Recent trends of HER-2 testing and trastuzumab therapy for breast cancer

Molecular-targeted therapy using trastuzumab, a humanized monoclonal antibody against human epidermal growth factor receptor type-2 (HER-2), is considered to be effective for metastatic as well as primary breast cancer and has already become a worldwide standard therapy for patients with HER-2 protein over-expression and gene amplification. Pretreatment evaluation of HER-2 status is considered to be essential for selection of patients, and according to the generally used algorithm, cases with an immunohistochemistry (IHC) score of 3+ and positivity upon fluorescence in situ hybridization (FISH) are thought to be eligible for trastuzumab therapy. In order to develop an appropriate domestic HER-2 testing system in Japan, the Trastuzumab Pathology Committee was established in 2000 and has been used as a forum for active discussions of policies related to HER-2 testing. After trastuzumab therapy and HER-2 testing had become widely adopted internationally, new guidelines for HER-2 testing were proposed by the ASCO/CAP group in 2007. Since then, these guidelines have gradually become accepted and used in many large-scale clinical studies of HER-2-targeting agents. On the other hand, new ISH methods have been introduced, such as bright-field HER-2 and chromosome 17 centromere double in situ hybridization (BDISH) and dual color-chromogenic in situ hybridization (dc-CISH). These methods make it possible to examine HER-2 gene amplification using only one paraffin section like the dc-FISH method, and to observe grains on the HER-2 gene and centrosome-17 by conventional microscopy. These approaches are considered to be reliable and equally as effective as the dc-FISH method. Accurate evaluation of HER-2 status is thought to be most important for appropriate selection of breast cancer patients who will obtain genuine benefit from trastuzumab treatment. In order to perform effective evaluation of HER-2 status, it is necessary to establish a reliable HER-2 examination system and to maintain its quality at a high level.