It has been clearly shown that HER2-positive patients, that is, patients whose tumours show strong overexpression of HER2 as indicated by an immunohistochemistry (IHC) score of 3+, and/or whose tumours show HER2 gene amplification as determined by a positive fluorescence in situ hybridisation (FISH) result, derive the greatest therapeutic benefit from treatment with trastuzumab [15,17]. This evidence concerns the gene ERBB2 and neoplasm.