Background: We investigated the expression of the EGFR ligands amphiregulin (AREG) and epiregulin (EREG) as well as the amplification of the EGFR-gene in tumor specimens of mCRC patients (pts) treated first-line with anti-EGFR targeted cetuximab together with CAPOX or CAPIRI. Expression levels were correlated with overall response rate (ORR), progression free survival (PFS) and overall survival (OS) to determine their relationship with effectiveness in this setting. Methods: A total of 185 mCRC pts were randomized to cetuximab (400mg/m² day 1, followed by 250mg/m² weekly) plus CAPIRI (irinotecan 200mg/m², day 1; capecitabine 800mg/m² twice daily days 1-14, every 3 weeks; 20% dose reduction of both agents for pts older than 65 years) or plus CAPOX (oxaliplatin 130mg/m² day 1; capecitabine 1000mg/m² twice daily days 1-14, every three weeks). The primary study endpoint was ORR. KRAS mutational status did not correlate with treatment outcome. The cut-offs for EGFR-amplification using FISH, AREG and EREG levels determined by RT-qPCR were calculated using ROC analysis for ORR. Results: Within the subgroup of KRAS wildtype tumors, analysis of EREG- and AREG-expression was possible in 99 pts and of EGFR-amplification in 63 pts. Higher AREG levels correlated significantly with higher ORR (83% vs 46%, p=0.006, OR 0.31), longer PFS (9.6mo vs 4.9, p<0.001, HR 0.35) and longer OS (39.9mo vs 17.2mo, p<0.001, HR 0.36). Higher EREG levels showed a significant correlation with ORR (74% vs 47%, p=0.036, OR 0.54), longer PFS (7.9mo vs 4.9mo, p=0.026, HR 0.57) and OS (33.0mo vs 20.2mo, p=0.041, HR 0.57). EGFR-amplification correlated significantly with higher ORR (71% vs 33%, p=0.004, OR 0.49), longer PFS (8.4mo vs 4.6mo, p=0.004, HR 0.50) and longer OS (30.5mo vs 15.2mo, p=0.001, HR 0.44). Conclusions: In the treatment setting of cetuximab combined with CAIPIRI or CAPOX, AREG, EREG and EGFR-amplification predicted treatment efficacy. Within the subgroup of pts with KRAS wildtype tumors, EGFR-FISH and AREG expression have the strongest relationship with treatment efficacy.