Abstract 533: A study of sequencing circulating cell free DNA from lung cancer patients

Abstract Precision oncology requires accurate cancer molecular information. While widely used to characterize tumors, tissue biopsy is limited in patient follow-up due to its invasive nature and the lack representation of the entire tumor bulk. To develop the method of circulating cell free DNA (cfDNA) for obtaining clinically valuable sequence information, we isolated cfDNA from the plasma samples of 10 advanced metastatic lung cancer patients and performed next generation sequencing (NGS) using a unique molecular marker (UMI) integrated 275-gene-target-panel at the average depth of 4,000 X coverage. We were able to identify common mutants of lung cancer driver genes, e.g. EGFR, KRAS, DNMT3 and TP53 with high confidence. In one example, the TKI resistant EGFR mutant T790M was found coexisting with EGFR 746-750del and TP53 splice variant in a baseline sample of a patient progressed from a first-generation EGFR inhibitor. And the dynamic changes of the allele frequency of EGFR and TP53 mutants were consistent with total cfDNA levels of the patients. Interestingly, an osimertinib resistance EGFR mutant C797S emerged at Day 355 post-treatment and followed by disease progression in 4 months. In addition to EGFR gene mutations, we further found increasing EGFR copy number associated with drug resistance and cancer progression of this patient. Our study demonstrated that it is feasible using cfDNA for patient follow-up to understand cancer resistance or disease progression through characterization of cancer mutations. Citation Format: Zhigang Kang, Liang Cao. A study of sequencing circulating cell free DNA from lung cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 533.