Targeted therapy of lung cancer refers to using agents specifically designed to selectively target molecular pathways responsible for, or that substantially drive, the malignant phenotype of lung cancer cells, and as a consequence of this (relative) selectivity, cause fewer toxic effects on normal cells. Most previous chemotherapy drugs for cancer were (relatively) nonselective in their activity. Although their exact mechanisms of action were varied and complex, they generally worked by damaging cells undergoing mitosis, which is usually more common in malignant tumors than in most normal tissues. Targeted agents are designed to be selective in their effects by modulating the activity of proteins necessary and essential for oncogenesis and maintenance of cancer, particularly enzymes driving the uncontrolled growth, angiogenesis, invasiveness, and metastasis characteristic of malignant tumors. The increased differential activity usually results in fewer troubling side effects for cancer patients, particularly less nausea, vomiting, and death of cells in the bone marrow and gastrointestinal tract, and increased effectiveness against tumor cells. (en)