Breast cancer is the commonest cause of cancer related death in women worldwide. Amplification or over-expression of the ERBB2 (HER/neu) gene occurs in approximately 15-30% of breast cancer cases and it is strongly associated with an increased disease recurrence and a poor prognosis. Determination of HER2/neu status is crucial in the treatment plan as that positive cases will respond to trastuzumab therapy. It has been used to test for HER2/neu by immunohistochemistry as a first step and then to study only the equivocal positive cases (score 2+) by in situ hybridization technique. The aim of our study is to compare between immunohistochemistry and silver in situ hybridization (SISH) in assessment of human epidermal growth factor (HER2/neu) receptors status among breast cancer patients. A cross-sectional study was conducted at The Medical City in Baghdad, from October 2016 to April 2017, where formalin fixed, paraffin embedded tumor tissue from 52 female patients (aged 33 to 71 years) with the diagnosis of breast cancer have been included in this study for the evaluation of human epidermal growth factor (HER2/neu) protein overexpression and gene amplification by immunohistochemistry and silver in situ hybridization (SISH) method respectively. Base line data about patients were obtained from their hospital records. The distribution of human epidermal growth factor (HER2/neu) protein overexpression by immunohistochemistry showed that the (+2) score/equivocally positive were seen in 24 cases, which comprise the largest number of cases in this study (46.15%). Ten cases (19.23%) for each of scores 0/negative and +1/negative were present, while (+3) score/positive was the smallest group with only 8 cases (15.38% of cases). All results of SISH were negative in the category of (0 score/negative). In the contrary, all the 8 cases in (+3 score/positive) category were showing positive SISH results. Category (+1 score/negative) HER2 showed two cases (20%) with a positive SISH result, while that of (+2 score/equivocal positive) showed 8 positive cases (about 33.33%). For the detection of HER2/neu protein overexpression and gene amplification, immunohistochemistry (IHC) and in-situ hybridization (ISH) are the recommended techniques, with high concordance between the two techniques, however; performance of silver in situ hybridization in assessment of HER2/neu gene status in all cases of invasive breast carcinoma is recommended as significant number of negative cases by immunohistochemistry showed positive amplification by in situ hybridization and can be treated with anti-HER2 targeted treatments.
