Plasma ctDNA RAS/RAF mutations analysis for monitoring overall survival (OS) and heterogeneity in metastatic colorectal cancer patients (mCRC).

701Background: The study was designed to estimate the clinical usefulness of genetic analysis for circulating tumor DNA (ctDNA) by digital polymerase chain reaction in patients with mCRC. Methods: We compared B-RAF and K/N/H-RAS mutations detected in surgical or endoscopic ultrasound-guided fine-needle aspiration biopsy tissue DNA and in ctDNA from 63 patients with mCRC. p53 mutational status and PD-L1 expression in the serum and in tissues respectively (positivity H score > 55) were also analyzed with a comparison with survival rates. Results: The frequencies of K-RAS mutations in tissue samples at G12V, G12D, and G12R in codon 12 were 18 of 63 samples (28.57%), 5 of 63 samples (7.93%), and 6 of 63 samples (9.52%), respectively. Conversely, the rates of the mutations in ctDNA were 22 of 63 samples (34.92%), 6 of 63 samples (9.52%), and 9 of 63 samples (14.28%), respectively. No H-RAS or N-RAS mutation were detected. 2 tissue samples harbored a BRAF mutation (3.17%) in a complete discordance with same mut...