Dual-color Silver Enhanced in situ Hybridization for Determining HER2

Amplification of the HER2/neu gene in 18-20% of patients with breast cancer produces the primary mechanism of HER2 protein overexpression (PenaultLlorca et al., 2009; Thang et al., 2011; Dekker et al., 2012). The HER2 gene is a tumor marker associated with rapid tumor growth, increased recurrence rate after surgery, and decreased life expectancy (Penault-Llorca et al., 2009; Thang et al., 2011). HER2 positivity has a powerful predictive value related to a good response to anthracycline-based chemotherapy and a poor response to hormonal therapy (Slamon et al., 1987; Paik and Park, 2001). Trastuzumab is a human monoclonal antibody specifically developed against HER2. Sensitive, reliable and the most accurate identification of the HER2 gene is crucial in the selection of patients who will benefit from trastuzumab therapy, since the response to the treatment is directly related to HER2 overexpression. As a result, HER2 amplification in neoadjuvant therapy is directly related to the response to trastuzumab therapy. Baseline HER2/neu status identification with protein and/or genomic status is performed with immunohistochemistry and in situ hybridization (ISH), respectively (Dietel et al., 2007; Carbone et al., 2008; Francis et al., 2009; Bilous et al., 2012). The gold standart for HER2 gene copy number evaluation is considered to be FISH . Dual-color silver in situ hybridization (dc-SISH) technique as an alternative