Abstract B24: The significance of postoperative follow-up of patients with advanced colorectal cancer using circulating tumor DNA: Selected case studies
Authors: Benesova Lucie , Belsanova Barbora , Halkova Tereza , Jiri Pudil , Ryska Miroslav , Levy Miroslav , Simsa Jaromir , Pazdirek Filip , Hoch Jiri , Blaha Milan , Minarik Marek 
Published: March 2017

Abstract
Introduction: One of the most notable applications for circulating tumor DNA (ctDNA) detection in peripheral blood of patients with metastatic colorectal cancer (mCRC) is a long-term postoperative follow-up. Sometimes referred to as a “liquid (re)biopsy” it can be performed frequently at relatively short intervals (months or even weeks) with minimal invasivity. The presence of the disease and the actual extent of the tumor burden (tumor mass) within the patient body can be monitored. This is of particular importance especially when evaluating radicality of surgical tratment, monitoring the response to systemic anticancer therapy as well as for early detection of disease progression or recurrence. In this presentation we demonstrate clinical utility of ctDNA detection in a postoperative follow-up setting on several cases of mCRC patients.
Patient cohort: A total of 91 patients undergoing resection of liver metastases were enrolled into the multicentre study involving three surgical centers. In addition to the baseline ctDNA testing a longitudinal observation was conducted for 16 patients by evaluating ctDNA presence (i) prior to surgery, (ii) a week after surgery and (iii) at subsequent intervals over the next several months after the surgery. The presence and the levels of ctDNA were correlated with radicality of surgical treatment and the actual clinical status of the patient. Five separate cases of patients who were followed for over a year by means of ctDNA monitoring are presented.
Results: The R0 (curative) resection correlated with postoperative ctDNA negativity in 4 out of 5 cases of surgical procedures (80%). One of the patients with R0 surgeries, a radio-frequency ablation (RFA) of small liver metastases, continued displaying ctDNA and, subsequently, was diagnosed with the disease recurrence within the scar 3 months after the surgery. A post-surgical ctDNA positivity correlated with one case of R1 (residual tumor) resection. Four patients did show a postoperative relapse of the disease, which was documented in 3 of the cases by increasing levels of ctDNA even as the imaging examination result was negative. In one patient showing remission with no recurrence of tumor the ctDNA remained steadily negative during the entire follow-up period.
Conclusion: CtDNA detection in patients with metastatic CRC is a viable tool for long-term follow-up and early detection of disease recurrence as well as in confirmation of the radicality of surgical treatment. The approach exhibits high specificity and at the minimal invasivity low burden to the patient.
Supported by Ministry of Health of the Czech Republic, grant nr. 15-27939A.
Citation Format: Lucie Benesova, Barbora Belsanova, Tereza Halkova, Pudil Jiri, Miroslav Ryska, Miroslav Levy, Jaromir Simsa, Filip Pazdirek, Jiri Hoch, Milan Blaha, Marek Minarik. The significance of postoperative follow-up of patients with advanced colorectal cancer using circulating tumor DNA: Selected case studies. [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer: From Initiation to Outcomes; 2016 Sep 17-20; Tampa, FL. Philadelphia (PA): AACR; Cancer Res 2017;77(3 Suppl):Abstract nr B24.