Association of co-occuring mutations in exosomal DNA and clinical outcomes of patients with metastatic colorectal cancer.

Abstract

e15001 Background: Blood-based liquid biopsies offer easy access to genomic material for molecular diagnostics in cancer. Compared with cell-free DNA (cfDNA) derived from apoptotic cells, exosomal nucleic acids (exoNAs) released from living cells, which include more complete DNA, RNA and protein component, can better reflect underlying cancer biology. However, little evidence supports the clinical relevance of such a biomarker in metastatic colorectal cancer (mCRC). Methods: From May 2013 to July 2016, patients with mCRC received chemotherapy with or without molecular targeted drugs were enrolled in the Fifth Medical Center, General Hospital of PLA. Clinical response was evaluated using RECIST 1.1. Serial blood samples were collected and used to extract exosomal DNA. Targeted amplicon ultradeep sequencing was employed to analyze mutations in exosomal DNA with a customized-designed 10-genes panel including prognostic-related and cetuximab-resistant genes of CRC. Results: 91 patients were enrolled in this study, and median follow-up time was 11.7 months. In total of 82 pretreatment samples, 58% were detected to harboring mutations in designed targeted regions. The most frequent mutant genes were TP53 (56%), KRAS (54%), and PIK3CA (33%). Co-occuring genes were detected in 25 (31%) patients, including 16 patients with mutation in both KRAS and TP53 gene. Patients with co-occurring TP53/KRAS mutations showed significantly poor outcome (median OS=9.23m ), than those without co-occuring in these two genes (median OS=18.75m; P=.0141). Further analysis showed progress disease with new metastasis was enriched in patients with co-occurring KRAS/TP53-mutant patients (p=.0016). Of 23 samples from progressed patients received cetuximab, 39% were detected with acquired cetuximab-resistance related mutations in KRAS (26%), PIK3CA (17%), NRAS (4%) and BRAF (4%). In addition, exosomal DNA abundance increased was observed at or before disease progression (mean leading time = 8.90 weeks). Conclusions: This study provided clinical evidence for exosomal DNA as a potential biomarker of prognosis and cetuximab-resistant mechanism of mCRC.