Silver In Situ Hybridization (SISH) For Determination of HER2 Gene Status in Breast Carcinoma

Abstract

The importance of HER2 status in breast cancer management has focused attention on the ability of clinical assays to correctly assign HER2 amplification status. There is no consensus as to the best method for assessing HER2 status. Disadvantages of fluorescence in situ hybridization (FISH) testing include longer time required for staining and scoring slides, requirements for specialized training and fluorescence microscopy, and loss of the signal due to quenching of the fluorescent dye. Silver-enhanced in situ hybridization (SISH) is a rapid fully automated assay providing permanently stained slides that are interpreted by conventional bright field microscopy which enables pathologists to evaluate slides within the context of tissue morphology. This study evaluates the concordance between SISH and FISH assays in determining the status of HER2 gene amplification in a cohort of 298 primary invasive breast carcinomas. Furthermore, we assessed in detail the variables contributing to interobserver interpretive reproducibility of HER2 SISH among 10 pathologists. HER2 was quantified using the ratio of HER2 to CHR17 signals using the conventional historical interpretation scale and also by the American Society of Clinical Oncology/College of American Pathologists reporting scheme. For SISH status determined by consensus among 10 pathologists, overall concordance between SISH and FISH was identified in 288 of 298 cases (96.6%) using the conventional Food and Drug Administration approved criteria. Overall agreement was observed in 282 of 285 cases (98.9%) using the American Society of Clinical Oncology/College of American Pathologists result reporting scheme (with equivocal cases removed). In conclusion, SISH represents a novel approach for the determination of HER2 status in breast cancer. The overall concordance between SISH and FISH is excellent, and the interpretation of SISH results by pathologists is most reproducible using the HER2/CHR17 ratio.

Accuracy of HER2 status determination on breast core-needle biopsies (immunohistochemistry, FISH, CISH and SISH vs FISH)

“…These results are consistent with previous data available on surgical specimens. [12][13][14]33 In conclusion and based on our results, immunohistochemistry status assessed on cores biopsy is highly concordant with FISH in cores and surgical specimens. Furthermore, CISH and/or SISH even represents a safe alternative method to determine HER2 status on these cores biopsies to confirm any ambiguous immunohistochemistry results (2 þ ) or to perform HER2 status screening, if ISH is used as first-line screening method.…”

“…[8][9][10][11] SISH was implemented more recently and three studies reported a 97, 96 and 87% concordance between SISH and FISH results on excision samples [12][13][14] taking into account that discordant cases could be partly explained by intratumor heterogeneity of amplification. One study showed an 89% concordance of SISH results between surgical specimens and core-needle biopsies but the number of studied cases was limited (n ¼ 56).…”

Determination of HER2 Gene Amplification in Breast Cancer using Dual-color Silver Enhanced in situ Hybridization (dc-SISH) and Comparison with Fluorescence ISH (FISH)

“…Until now, some studies have been performed to compare FISH and SISH methods with a correlation ratio of 89-98% (Dietel et al, 2007;Carbone et al, 2008;Papouchado et al, 2010;Ying et al, 2010;Park et al, 2011;Lee et al, 2012;Tvrdík et al, 2012). A correlation ratio of 92.3% was found in this study between FISH and SISH.…”

“…Pre-analytic factors affect the test results less than immunohistochemistry. Nevertheless, the FISH technique is more expensive, it necessitates special equipment and educated personnel, its application process lasts longer, and a fluorescent microscope is required for the evaluation of the test (Francis et al, 2009;Papouchado et al, 2010;Ying et al, 2010;Arnould et al, 2012;Schiavon et al, 2012). The SISH method, which can be an alternative to the FISH technique, is comprised of a multimer technology, combined with enzyme metallography, which allows for the identification of the HER2 oncogene amplification with silver marking.…”

“…Spot-like fluorescent signals are evaluated under highly sensitive fluorescent microscopes in the FISH method; while shining opaque silver is easily seen under the light microscope in the SISH method. Moreover, the results can be evaluated quickly and histopathological evaluation of the same tissue section can be performed at the same time (Francis et al, 2009;Papouchado et al, 2010;Ying et al, 2010;Lee et al, 2012;Schiavon et al, 2012).…”