Our aim was to explore the impact of the HER2/neu, HER3 receptor as well as their ligands’ neuregulin (NRG1) expression on the outcome of patients with metastatic colorectal cancer (mCRC). NRG1, HER2/neu and HER3 expression was evaluated in 208 patients with mCRC receiving 5-FU/LV plus irinotecan or irinotecan plus oxaliplatin as the first-line treatment. Biomarker expression was correlated with the outcome of patients. NRG1 (low: 192 vs. high: 16), HER2/neu (low: 201 vs. high: 7) and HER3 (low: 69 vs. high: 139) expressions were assessed in 208 patients. High versus low NRG1 expression significantly affected progression-free survival (PFS) [4.7 vs. 8.2 months, hazard ratio (HR): 2.45; 95% confidence interval (CI): 1.45–4.13; P=0.001], but not overall survival (OS) (15.5 vs. 20.7 months, HR: 1.33; 95% CI: 0.76–2.35; P=0.32). High versus low HER3 expression (PFS: 7.1 vs. 8.8 months, HR: 1.11; 95% CI: 0.82–1.50; P=0.50; OS: 19.8 vs. 21.1 months, HR: 0.95; 95% CI: 0.70–1.30; P=0.75) and high compared with low HER2/neu expression (PFS: 7.7 vs. 8.0 months, HR: 1.07; 95% CI: 0.71–1.60; P=0.75; OS: 16.6 vs. 21.1 months, HR: 1.13; 95% CI: 0.75–1.71; P=0.57) did not influence outcome. High NRG1 expression was associated with inferior PFS in the FIRE-1 trial. We did not detect a prognostic impact of HER2/neu and HER3 overexpression in mCRC. The frequency of overexpression was comparable with other studies.