Abstract 1338: The application of circulating tumor DNA analysis for detecting minimal residual disease and predicting recurrence in colorectal cancer patients
Authors: Chan Hiu Ting , Nagayama Satoshi , Chin Yoon Ming , Hayashi Rie , Kiyotani Kazuma , Nakamura Yusuke , Low Siew-Kee 
Published: August 2019

Abstract
Background: Although the prognosis of colorectal cancer (CRC) has improved in the past decade, a subset of CRC patients may still suffer from relapse due to the progression from minimal residual disease (MRD) after surgical resection. A sensitive and non-invasive method to efficiently detect MRD is critically essential to further improve the cure rate. In this study, we have evaluated the feasibility of circulating tumor DNA (ctDNA) analysis in detecting MRD in CRC patients. Methods: Plasma samples were prospectively collected from 45 CRC patients, ranged from stage I to IV, who underwent surgical resection. A preoperative blood sample was taken just before surgery and post-operative samples were collected on multiple time-points to monitor the changes of mutation profiles. Cell-free DNA/RNA (cfDNA/RNA) were extracted for library construction using Oncomine Pan-Cancer Cell-Free Assay and were subjected to next-generation sequencing. Results: Sufficient amount of cfDNA/RNA was extracted from 39 of the 45 pre-operatively samples for sequencing. The median input was 19 ng (ranged from 8-20 ng). The median of molecular coverage and barcode tagging efficiency of the sequencing were 4,344x and 83%, respectively. Twenty-seven (69%) of 39 pre-operative patients were found to have at least 2 copies of somatic mutations. Seven samples (ranged from stage I to IV) showed an increase in mutant allele frequency (MAF) postoperatively. The median increase in MAF ranged from 1.2-fold to 7.9-fold with a median of 2.0-fold. One of the 7 patients showed an increase in MAF relapsed 6 months after the primary tumor resection. This stage IIIb patient carried BRAF-V600E with a MAF of 0.067% pre-operatively, showed an 8-fold increase (0.530%) in MAF at the time of diagnosis of recurrence, and showed further increase in MAF to 0.685% at the time of surgical removal of the metastatic lesions. The MAF of BRAF-V600E was reduced to 0.1759% one month after the surgery. The dynamic changes in the MAF detected in ctDNA appears to reflect the recurrence status which might not be detected by imaging tests or currently available biomarkers such as CEA (&lt; 5ng/mL before and after tumor resection in this case). Conclusions: Our current results indicate that ctDNA analysis before and after resection allows the detection of MRD in CRC patients. The integration of ctDNA analysis with current standard monitoring guidelines holds great promise in the early detection of recurrence to allow clinical intervention to be applied promptly.
Citation Format: Hiu Ting Chan, Satoshi Nagayama, Yoon Ming Chin, Rie Hayashi, Kazuma Kiyotani, Yusuke Nakamura, Siew-Kee Low. The application of circulating tumor DNA analysis for detecting minimal residual disease and predicting recurrence in 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 1338.