Molecular Testing in EBUS-TBNA Specimens of Lung Adenocarcinoma: A Study of Concordance Between Cell Block Method and Liquid-Based Cytology in Appraising Sample Cellularity and EGFR Mutations

Cytological endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) specimens of mediastinal lymph node metastasis are frequently used to perform concomitant diagnosis, staging and genetic testing in non-small-cell lung cancer (NSCLC). The purposes of this single-center retrospective study were to evaluate EBUS-TBNA samples’ adequacy for molecular testing of epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK), and to analyze the concordance between the cell block method and liquid-based cytology (LBC) in appraising the sample cellularity and in detecting EGFR mutation. We retrospectively examined 82 patients who underwent EBUS-TBNA from October 2012 to September 2015 and received a confirmed diagnosis of lymph node metastasis of lung adenocarcinoma. Each sample was processed using both cell block and LBC to carry out DNA analysis (adequacy criterion: tumor cell percentage > 25%) and EGFR mutation testing. Fifty-four patients were male, 66 were current or former-smokers, and the median age was 67 years. The median size of sampled lymph nodes was 14.8 mm. Seventy-one and 66 samples were adequate to perform cell block and LBC, respectively. The κ-statistic (0.78) showed an excellent concordance. EGFR mutation was detected in eight patients using cell block and in seven using LBC, with a simple percentage agreement of 87.5%. ALK translocation was found in two patients. This study demonstrates the feasibility of EGFR mutation analysis with both cell block and LBC, with an excellent concordance between the two methods. Considering that the majority of advanced NSCLCs are diagnosed on cytology specimens, LBC is feasible and needs to be implemented for ancillary tests (immunocytochemistry, molecular analysis).