C-erb-2 oncoprotein is the product of the HER-2 (neu) oncogene which is overexpressed in a variety of adenocarcinomas arising at various sites. Overexpression of c-erb-2 is present in 15-30% of cases of breast carcinoma and has been demonstrated to be a negative prognostic indicator. C-erb-2 overexpression can be detected by immunohistochemical staining of formalin-fixed paraffin-embedded sections of tumor tissue. Membrane staining of the cells is the only reaction considered positive. A positive therapeutic response to Herceptin (TM) therapy with anti-C-erb-2 monoclonal antibody has been reported in association with 3+ staining intensity.