Application of PCR methods to evaluate EGFR, KRAS and BRAF mutations in a small number of tumor cells in cytological material from lung cancer patients

The epidermal growth factor receptor (EGFR) mutation status in the tyrosine kinase domain is known to be a predictor of the response to gefitinib or erlotinib in lung cancer; thus, a non-surgical procedure of tumor specimen collection is critical for mutation analysis. The aim of the present study was to analyze the EGFR, KRAS and BRAF status in limited cytological material. To the best of our knowledge, this is the first time that the quantitative scale of tumor cells and the percentage of tumor cells in cytological material were evaluated at the early stages of pathomorphological material qualification for EGFR, KRAS and BRAF mutation analysis. Our results revealed that even 100-1,000 tumor cells from fine needle aspiration (FNA) samples provided reliable results of mutation analysis when sensitive real-time polymerase chain reaction (PCR) methods were used. EGFR mutations were detected in 10% (7/71) and KRAS mutations were detected in 35% (19/54) of the lung adenocarcinoma cases. In addition, we reported the most common inhibiting mutation (p.T790M) found in coexistence with p.L858R in an FNA sample from a patient, for whom short-term improvement after erlotinib treatment was observed before further progression of the disease. Subsequently, mutual exclusion of EGFR and KRAS mutations was observed. Cytological samples with a small number of tumor cells obtained via FNA, endobronchial ultrasound (EBUS)-transbronchial needle aspiration (TBNA) or brushing are suggested to be used for diagnostic purposes after careful selection by cytopathologists and analysis using a validated, sensitive real-time PCR method.