Relationship of Thyroid Transcription Factor 1 to EGFR Status in Non-Small-Cell Lung Cancer

Background: Activating mutations of the epidermal growth factor receptor (EGFR) gene are known to drive a proportion of non-small-cell lung cancers. Identification of lung cancers harbouring such mutations can lead to effective treatment using one of the agents that targets and blocks EGFR-mediated signalling. Methods: All specimens received at the BC Cancer Agency (Vancouver) for EGFR testing were prospectively identified and catalogued, together with clinical information and EGFR status, over a 14-month period. Results: Specimens from 586 patients were received for EGFR testing, and EGFR status was reported for 509 patients. No relationship between specimen type or site of origin and EGFR test failure rate was identified. Concurrent immunohistochemical (IHC) status for thyroid transcription factor 1 (TTF1) was available for 309 patients. The negative predictive value of TTF1-negative status by IHC was 94.2% for predicting negative EGFR status. Conclusions: In patients with limited tissue available for testing, a surrogate for EGFR status would aid in timely management. Immunohistochemistry for TTF1 is readily available and correlates highly with EGFR status. In conjunction with genetic assays, TTF1 could be used to optimize an EGFR testing strategy.