HER2 gene amplification or overexpression of the HER3/4 ligand, heregulin, was significantly associated with lower RR and shorter PFS and OS after treatment with cetuximab (with or without chemotherapy).HER2 gene amplification was specifically related with non-response to cetuximab in CRC patient-derived tumor xenografts. The gene discussed is ERBB3; the disease is neoplasm.