Overexpression or HER-2 gene amplification occurs in approximately 25% of invasive breast cancers and predicts response to the targeting therapeutic antibody trastuzumab (1). In this report, trastuzumab was used in the treatment of a patient with metastatic colorectal cancer harboring HER-2 gene amplification and overexpression. There was a marked radiographic response to the trastuzumab. If a larger series confirms the efficacy of trastuzumab use in patients with colorectal cancers with HER-2 gene amplification, trastuzumab could help improve the outlook for patients with this unusual colorectal cancer variant.