Abstract 538: Liquid biopsy approaches for determining pathologic response to neoadjuvant immunotherapy in esophageal cancer
Authors: Canzoniero Jenna VanLiere , Lam Vincent , Belcaid Zineb , Lanis Mara , Rhymee Lamia , Landon Blair , Balan Archana , Marrone Kristen , Forde Patrick , Levy Benjamin , Ettinger David , Schneider Heather , Rodavia Hanika , Battafarano Richard , Yang Stephen , Broderick Stephen , Ha Jinny , Jobe Blair , Zaidi Ali , Thompson Elizabeth , Brahmer Julie , Velculescu Victor , Kelly Ronan , Feliciano Josephine , Anagnostou Valsamo 
Published: July 2021

Abstract
We examined the utility of serial liquid biopsies to monitor clonal dynamics and predict pathologic response in patients with esophageal/gastroesophageal junction (E/GEJ) cancer undergoing treatment with neoadjuvant immunotherapy and concurrent chemoradiation (CA209-906; NCT03044613).
Methods: Using Targeted Error Correction sequencing (TEC-Seq), we performed high-depth next generation sequencing on 79 serial plasma samples from 16 patients with operable stage II/III E/GEJ cancer undergoing treatment with neoadjuvant nivolumab, followed by nivolumab plus chemo-radiation and surgery as part of the CA209-906 trial. Liquid biopsies were evaluated pre-treatment, after each of two cycles of neoadjuvant nivolumab, and after concurrent nivolumab and chemoradiation immediately prior to surgery, for an average of 4 time points per patient. Deep sequencing of matched leukocyte DNA and whole exome sequencing (WES) of pre-treatment tumors was performed. The origin of plasma variants was determined by comparison to tumor WES (tumor-derived) and leukocyte TEC-Seq (clonal hematopoiesis (CH)-derived or germline) and their clonal dynamics over time were evaluated. Resected tumors were reviewed by central pathology and percent residual tumor was estimated. Patients were followed for an average of 2 years post-surgery.
Results: Eight of 16 patients had detectable circulating tumor-derived DNA (ctDNA) at any time point. Additionally, 13 CH-derived mutations were detected in plasma of 8 patients. The number of CH-derived mutations was correlated with increasing patient age. Identification and removal of CH-derived mutations via comparison to matched leukocyte sequencing allowed for accurate assessment of kinetics of bona fide tumor-derived mutations in plasma. Tumor mutation burden as determined by tumor WES was not associated with pathological response (mean baseline mutations per exome 90 vs 81 for patients with residual disease &gt;20% and &lt;20% respectively). Detectable ctDNA at the last pre-surgery time point was found in 3 patients and was associated with residual tumor &gt;20% (50% vs 23% with or without detectable ctDNA respectively). ctDNA clearance, defined as detectable ctDNA at one or more earlier time points that subsequently becomes undetectable before surgery, occurred in 5 patients and was associated with improved pathologic response (80% of patients with ctDNA clearance had residual tumor &lt;=20% and no evidence of disease progression). Furthermore, of the three patients who did not have ctDNA clearance, two subsequently developed disease progression.
Conclusion: Comprehensive analyses of ctDNA from E/GEJ patients undergoing neoadjuvant immunotherapy with concurrent chemoradiation revealed ctDNA dynamics that were associated with pathologic response and disease recurrence. These approaches may be used to identify patients at high risk for disease progression.
Citation Format: Jenna VanLiere Canzoniero, Vincent Lam, Zineb Belcaid, Mara Lanis, Lamia Rhymee, Blair Landon, Archana Balan, Kristen Marrone, Patrick Forde, Benjamin Levy, David Ettinger, Heather Schneider, Hanika Rodavia, Richard Battafarano, Stephen Yang, Stephen Broderick, Jinny Ha, Blair Jobe, Ali Zaidi, Elizabeth Thompson, Julie Brahmer, Victor Velculescu, Ronan Kelly, Josephine Feliciano, Valsamo Anagnostou. Liquid biopsy approaches for determining pathologic response to neoadjuvant immunotherapy in esophageal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 538.