Exploitation of treatment induced tumor lysis to enhance sensitivity of ctDNA analysis: A first-in-human pilot study.

Abstract

3530 Background: Blood based liquid biopsies examining circulating tumour DNA (ctDNA) have increasing applications in non-small cell lung cancer (NSCLC). Limitations in sensitivity remains a barrier to ctDNA replacing tissue-based testing. There is a paucity of data regarding the dynamics of ctDNA levels in the hours to days following a new 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 20 patients (pts) with stage III/IV NSCLC were enrolled. Cohort 1 (C1) contained pts starting the first cycle of platinum doublet chemoradiation (C1a, n=10) or the first cycle of platinum doublet cytotoxic chemotherapy ± immunotherapy without radiation (RT) (C1b, n=10). Cohort 2 (C2) contained pts receiving palliative RT alone. Two baseline samples were collected, the first ≤ 14 days prior to starting treatment and one immediately prior to treatment. In C1, subsequent samples were collected 3, 6, 24 and 48 hours post initiation of chemotherapy. Pts in C2 had samples collected immediately prior to RT 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 35 of 40 enrolled pts, C1a – 10 pts, C1b – 9 pts, C2 – 16 pts. Detectable ctDNA was present at baseline in 27 pts (77%), 4 additional pts (11%) had detectable ctDNA in post treatment samples. Four of the patients with detectable ctDNA at baseline (15%) had new genetic alterations detected in post treatment samples. A total of 8/35 pts (23%) had new genetic alterations detected in the post treatment samples. Mutant molecule numbers increased with treatment in 23 of 31 (74%) pts with detectable ctDNA, C1 - 13 of 19 pts (68%) and C2 - 10 of 16 pts (63%). ctDNA levels peaked a median of 2.2 hours (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 29% (IQR: -18 to +112%) in C1. C2 had a median increase of 16% (IQR: 0 to +131%). Conclusions: ctDNA levels increase in the hours to days after starting 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 improve sensitivity for the detection of treatment-resistant clones.