Abstract CT125: A prospective study of dynamic changes of circulating tumor DNA in surgical lung cancer patients

Objective: Most previous studies about circulating tumor DNA focused on advanced stage cancer patients. We have completed a clinical prospective study (NCT02645318) and showed the feasibility of ctDNA detection in early stage (I-IIA) non-small cell lung cancer (NSCLC) patients, which have been published (Sci. Rep.6,31985,2016). We also investigated its clinical application on early diagnosis and showed our data by oral presentation in American Association of Thoracic Surgery Annual meeting 2016 in Baltimore. Based on our previous study, we further evaluated the clinical value of ctDNA. Few study revealed dynamic changes of circulating tumor DNA in surgical lung cancer patients that no criterion has been established of how to use it for surveillance. The aim of this study is to investigate the elimination rate of circulating tumor DNA level after surgery. This is the first prospective study to evaluate the dynamic changes of ctDNA in surgical lung cancer patients. Method: Consecutive patients with suspected lung cancer who underwent curative-intent lung resection were enrolled prospectively in this study from 11/2016. 10 mL blood samples were taken by intravenous puncture. Plasma samples were obtained before surgery (time A) and at a series of scheduled time-points (2 min to 72 hours, time B to F) after tumor resection. DNA was prepared from 4mL of purified plasma. We designed a multiplex assay based on circulating single-molecule amplification and resequencing technology (cSMART) to simultaneously detect and quantitate hot spot EGFR, KRAS, BRAF, ERBB2, PIK3CA, TP53, ALK, RET and MET plasma DNA variants, with matched white blood cell DNA as controls. Positive plasma mutations were validated in tumor tissue by targeted sequencing. Study protocol (ClinicalTrials.gov identifier NCT02965391) was approved by the Peking University People’s Hospital Medical Ethics Committee (2016PHB156-01). Results: A hundred and seven patients were enrolled, in which 18(16.8%)patients showed detectable driver mutations in the preoperative plasma sample (time A), 9 patients were excluded due to non-radical surgery(3); no plasma of other time-points(2); non-somatic driver mutations (2); no surgery performed(2). Therefore, 9 patients (4 stage I, 3 stage II and 2 stage III) with 11 mutations met the inclusion criteria, which included four EGFR, three TP53, two PIK3CA, one KRAS and one ALK mutations. All of the patients had a decrease of mutation ratio as time went on and dropped to 0 after 72 hours of tumor resection. The average mutation ratio was 2.99%, 1.64%, 0.82%, 0.03%, 0.015% and 0 at the time-points A to F, respectively. The evaluated half-life of ctDNA was about 10 min. The total DNA template appeared higher post-operation than pre-operation (3082±2234 vs.1787±1181, p=0.12).One patient had concurrent driver mutations of PIK3CA E545K and EGFR L858R. PIK3CA was detected in time A and decreased gradually from time B to C. EGFR was not detected in time A but in plasma time B and decreased in time C. Conclusion: The elimination of ctDNA in lung cancer patients is very rapid after surgical resection. The intraoperative manipulation may not only push forward releasing of cell free DNA, but also lead heterogeneous tumor mutation discharging to plasma. Detection of ctDNA 72h after surgery could be the reference value for postoperative surveillance. Note: This abstract was not presented at the meeting. Citation Format: Kezhong Chen, Fan Yang, Heng Zhao, Tianyang Wang, Lien Tu Wang, Jun Wang. A prospective study of dynamic changes of circulating tumor DNA in surgical lung cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT125. doi:10.1158/1538-7445.AM2017-CT125