Application of FISH Technique in Evaluation of Equivocal Cases of HER2/neu in Breast Carcinoma

Background: Breast cancer in Iraqi females is one of the extreme popular malignant tumors. It represents the third of registered female cancers. Management and outcome of breast cancer are affected by variables such as tumor size and grade, as well as histologic type, HER2/neu status of the tumor and hormone receptor status. HER2/neu (or erbB-2) is a proto-oncogene found on chromosome 17, that is overexpressed and/or amplified in 15% to 25% of invasive breast carcinomas and is connected to worse clinical outcome. Patients with HER2/neu positive breast carcinoma have showed a good response to targeted therapy (Herceptin) that improving the prognosis. Objectives: To assess the immunohistochemical overexpression of HER2/neu in breast carcinoma, to detect the frequency of amplified HER2/neu by FISH on immunohistochemically equivocal cases, and to correlate HER2 overexpression & or amplification with various clinicopathological parameters. Patients and Method: A total of hundred breast carcinoma patients at different ages were included in this retrospective and prospective case series study design. Formalin fixed paraffin embedded blocks were collected from different private labs in Mosul, between 1st November 2019 to 1st April 2020. FISH technique was performed on 25 equivocal cases of HER2/neu tested by immunohistochemistry technique using Leica Kreatech TM FISH Dual Probe (Red/Green). Results: Among a total of 100 patients with mean age was (52) years old diagnosed as breast carcinoma via histopathological findings, 58% were tested negative for HER2/neu,17% positives for HER2/neu, and 25% were equivocal by Immunohistochemistry. However, FISH method is conducted for those patients indicated as equivocal at immunohistochemistry and has identified 7(28%) positive cases and 18(72%) negative cases. The association between HER2/neu and the grade of the tumor was statistically considerable (P value=0.03). Furthermore, the analysis indicated that the HER2/neu was not statistically related with histological type of the tumor and age of the patients (P value=0.35, P value= 0.75, respectively). In this study, HER2/neu was statistically inversely associated with both ER and PR receptors (P value=0.03, P value=0.05, respectively). Conclusion: HER2/neu is overexpressed by immunohistochemistry in 17%. HER2/neu is amplified by FISH (in equivocal cases) in 28%. HER2/neu is statistically significant correlation with tumor grade, and is in inverse statistically significant correlation with estrogen and progesterone receptors while not statistically significant with age and histological types of tumors.