The Comparison of Automated Silver in situ Hybridization and Fluorescence in situ Hybridization for Evaluating HER2 Gene Amplification in Breast Carcinoma

Purpose: We want to validate the use of the silver-enhanced in situ hybridization (SISH) technique as comparised with fluorescence in situ hybridization (FISH) technique for assessing the HER2 gene amplification of breast carcinoma. Methods: Tissue microarray (TMA) blocks from 58 breast cancer specimens were prepared and the concordance between HER2 gene amplification in breast cancer was determined by the FISH (PathVysion (R), Abbot/Vysis) technique and the automated silver in situ hybridization (SISH, INFORM (TM), Ventana) technique. For comparison, all the specimens were stained by immunohistochemistry (Ventana-PATHWAY (R) 4B5). Evaluation was performed by two pathologists and with following the instructions of the manufacturers and the guidelines of the American Society of Clinical Oncology/College of American Pathologists. Results: The results of SISH and FISH were identical in all 58 cases; 17 cases showed HER2 amplification, and on the other hand, 41 cases didn't show HER2 amplification. Five weakly positive (2+) cases in immunohistochemistry staining revealed one HER2 amplification and four no HER2 amplification on both SISH and FISH. The SISH results of the HER2/CEP17 ratio were well correlated with the FISH results of the HER2/CEP17 ratio (correlation coefficient r=0.745, Linear regression r(2)=0.555, p<0.001). Conclusion: The results of the SISH technique for assessing the HER2 status of excised breast carcinoma is comparable to the result obtained by FISH. However, SISH has the advantage of having permanent end result that can be visualized by an ordinary light microscope and less laborious preparation and time is needed than is required by FISH. SISH seems to be more feasible than FISH for assessing HER2 amplification of breast cancer.