Resistance to Epidermal Growth Factor Receptor-Tyrosine Kinase Inhibitors by Transformation to Small Cell Lung Cancer in an EGFR-mutant Patient

It is important to determine the histological tumor type in non-small cell lung cancer (NSCLC). In patients with adenocarcinoma harboring the epidermal growth factor receptor (EGFR) exon 19 deletion mutation, targeted therapy can yield survival benefit. The epidermal growth factor receptor tyrosine kinase inhibitors gefitinib and erlotinib can provide survival benefit for advanced stage NSCLC patients. However, increasing evidence of acquired resistance to these drugs has been reported, and numerous molecular and biological mechanisms of acquired resistance have been detected. The present report is description of 1, such resistance mechanisms: transformation to small cell lung cancer in a patient who was in the 13th month of erlotinib therapy.