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 tumor tissue. We therefore developed and validated a method of detecting EGFR mutations in these samples. Tumor cells were microdissected 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 exon 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 tumor 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.