BACKGROUND: Direct comparisons between Guardant360 (G360) circulating tumor DNA (ctDNA) and FoundationOne (F1) tumor biopsy genomic profiling in metastatic colorectal cancer (mCRC) are limited. We aim to assess the concordance across overlapping genes tested in both F1 and G360 in patients with mCRC. MATERIALS AND METHODS: We retrospectively analyzed 75 patients with mCRC who underwent G360 and F1 testing. We evaluated the concordance among gene mutations tested by both G360 and F1 among three categories of patients: untreated, treated without, and treated with EGFR inhibitors, while considering the clonal and/or subclonal nature of each genomic alteration. RESULTS: There was a high rate of concordance in APC, TP53, KRAS, NRAS, and BRAF mutations in the treatment-naive and non-anti-EGFR-treated cohorts. There was increased discordance in the anti-EGFR treated patients in three drivers of anti-EGFR resistance: KRAS, NRAS, and EGFR somatic mutations. Based on percentage of ctDNA, discordant somatic mutations were mostly subclonal instead of clonal and may have limited clinical significance. Most discordant amplifications noted on G360 showed the magnitude below the top decile, occurred in all three cohorts of patients, and were of unknown clinical significance. Serial ctDNA in anti-EGFR treated patients showed the emergence of multiple new alterations that affected the EGFR pathway: EGFR and RAS mutations and MET, RAS, and BRAF amplifications. CONCLUSION: G360 Next-Generation Sequencing platform may be used as an alternative to F1 to detect targetable somatic alterations in non-anti-EGFR treated mCRC, but larger prospective studies are needed to further validate our findings. IMPLICATIONS FOR PRACTICE: Genomic analysis of tissue biopsy is currently the optimal method for identifying DNA genomic alterations to help physicians target specific genes but has many disadvantages that may be mitigated by a circulating free tumor DNA (ctDNA) assay. This study showed a high concordance rate in certain gene mutations in patients who were treatment naive and treated with non-anti-EGFR therapy prior to ctDNA testing. This suggests that ctDNA genomic analysis may potentially be used as an alternative to tumor biopsy to identify appropriate patients for treatment selection in mCRC, but larger prospective studies are needed to further validate concordance among tissue and ctDNA tumor profiling.