Determination of human epidermal growth factor receptor 2 (HER2) amplification using fluorescence in situ hybridization (FISH), chromogenic in situ hybridization (CISH) and automated silver in situ hybridization (SISH)

Human epidermal growth factor receptor 2 (HER2) amplification is an important biomarker in breast carcinoma and its determination has been validated in the past using fluorescence in situ hybridization(FISH). However, HER2 FISH method requires specialized fluorescence microscope, high cost and impermanent signals causing it to be impractical for routine laboratories. The aim of the present study was to determine the expression of HER2 using FISH and another two recent new techniques, such as chromogenic in situ hybridization (CISH) and silver in situ hybridization (SISH). The whole sections of HER2 of 25 primary breast carcinoma cases with borderline positive (2+) immunohistochemistry (IHC) were further validated by using manual dual-color FISH, manual single color CISH and automated single color SISH. A total of 88, 84 and 92% of the cases showed HER2 amplification using FISH, CISH and SISH, respectively. A high level of concordance between FISH and CISH, FISH and SISH, CISH and SISH were observed in 91.6% (p = 0.032, k = 0.619), 96% (p = 0.01, k = 0.779) and 95.8% (p = 0.011, k = 0.778), respectively. SISH technique saved time, CISH equipment was less expensive and their high level of concordance shows that they may be alternatively used in routine laboratories.