background: human epidermal growth factor receptor-2 (her2/neu) is related to growth factor receptors with alkaline kinase activity and it is regarded as important prognostic and therapeutic factor that can depended on in breast cancer therapy. HER2/neu expression by immunohistochemistry (IHC) is submitted to a great in terob server inconsistency. Subsequently additional confirmatory tests for assessment of gene alterations and amplification status are needed for patients with early or metastatic breast cancer. In situ hybridization techniques and specifically Chromogenic in situ hybridization (CISH) was arise as a practical, cost-effective, and alternative to fluorescent in situ hybridization in testing for gene alterationAims of the study: was to determinate her2/neu gene amplification in (27) breast cancer cases with equivocal her2/neu (2+) detected by IHC by using dual-color chromogenic in situ hybridization (CISH) method and to compare the results with clinic-pathological parameters of those patients like age, stage, grade, ER, PR and ki-67.Methods: twenty seven breast-cancer cases with equivocal HER2-IHC(2+) test results were prospectively collected and reanalyzedusing dual-color CISH (Zyto- Vision) detection kit for further identification of her2/neu gene amplification.Results: Cases with equivocal staining for her2/neu were about 27 cases; these cases were involved in chromogenic in situ hybridization technique to determine the status of her2/neu gene. After CISH study 12(44.4%)cases show her2/neu gene amplification (her2/neu/CEN17 ratio > 2.2).In15 (55.5%) cases out of 27 cases, no amplification of the HER2 gene was shown (her2/neu/CEN17 ratio <1.8).Conclusions: A significant proportion of patients with equivocal IHC(2+) test results show amplification of the HER2 gene by ISH.CISH method has the advantage of diagnosis of gene amplification and revealing tissue histopathology under light microscope.