A Sensitive Method for Detecting EGFR Mutations in Non-small Cell Lung Cancer Samples with Few Tumor Cells

Background: Detection of epidermal growth factor receptor (EGFR) mutations in advanced non-small cell lung cancer (NSCLC) patients has relied on DNA purification from biopsies, amplification, and sequencing. However, the number of tumor cells in a sample is often insufficient for EGFR assessment. Methods: We prospectively screened 1380 NSCLC patients for EGFR mutations but found that 268 were not evaluable because of insufficient turner tissue. We therefore developed and validated a method of detecting EGFR mutations in these samples. Turner cells were micro-dissected into polymerase chain reaction buffer and amplified. EGFR mutations were detected by length analysis of fluorescently labeled polymerase chain reaction products and TaqMan assay. Results: We determined EGFR status in 217 (81%) of the 268 primary NSCLC samples not evaluable in our original study-fresh and paraffin-embedded with less than 150 cells. Exon 19 deletions were detected in 11.5% of patients and exon 21 L858R mutations in 5.5%. In addition, the exert 20 T790M mutation was detected in 6 of 15 (40%) patients at the time of progression to erlotinib. The primary, sensitive mutation was present in all turner cells, whereas the T790M mutation was absent in some groups. Conclusions: The method presented here eliminates the need for DNA purification and allows for detection of EGFR mutations in samples containing as few as eight cancer cells.