Predictors Of Clonal Evolution In Metastatic Colorectal Cancer Patients

3604 Background: Concordance of somatic mutations between primary and metastatic colorectal tumors is high in colorectal cancer (CRC), circulating cell-free DNA (cfDNA) accurately reflects the mutation status of metastatic disease. Intervening treatment and metastatic dissemination may result in clonal evolution from pre-existing intratumoral heterogeneity, with the resulting discordance in minor clones.Methods: Patients (pts) were prospectively consented for collection of cfDNA from plasma samples for sequencing on a 54-gene platform optimized for very low allele frequencies (Guardant360), with concurrent sequencing of clinically available and macrodissected historic FFPE tissue (50-gene Ion-Torrent panel), both performed in CLIA-compliant labs. Eligible cases had plasma and tissue sequencing where the modal mutation was present with ≥ 1% and ≥ 5% allele frequencies, respectively. Minor clones were defined as those with an allele frequency u003c 10% of the highest detected allele frequency in the sample.Resu...