572 Background: MET inhibition is emerging as a potent therapeutic strategy and MET gene amplification has shown predictive significance. MET amplification rate in mCRC, as previously reported in literature, varies from 9% in primary to 18% in metastases but intermixes increased copy number from chromosomal level aberrations with focal gene amplification. Validation of MET amplification rate in mCRC is needed. Methods: We performed analyses of MET amplification in mCRC patients (pts) (n = 636) across multiple cohorts. Cohort 1 (n = 103) included tissue microarray from liver metastases analysed using fluorescence in situ hybridization (FISH) [cMET and CEP7 probes, MET/CEP7 ratio > 2]. Cohort 2 (n = 205) included pts referred for phase I trials who had MET amplification testing using FISH. Cohort 3 (n = 279) included cases sequenced with HiSeq (Illumina) with full exome coverage for 202 genes including MET (average depth 800) with focal gene amplification (≥ 4 copies) identified by an in-house algorithm. Cohort 4 (n = 49) included pts refractory to EGFR monoclonal antibodies enrolled in the ATTACC (a prospective molecular screening) program for mCRC, in whom plasma circulating-free DNA (cfDNA) was analyzed by Guardant sequencing technology. Results: In tissue based analyses, focal MET amplification rate was 1.7% and was higher in primary tumors compared to metastases [3.1% (9/291) vs. 0.4% (1/288), p = 0.02] [Table]. In cohorts 2 & 3 MET amplification was found in 4 [MET/CEP7: 2.1 – 7.7; primary (4/130), metastases (0/75)] and 6 [copy number: 4.0 – 6.7; primary (5/161), metastases (1/110)] cases, respectively. MET amplification rate in pts who had progressed on anti-EGFR therapy was 14.3% (Table). Conclusions: Contrary to prior reports, in this large cohort, MET amplification was a rare event in mCRC pts and the rate was not higher in metastatic sites. However, MET amplification occurred in a sizable subset of pts refractory to anti-EGFR therapy as identified by cfDNA analysis. MET amplification appears to play a minor role in de novo colorectal carcinogenesis but may play an important role in acquired resistance to anti-EGFR therapy. [Table: see text]