Research into the role of the human epidermal receptor growth factor receptor 1/epidermal growth factor receptor (HER1/EGFR) in tumorigenesis has generated a new class of anticancer drugs. One such agent, erlotinib (Tarceva), is a potent, selective and reversible inhibitor of HER1/EGFR tyrosine kinase activity. Erlotinib has demonstrated the clinical activity in a variety of solid tumors, and has recently demonstrated improvements in survival in large Phase III trials, in non-small-cell lung cancer and pancreatic cancer.