Recent evidence indicates that high epidermal growth factor receptor (EGFR) gene copy number evaluated by fluorescence in situ hybridization is an excellent predictive biomarker for response and survival benefit in patients with non-small cell lung cancer who receive epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors. Data on EGFR protein expression by immunohistochemistry as a selection marker are conflicting, although several studies showed that the treatment benefit was confined to EGFR-positive patients. Our studies and others showed that fluorescence in situ hybridization and immunohistochemistry were associated with the best predictive value. Expeditious validation of this information in prospective clinical trials with patient selection to first-line treatment is currently being done or planned by several cancer research groups worldwide.