Erlotinib: a new therapeutic approach for non-small cell lung cancer

Although treatment with cytotoxic agents has produced modest survival improvement in patients with stage III and IV non-small cell lung cancer (NSCLC), it appears that a plateau has been reached with currently available chemotherapeutic regimens. Increasing knowledge regarding the properties of malignant neoplasms has identified a number of potential therapeutic targets. The epidermal growth factor receptor (EGFR) is one of these targets. Preclinical models have revealed that tumour growth can be inhibited by monoclonal antibodies directed against EGFR and EGFR-specific tyrosine kinase inhibitors. Erlotinib (Tarceva trade mark; OSI Pharmaceuticals, Genentech and Roche), a quinazoline derivative with good oral absorption, is one of several EGFR tyrosine kinases that has been studied in clinical trials. In a Phase I study, mild diarrhoea and mild rash were the most common toxicities. At a dose of 200 mg/day, diarrhoea was the dose-limiting toxicity. The observation that EGFR overexpression is relatively common in NSCLC led to a Phase II trial of erlotinib at the maximum-tolerated dose (150 mg/day) in previously treated NSCLC patients. Erlotinib produced a 12% response rate and there was no apparent relationship between response and tumour EGFR levels. More recent reports suggest that patients who develop a rash have higher responses. Based on its single agent activity, erlotinib has been evaluated in two Phase III trials which compared erlotinib plus chemotherapy to chemotherapy alone in previously untreated NSCLC patients. Erlotinib has also been compared to placebo in a Phase III trial which was limited to advanced stage NSCLC patients whose disease had progressed after two previous chemotherapy regimens. The optimum use of erlotinib in NSCLC will be determined by the results of the completed and future Phase III trials.