ERBB2 and neoplasm: For some patients tested positive with a HER2 IHC or a HER2 in situ hybridization (ISH) assay, treatment with trastuzumab or other HER2 inhibitors does not always result in a positive clinical outcome and in these cases the test result must be regarded as ‘false positive’, which likely is due to involvement of other molecular pathways than HER2 in the tumor progression.