatment of other types of cancer. It belongs to the family of drugs called epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors. Also called ZD 1839.