A drug used to treat certain types of non-small cell lung cancer. It is also used with gemcitabine hydrochloride to treat pancreatic cancer that cannot be removed by surgery or has spread to other parts of the body. It is being studied in the treatment of other types of cancer. Erlotinib hydrochloride blocks a protein called epidermal growth factor receptor (EGFR), which may help keep cancer cells from growing. It is a type of EGFR tyrosine kinase inhibitor. Also called CP-358,774, OSI-774, and Tarceva.