Detection of EGFR Mutation Status in Lung Adenocarcinoma Specimens with Different Proportions of Tumor Cells Using Two Methods of Differential Sensitivity

To evaluate epidermal growth factor receptor (EGFR) mutation status in lung adenocarcinoma specimens with different proportions of tumor cells using two methods with different sensitivities. EGFR mutation status was determined by peptide nucleic acid (PNA) clamping and direct sequencing. The samples consisted of 41 cell blocks of malignant pleural effusions with various proportions of tumor cells, as well as 23 lung biopsy specimens containing more than 20% tumor cells and the corresponding surgically resected tumors. In the analysis of malignant pleural effusions, EGFR mutations were detected only by PNA clamping in four of nine patients who exhibited partial response to EGFR tyrosine kinase inhibitors; all the cell blocks of these four patients contained less than 20% tumor cells. Direct sequencing revealed wild-type EGFR, whereas PNA clamping revealed mutant EGFR, in one of five patients who exhibited progressive disease in response to EGFR tyrosine kinase inhibitor; the cell block of this patient contained a high proportion of tumor cells. A comparison of biopsy specimens containing sufficient tumor cells and the corresponding surgically resected tumors revealed discordance in the EGFR mutation status in four patients based on PNA clamping, whereas no discrepancies were observed by direct sequencing. Highly sensitive methods, such as PNA clamping, may be superior to direct sequencing for the detection of EGFR mutations in diagnostic specimens with a low proportion of tumor cells. Direct sequencing may be more representative when diagnostic specimens with a high proportion of tumor cells are available.