Enhanced detection of EGFR mutations in plasma from non-small cell lung cancer (NSCLC) patients using Scorpion primers

Abstract

7682 Background: Activating epidermal growth factor receptor (EGFR) mutations identified in NSCLC patient tumors are often associated with rapid and profound response to EGFR tyrosine kinase inhibitors (TKIs). Conventional detection methods are cumbersome and may underestimate mutations frequencies due to limited sensitivity. We and others have shown that tumor-specific mutations such as KRAS can be detected in tumor DNA shed into patient plasma (Kimura, Ann N Y Acad Sci, 2004). Here we describe the performance of an allele- specific real-time PCR system utilizing Scorpion primers (kindly provided by DxS, UK) to detect EGFR mutations in plasma. Methods: DNA was extracted from archival tumor blocks, slides and plasma obtained from consenting patients. In order to determine the sensitivity of this technique both in terms of the ratio of mutant-to-wild-type genomic DNA as well as the minimum amount of DNA required for detection, a dilution experiment was conducted. Genomic DNA from cell lines containing either the exon 21 L858R point mutation or the exon 21 E746–750 deletion was diluted with wild-type genomic DNA at ratios ranging from 1:2 to 1:10,000. Clinical specimens including plasma and/or tissue from 35 advanced stage NSCLC patients treated with EGFR-TKIs were examined. Results: Mutant DNA was successfully detected when it comprised as little as 0.1% of the total sample or as low as 25 pg of mutant-positive genomic DNA in a pool of 2.5 μg of total DNA. EGFR mutations were identified by this approach in both plasma and tissue of 2 patients who were complete responders to EGFR-TKI therapy, only one of which was detectable by direct sequencing. For the 7 patients where only tissue was available, two were positive both with the Scorpion primers and direct sequencing while the rest were wild-type. Of 21 patients where only plasma was available, 6 mutations were detected using the Scorpion primers. Conclusions: Allele-specific Scorpion technology is 1) highly specific and sensitive for EGFR mutation analysis, 2) able to detect mutations that were not observable by direct sequencing in plasma and tissue, 3) capable of detecting mutations in shed tumor DNA in plasma of advanced NSCLC patients and 4) may be suitable for monitoring response or detecting recurrence. No significant financial relationships to disclose.