Abstract 405: Using a ctDNA liquid biopsy assay for post-surgical serial monitoring and early detection of disease progression in advanced colorectal cancer patients
Authors: Minarik Marek , Halkova Tereza , Semyakina Anastasiya , Belsanova Barbora , Pudil Jiri , Pazdirek Filip , Levy Miroslav , Simsa Jaromir , Hoch Miroslav , Ryska Miroslav , Benesova Lucie 
Published: August 2019

Abstract
Introduction: ctDNA liquid biopsy has been recognized as a useful approach to monitor effect of ongoing cancer treatment. The ctDNA dynamics is reflecting the overall tumor burden. Here we present a utility of a simple ctDNA assay for longitudinal monitoring of patients with advanced stages of colorectal cancer in conjunction with surgical treatment.
Patients and Methods: In a prospective setting the disease course of a total of 121 patients in Stage III and IV of colorectal cancer was monitored by ctDNA. A panel of somatic mutations was initially screened in primary and/or metastatic tissue. The found mutations were then traced in ctDNA from plasma acquired before surgery and during the subsequent days and months. In a subgroup of rectal cancers ctDNA was also analyzed prior and during the neoadjuvant chemoradiotherapy. The ctDNA levels were then correlated to the clinical parameters such as surgical radicality, disease relapse or response to anticancer therapy.Results: A brief overview of the ctDNA data is shown in Table I.
TABLE I:ctDNA status in patients monitored in this studyTime of plasma samplingctDNA negativectDNA positivesample not availableprior to surgery309102 - 7 days after surgery30 (56%)24 (44%)373 months after surgery18 (54%)15 (46%)216 - 9 months after surgery8 (42%)11 (58%)1412 - 14 months after surgery4 (31%)9 (69%)418 - 24 months after surgery2 (28%)5 (72%)6
A high correlation between the surgical radicality and appearance or absence of ctDNA after surgery was confirmed with 22 of 24 patients with R0 resection as ctDNA negative and 22 of 30 patients with R1/R2 resection as ctDNA positive. Of the 30 ctDNA-negative patients following surgery, 4 patients had ctDNA-detectable progression during the first 9 months and 12 during the next 14 months. At 4 occasions the ctDNA has outperformed CT imaging in detecting the progression. The anti-angiogenic therapy resulted in disappearance or decrease of ctDNA levels in 6 patients during the first month of treatment. In a subgroup of rectal cancers, neoadjuvant chemoradiotherapy resulted in rapid decrease of ctDNA already in the first week of administration. Conclusion: The ctDNA dynamics closely follows clinical course of disease and may serve as a useful biomarker in post-operative follow-up. (supported by AZV 15-27939A)
Citation Format: Marek Minarik, Tereza Halkova, Anastasiya Semyakina, Barbora Belsanova, Jiri Pudil, Filip Pazdirek, Miroslav Levy, Jaromir Simsa, Miroslav Hoch, Miroslav Ryska, Lucie Benesova. Using a ctDNA liquid biopsy assay for post-surgical serial monitoring and early detection of disease progression in advanced colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 405.