e14520 Background: In the era of precision medicine, liquid biopsy analysis is well accepted based on advantages including availability, non-invasiveness, and non-heterogeneity. However, the circulating tumor DNA (ctDNA) in liquid biopsy is diluted by a large excess of wild-type alleles, which necessitates high sensitivity approach for ctDNA detection. In addition, ctDNA analysis from different liquid biopsy samples need to be evaluated. Methods: We have developed a novel mutant-capture based method, termed PErsonalized Analysis of Cancer (PEAC), for high sensitivity detection of cancer driver mutants at abundance as low as 0.01-0.1% for circulating free DNA (cfDNA) standards. ctDNA samples were extracted from body fluids of lung cancer patients including plasma, pleural effusion and cerebrospinal fluid. EGFR mutants predictive of EGFR tyrosine kinase activity were enriched using PEAC technology, and analyzed using Sanger sequencing. Results: Plasma ctDNA samples B7110003, B7110010, and B7112012 had no or barely detectable L858R mutation, which was enriched to 50-90% after PEAC and readily detected by Sanger. T790M was undetectable before PEAC in plasma sample B7112052 and became 50% after PEAC enrichment. Pleural effusion samples E8106029 and E8111305 had dominated L858R and T790M peaks, respectively, in Sanger chromatograms after PEAC, which was almost to the background levels prior to PEAC. Interestingly, both EGFR L858R and T790M mutants were detected in pleural effusion sample E8106029 after PEAC; the sample was from a patient who had previously treated with an EGFR tyrosine kinase inhibitor (TKI), suggestive of resistance developed after target therapy and the utility of PEAC in monitoring patient’s response to EGFR TKI. In addition to enriching point mutations, we also established enrichment of the most frequently occurred EGFR 19 deletion, E746_A750del (c. 2235_2249 del15), which were dominant after PEAC enrichment of ctDNA from plasma samples (B8101186 and B8101241), pleural effusion (E8108088) and cerebrospinal fluid (C8108095); the mutants were undetectable without PEAC enrichment. Conclusions: PEAC technology can enrich ctDNA from body fluids in lung cancer patients and allow detection of low abundant mutants predictive for EGFR TKI therapy. With further validation, the technology may improve current detection methods used in clinical practice.
P34.05 Perioperative Driver Mutation Detection in Circulating Tumor DNA from Lung Cancer Patients across Multiple Timepoints