Difference in appearance of KRAS mutated circulating tumor DNA in patients with metastatic colorectal cancer during treatments.

Abstract

e23025 Background: Emergence of KRAS mutation in blood is observed in colorectal cancer patients who undergo chemotherapy, but its clinical significance is not well known. In this study, we focused on the difference in appearance of KRAS mutated circulating tumor DNA (MctDNA) and elucidated its association with treatments. Methods: Four hundred and fifty-one plasma samples were collected prospectively from 85 patients (pts) who underwent chemotherapy due to metastatic colorectal cancer in 2014 - 2016. Seven types of KRAS mutation in MctDNA were detected by droplet digital PCR creating oil droplets. To exclude false positive detection, mutation was validated. MctDNA amplified in oil droplets was selectively sorted by On-chip sorting system and mutation was determined by Sanger sequencing. Results: KRAS assessment in tumor tissues showed 29 pts with KRAS mutation (MT), 56 pts without KRAS mutation (WT). Among 29 pts with MT, KRAS assessment in plasma displayed 23 pts with MctDNA and 6 pts without MctDNA. The type of mutation in MctDNA was consistent with that detected in tumor tissues, indicating mutual exclusivity in KRAS mutation was confirmed. In 56 pts with WT, 28 pts showed MctDNA during treatments. Difference in appearance of MctDNA was recognized in several treatments. Gradual increase in detection of MctDNA was observed with anti-EGFR antibody, resulted in treatment resistance. Transient spike elevation was frequently seen in TAS-102, which associated with drug response. No specific appearance was recognized during treatments with other drugs including anti-VEGF antibody. MctDNA in oil droplets were successfully sorted even if a few droplets were targeted, and mutation was confirmed. Conclusions: Difference in appearance of MctDNA may associate with treatment response in patients with metastatic colorectal cancer during treatments. [Table: see text]