Background: KRAS, BRAF, NRAS and exon 20 PIK3CA quadruple wild-type CRC is associated with 41.2% response rate to anti-EGFR treatments. Even in molecular characterized patients, there is still a subset of non responders. The identification of additional predictive biomarkers is an unmet clinical need for treatment personalization. Alterations of ALK oncoprotein may interfere with the biological activity of EGFR through cross-talk of downstream signalling pathways. Methods: This retrospective analysis aimed to investigate the correlation between ALK gene copy number (GCN), assessed by fluorescence in situ hybridization (FISH), and clinical outcome in KRAS/NRAS/BRAF/PI3KCA wild-type chemorefractory advanced CRC patients receiving cetuximab or panitumumab. FISH was perfomed with break-apart ALK (2p23) probes and gain of ALK GCN was defined as a mean of 3 to 5 signals in ≥10% of cells and amplification as ≥6 signals. Association of ALK status with RECIST response was performed by Fisher’s exact test. Results: Forty-one patients were identified, of whom 17 (41%) were ALK GCN positive, whereas the remaining 24 cases (59%) were ALK GCN negative. No ALK translocations were detected. Overall response rate was 19/41 (46%). We observed a partial response in 3/17 patients with ALK GCN positive versus 16/24 patients with ALK GCN negative (18% versus 67%, respectively; P=0.0036). Kaplan-meier curves for comparison of median progression-free and overall survival, as well as correlation with ALK expression by immunohistochemistry, will be presented at the Meeting exploring the whole National Cancer Institute data-set. Conclusions: In this study population with KRAS/NRAS/BRAF/PI3KCA wild-type tumors, the response rate greater than 40% is in line with literature data. ALK GCN may be a biomarker for clinical outcome prediction in advanced chemorefractory CRC patients treated with cetuximab or panitumumab.