Comprehensive genomic profiling of ctDNA in patients with colon cancer and its fidelity to the genomics of the tumor biopsy.

569Background: The liquid biopsy offers the ability to non-invasively analyze the genome of a tumor through circulating tumor (ct) DNA to identify targetable and prognostic genomic alterations. Few studies have rigorously analyzed ctDNA results and determined the fidelity with which they recapitulate the genomics of the tumor. The clinical utility study (CUS) for FoundationACT (Foundation Medicine, Cambridge, MA; NCT02620527) is a large multi-center prospective clinical study to validate this ctDNA assay for multiple solid tumor types. In this subset of the CUS study, paired specimens from 98 patients with colon cancer were analyzed with comprehensive genomic profiling of the tumor (FoundationOne) and a blood sample (FoundationACT). Methods: Maximum somatic allele fraction (MSAF) was used to estimate the fraction of ctDNA in the sample. The set of genes and targeted regions common to both FoundationOne and FoundationACT were compared for each subject. Results: 60% were male; 73 had stage IV, 17 had stage ...