Discordance of epidermal growth factor receptor mutations between primary tumors and corresponding mediastinal nodal metastases in patients operated on for stage N2 non-small cell lung cancer.

The discordance of epidermal growth factor receptor (EGFR) mutations between primary lung tumors and the corresponding mediastinal nodal metastases has not yet been well elucidated. We investigate the discordance of EGFR mutations between primary tumors and the corresponding mediastinal nodal metastases, and the discordance of EGFR mutations between different mediastinal lymph node stations in patients operated on for stage N2 non-small cell lung cancer (NSCLC). Two hundred and nineteen surgically resected primary tumors and their 553 corresponding mediastinal nodal metastases were evaluated for EGFR mutations in exon 19 or 21 by TaqMan real-time polymerase chain reaction (PCR) analysis. EGFR mutation was detected in 26.0% (57/219) of the primary tumors and 14.8% (82/553) of the corresponding mediastinal nodal metastases. In 162 cases with EGFR wild-type in primary tumors, none of their 402 corresponding mediastinal nodal metastases had EGFR mutation. In 57 cases with EGFR mutations in primary tumors, EGFR mutations were detected in 82 of all 151 metastatic lymph node stations (54.3%), 34 cases had EGFR mutations in mediastinal nodal metastases, and 23 cases had lost the mutations in mediastinal nodal metastases. Among the 219 cases, 196 cases had at least two metastatic lymph node stations, 9.0% (18/196) of cases with multiple metastatic nodal stations exhibited discordance in EGFR mutations between different lymph node stations. The possibility of discordance in EGFR mutations between primary tumors and corresponding mediastinal nodal metastases, and between different mediastinal lymph node stations should be considered whenever these mutations are used for the selection of patients for EGFR-directed tyrosine kinase inhibitor therapy.