A drug used to treat certain types of non-small cell lung cancer. It is also used together with gemcitabine to treat pancreatic cancer and is being studied in the treatment of other types of cancer. Erlotinib is a type of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor. Also called CP-358,774, erlotinib hydrochloride, OSI-774, and Tarceva.