The number of CA tandem repeats (CA)n in a highly polymorphic region of EGFR (epidermal growth factor receptor) intron 1 may affect gene transcription; the potential impact of allelic variants on the efficacy of cetuximab in metastatic colorectal cancer (mCRC) patients is debated for long. This study aimed at prospectively estimating the impact of EGFR intron 1 (CA)n variants on clinical outcome in KRAS exon 2 and BRAF wild-type chemo-refractory mCRC patients, receiving cetuximab and irinotecan. Variants presenting<and ⩾20 CA repeats were defined as short (S) and long (L), respectively. One hundred and fifteen patients were included. No differences in progression-free survival or overall survival were observed between L- and SS genotypes (hazard ratio (HR)=1.00 (95% confidence interval (CI): 0.67-1.50), P=0.991; HR=1.32 (95% CI: 0.81-2.16), P=0.261). Exploratory analyses adopting other cutoff values previously described led to similar results. This prospective study did not confirm any previous retrospective finding, reporting a predictive or prognostic effect of EGFR (CA)n repeats allelic variants in chemo-refractory mCRC patients receiving cetuximab and irinotecan.