EGFR Mutation Status in Lung Adenocarcinoma-Associated Malignant Pleural Effusion and Efficacy of EGFR Tyrosine Kinase Inhibitors.

Purpose: Malignant pleural effusions (MPEs) are often observed in lung cancer, particularly adenocarcinoma. The aim of this study was to investigate epidermal growth factor receptor (EGFR) mutation status in lung adenocarcinoma-associated MPEs (LA-MPEs) and its correlation with efficacy of EGFR tyrosine kinase inhibitor (TKI) therapy.

Materials and Methods: Samples comprised 40 cell blocks of pathologically-confirmed LA-MPEs collected before the start of EGFR TKI therapy. EGFR mutation status was re-evaluated by peptide nucleic acid clamping and the clinical outcomes of EGFR TKI‒treated patients were analyzed retrospectively.

Results: EGFR mutations were detected in 72.5% of LA-MPE cell blocks (29/40). The median progression-free survival for patients with EGFR mutations in LA-MPEs was better than that for patients with wild-type EGFR (7.33 months vs. 2.07 months; hazard ratio, 0.486; 95% confidence interval, 0.206 to 1.144; p=0.032). The objective response rate (ORR) of 26 patients with EGFR mutations in LA-MPEs among the 36 patients with measurable lesions was 80.8%, while the ORR of the 10 patients with wild-type EGFR in LA-MPEs was 10% (p < 0.001). Among the 26 patients with EGFR mutations in LA-MPEs, the ORR of target lesions and LA-MPEs were 88.5% and 61.5%, respectively (p=0.026).

Conclusion: EGFR mutation status in cell blocks of LA-MPEs confirmed by pathologic diagnosis is highly predictive of EGFR TKI efficacy. For patients with EGFR mutations in LA-MPEs, the response to EGFR TKIs seems to be worse for pleural effusions than for solid tumors.