Methodological and TNM Focus-Based Comparison of EGFR Mutation Status in Non-Small-Cell Lung Carcinomas

Epidermal growth factor receptor (EGFR) mutations in non-small-cell lung carcinomas (NSCLC) are a frequent class of driver mutations, and tyrosine kinase inhibitor (TKI) therapy provides considerable clinical benefits. Using the most effective and also easiest method for EGFR analysis is cost-effective and time-saving. In this study, we aimed to determine which method could be more effective by comparing the incidences of EGFR mutations in cytological and histological samples which were obtained by different methods also, whether there was a difference in the incidences of EGFR mutations between the primary foci, mediastinal lymph nodes, and distant metastatic foci. We retrospectively reviewed 420 cases of cytological materials, small biopsies, and surgical samples reported as NSCLC underwent EGFR analysis in our department between 2016 and 2022. We collected the data and interpreted the results from two different perspectives. We identified 36 EGFR mutations in 362 biopsies (9.94%) and 17 in 58 cytology samples (29.31%). There is a significant difference between the two methods (P = 0.01*). We observed 38 EGFR mutations in 320 primary foci (11.87%), 7 EGFR mutations in 36 mediastinal or subcarinal lymph nodes (19.44%), and 8 EGFR mutations in 64 distant metastatic foci (12.50%). A significant difference was also observed in pleural samples (P = 0.005*). We observed more successful results with cell blocks obtained from liquid-based cytological specimens than with formalin-fixed, paraffin-embedded tissues obtained from resection or otherwise in our clinical routine. Our study results highlight the benefits of cytological specimens in molecular treatments and current therapy modalities.