Test Details: Immunohistochemical testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody. The overexpression of HER-2 is noted mainly in breast and gastric adenocarcinomas, in addition to a subset of other carcinoma types such as ovarian carcinoma, non-small cell carcinoma of the lung, salivary gland carcinoma, and urinary bladder transitional cell carcinoma. Over-expression of HER2/neu is associated with poor prognosis of breast, ovarian, bladder, pancreatic, stomach, and oesophageal malignancies. It is a predictive marker for a positive response to a monoclonal antibody, trastuzumab, targeted against the HER2/neu receptor.