J Thorac Oncol. 2012;7: 355–364

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


Hye-Suk Han, MD, Sung-nam Lim, MD, Jin Young An, MD, Ki Man Lee, MD, Kang Hyeon Choe, MD, Ki Hyeong Lee, MD, Seung Taik Kim, MD, Seung-Myoung Son, MD, Song-Yi Choi, MD, Ho-chang Lee, MD, and Ok-Jun Lee, MD

Abstract
Introduction: 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.
Methods: 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.
Results: 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.
Conclusions: 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.

Keywords
Direct sequencing, Epidermal growth factor receptor mutation, Lung adenocarcinoma, PNA clamping, Sensitivity.