HER2 oncogene plays an important role in the oncogenesis and clinical behavior of 25-30% of human breast cancers. Recently, a recombinant humanized monoclonal antibody against HER2 pro- tein, trastuzumab, has been administrated to patients with HER2 positive breast carcinoma. This antibody-based therapy is only effective in HER2-positive carcinoma cases, and therefore, it is very important to evaluate HER2 status with accuracy in order to determine the appropriateness of trastuzumab treatment for the breast cancer patients. Evaluation of HER2 status is mainly performed in the primary breast tumor tissues and several pathological methods, including immunohistochemistry, fluorescence in situ hybridization (FISH) and chromogenic in situ hybridization (CISH) which has been newly developed, are currently used in diagnostic laboratories. In this review, we describe the recent studies about these methods and discuss their reliability and possible further application to various pathological specimens obtained from breast carcinoma patients.
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