Abstract 770: Exploitation of treatment induced tumor lysis to enhance sensitivity of ctDNA analysis: a first-in-human pilot study
Authors: Breadner Daniel , Vincent Mark David , Correa Rohann , Black Morgan , Warner Andrew , Qu Melody , Logan Diane , Sanatani Michael , Younus Jawaid , Yaremko Brian , Rodrigues George , Blanchette Phillip , Laba Joanna , Yu Edward , Goodale David , Lowes Lori , Bhat Vasudeva , Gratton Albert , Sinfield James , Archer Susan , Morris Clive , Green Emma , Jones Greg , Allan Alison , Palma David , Raphael Jacques 
Published: September 2020

Abstract
Background: Blood based liquid biopsies examining circulating tumour DNA (ctDNA) have increasing applications in non-small cell lung cancer (NSCLC). Limitations in sensitivity, especially in patients with limited disease burden, remains a barrier to ctDNA replacing tissue-based testing. There is a paucity of data regarding the optimal time to measure ctDNA, specifically the dynamics of ctDNA levels in the hours to days following a new and effective treatment. We hypothesize that chemotherapy or radiation will yield an increased abundance of ctDNA in plasma by inducing tumor lysis, allowing for the detection of genetic alterations that were occult in baseline testing.
Methods: Two prospective cohorts of twenty patients (pts) with stage III/IV NSCLC were enrolled. Cohort 1 (C1) contained patients starting the first cycle of platinum doublet chemoradiation (C1a, n=10) or the first cycle of platinum doublet cytotoxic chemotherapy ± immunotherapy without concurrent radiation (C1b, n=10). Cohort 2 (C2) contained patients receiving palliative radiation. Consenting patients provided baseline samples, the first ≤ 14 days prior to starting treatment and one immediately prior to treatment. In C1, subsequent samples were collected (A) 2-3, (B) 4-6, (C) 18-72 and (D) 42-96 hours post initiation of chemotherapy. Pts in C2 had samples collected immediately prior to radiotherapy fractions 2, 3, and 4. Samples were analyzed for ctDNA using the 36-gene amplicon-based NGS Inivata InVisionFirst®-Lung assay.
Results: Complete results were available for the first 28 of 40 enrolled pts, C1a - 8 pts, C1b - 8 pts, C2 - 12 pts. Detectable ctDNA was present at baseline in 21 pts (75%), 4 additional pts (14.3%) had detectable ctDNA in post treatment samples (C1a - 2pts, C1b - 1pt, C2 - 1pt). Three of the patients with detectable ctDNA at baseline (10.7%) had new genetic alterations detected in post treatment samples. A total of 7/28 pts (25%) had new genetic alterations detected in the post treatment samples. Mutant molecule numbers increased with treatment in 19 of 25 (76%) pts with detectable ctDNA, C1 - 11 of 15 pts (73.3%) and C2 - 8 of 10 pts (80%). ctDNA levels peaked a median of 2.2 hours (interquartile range (IQR): 1.5 - 2.9 hours) after the initiation of chemotherapy and a median of 1 day (IQR: 1-2 days) after radiation was commenced. The percentage increase in ctDNA levels was a median of 39.3% (IQR: -20.5 to +112.8%) in C1, with median increases of 22.0% and 39.3% in C1a and C1b, respectively. C2 had a median increase of 81.9% (IQR: 0 to +161.5%).
Conclusion: ctDNA levels increase in the hours to days after starting a new treatment. ctDNA testing in the acute post treatment phase can yield results that were not evident in pretreatment testing. Application of this principle could improve ctDNA utility as an alternate to tissue-based testing and/or improve sensitivity for the detection of treatment-resistant clones.
Citation Format: Daniel Breadner, Mark David Vincent, Rohann Correa, Morgan Black, Andrew Warner, Melody Qu, Diane Logan, Michael Sanatani, Jawaid Younus, Brian Yaremko, George Rodrigues, Phillip Blanchette, Joanna Laba, Edward Yu, David Goodale, Lori Lowes, Vasudeva Bhat, Albert Gratton, James Sinfield, Susan Archer, Clive Morris, Emma Green, Greg Jones, Alison Allan, David Palma, Jacques Raphael. Exploitation of treatment induced tumor lysis to enhance sensitivity of ctDNA analysis: a first-in-human pilot study [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 770.