Background: Accurate genotyping is mandatory for the management of mCRC pts. Tissue-based testing is still the SoC; however, is not available for all pts. and may be exhausted by serial testing, resulting in incomplete genotyping. We aimed to establish the validity of comprehensive non-invasive ctDNA testing in 1L mCRC pts for whom SoC tissue genotyping was available. Methods: 1L mCRC pts were tested with a comprehensive ctDNA test (Guardant360), a RAS ctDNA test (OncoBeam), and SoC tissue testing at the time of diagnosis. The primary endpoint was NCCN guideline biomarker discovery rate (KRAS, NRAS, and BRAF mutations, ERBB2 amplification, and microsatellite instability). Results: In 91 evaluable pts, the biomarker discovery rate was 54.9% (50/91) for SoC tissue testing, 59.3% (54/91) for comprehensive ctDNA testing (p= 0.0318 for non-inferiority vs. SoC), and 42.9% (39/91) for RAS ctDNA testing (inferiority not rejected vs. SoC). Both comprehensive and RAS ctDNA testing showed high positive agreement (85%, 44/52, and 86%, 31/36) and negative agreement (96%, 268/279, and 93%, 93/100) relative to SoC tissue testing at the gene level. Expanding genotyping beyond KRAS codon 12/13 mutations increased biomarker discovery rate by 56% for tissue testing (50/91 vs. 32/91, McNemar’s p< 0.0001) and by 64% for comprehensive ctDNA (54/91 vs. 33/91, McNemar’s p< 0.0001). Turnaround time was significantly shorter for comprehensive ctDNA testing vs. SoC tissue testing (mean 11.7 days vs. 23.0 days, paired T-test p= 0.0002). On retrospective analysis, 92% of biomarker-positive pts would have been identified at 2 weeks using the comprehensive ctDNA test for initial genotyping with reflex to tissue for biomarker-negative pts, whereas initial use of SoC tissue testing would have identified only 85% of positive pts at 4 weeks (Fisher’s exact p< 0.0001). Conclusions: As previously reported for lung cancer, comprehensive ctDNA testing in 1L mCRC identifies at least as many biomarker-positive pts as SoC tissue genotyping with high concordance to tissue and in half the turnaround time.