Chromogenic in situ hybridization: a multicenter study comparing silver in situ hybridization with FISH

Comparison of Dual-ISH (DISH) With Fluorescence In Situ Hybridization (FISH) and Correlation With Immunohistochemical Findings for HER2/Neu Status in Breast Carcinoma

INTRODUCTION

The most widely used methods for determination of HER2/neu status in breast carcinoma are immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH). Both techniques are associated with technical and interpretive difficulties. Alternative methods exist including quantitative PCR and the newly developed chromogenic dual in situ hybridization (DISH).

METHODS

We evaluated HER2 DISH as an alternative to FISH and report our findings from 101 cases. In addition, we correlated HER2 DISH and FISH results with HercepTest and 4B5 immunohistochemistry.

RESULTS

Eight cases failed FISH analysis and none failed DISH analysis. A 95% (88/93) concordance was found between DISH and FISH for all cases in the series. When only 2+ IHC cases were evaluated, the concordance was 94% for DISH and FISH. Using the 2013 ASCO/CAP recommendations, none of the tested cases were equivocal by FISH or DISH despite 66% of cases being 2+ by HercepTest and 32% by the 4B5 antibody.

COMMENT

Our study, which utilizes a majority of IHC equivocal cases, demonstrates that HER2 FISH and DISH are concordant methodologies. HER2 DISH is therefore an acceptable alternative to FISH.

What to expect from the 2018 ASCO/CAP HER2 guideline in the reflex in situ hybridization test of immunohistochemically equivocal 2+ cases?

To evaluate the effect of the 2018 ASCO/CAP guideline in the identification of HER2-positive breast carcinomas (BC) in reflex in situ hybridization (ISH) test. A total of 592 primary invasive BC cases from before and after the publication of the updated ASCO/CAP guideline were evaluated for HER2 amplification by silver ISH according to the 2013 and 2018 guidelines. Cases were mostly (95%) HER2 equivocal by immunohistochemistry (IHC), not centrally reviewed. Other reasons for referring cases were IHC confirmation, IHC discordancy (either between needle-core-biopsy (NCB) and surgical excision specimen (SES) or between different laboratories) and IHC result unexpected for histopathologic features. Cases evaluated with the 2013 guideline (1st cohort) were 14.6% HER2-positive, decreasing significantly after the reclassification with the 2018 guideline due to the exclusion of group 2 cases without HER2 protein overexpression. Cases studied after the implementation of the 2018 guideline (2nd cohort) were 8.7% HER2-positive, a frequency that was not significantly different from the reclassification of the 1st cohort with the 2018 guideline. All cases referred for IHC confirmation had the expected ISH result. Cases with IHC discordancy between NCB and SES were ISH concordant. Only one out of 14 cases with an IHC score 3+ and classified as histological grade 1 or with a Ki67 below 10% was classified as ISH HER2-positive. The 2018 ASCO/CAP guideline resulted in a decrease of HER2-positive cases in reflex ISH test, selecting less patients for anti-HER2-targeted therapy.

Comparison of HER2 status determination methods in HER2 (2+) patients: Manual fluorescent in situ hybridization (FISH) vs. dual silver enhanced in situ hybridization (SISH)

HER2 amplification has been demonstrated in 15-25% of invasive breast carcinomas and can be assessed using immunohistochemical and in situ hybridization methods. Here, we compared the accuracy of dual SISH to manual FISH in HER2 (2+) breast carcinoma and evaluated the feasibility of dual SISH method in routine practice. Sixty HER2 (2+) consecutive tumor samples diagnosed between January 2009 and February 2013 were selected. Demographic, histological and immunohistochemical features and FISH results were recruited from patient records and compared to dual SISH results. Nine (15%) of the 60 tumor samples were excluded from statistical analysis due to lack of interpretable SISH signals. HER2 staining percentages by immunohistochemistry differed between 20 and 80%. HER2 amplification was shown in 7 (13.7%) and 8 (15.7%) patients by FISH and SISH, respectively. Very good agreement was observed between FISH and SISH methods (kappa value: 0.92). Significant correlation was found between HER2 staining percentage and FISH positivity, in contrast to SISH positivity (p=0.012 vs. p=0.069). Our results are consistent with previously reported literature, indicating SISH can be used to determine HER2 status. However, preanalytical and analytical problems may cause inadequate or uncountable signals, making interpretation impossible for the pathologist and highlighting the importance of standardization and quality control programs.

Application of the 2013 ASCO/CAP guideline and the SISH technique for HER2 testing of breast cancer selects more patients for anti-HER2 treatment

The aim of this study is to assess the impact of changes of the 2013 ASCO/CAP guideline on the results of HER2 testing in breast cancer. A series of 916 primary invasive breast cancer cases, assessed as HER2 2+ by IHC in part using the 2007 and in part the 2013 ASCO/CAP criteria, was evaluated for HER2 amplification status by SISH and classified according to both 2007 and 2013 ASCO/CAP ISH guideline criteria. We observed a significant increase of HER2-positive cases (12.4 to 16.8%) and a decrease of HER2-equivocal cases (3.6 to 0.7%). Of the cases studied, 52.1% fulfilled both criteria of HER2/CEP17 ratio and average HER2 copy number per cell to be classified as HER2-positive. Reclassification of the cases from before the introduction of the new ASCO/CAP guideline with the 2013 ISH criteria resulted in an increase of cases with a HER2-positive status (12.4 to 14.2%) and in a decrease of HER2-equivocal cases (3.6 to 1.6%). The 2013 ASCO/CAP guideline selects more patients for anti-HER2 targeted therapy, mostly based on the modifications of criteria to evaluate ISH-HER2.

Advantages and disadvantages of technologies for HER2 testing in breast cancer specimens

OBJECTIVES

Human epidermal growth factor receptor 2 (HER2) plays a central role as a prognostic and predictive marker in breast cancer specimens. Reliable HER2 evaluation is central to determine the eligibility of patients with breast cancer to targeted anti-HER2 therapies such as trastuzumab and lapatinib. Presently, several methods exist for the determination of HER2 status at different levels (protein, RNA, and DNA level).

METHODS

In this review, we discuss the main advantages and disadvantages of the techniques developed so far for the evaluation of HER2 status in breast cancer specimens.

RESULTS

Each technique has its own advantages and disadvantages. It is therefore not surprising that no consensus has been reached so far on which technique is the best for the determination of HER2 status.

CONCLUSIONS

Currently, emphasis must be put on standardization of procedures, internal and external quality control assessment, and competency evaluation of already existing methods to ensure accurate, reliable, and clinically meaningful test results. Development of new robust and accurate diagnostic assays should also be encouraged. In addition, large clinical trials are warranted to identify the technique that most reliably predicts a positive response to anti-HER2 drugs.

Quantification of HER family receptors in breast cancer

The clinical success of trastuzumab in breast cancer taught us that appropriate tumor evaluation is mandatory for the correct identification of patients eligible for targeted therapies. Although HER2 protein expression by immunohistochemistry (IHC) and gene amplification by fluorescence in situ hybridization (FISH) assays are routinely used to select patients to receive trastuzumab, both assays only partially predict response to the drug. In the case of epidermal growth factor receptor (EGFR), the link between the presence of the receptor or its amplification and response to anti-EGFR therapies could not be demonstrated. Even less is known for HER3 and HER4, mainly due to lack of robust and validated assays detecting these proteins. It is becoming evident that, besides FISH and IHC, we need better assays to quantify HER receptors and categorize the patients for individualized treatments. Here, we present the current available methodologies to measure HER family receptors and discuss the clinical implications of target quantification.

HER2 assessment by silver in situ hybridization: where are we now?

HER2 testing in breast and gastric cancer is critical not only as a prognostic tool but also as a predictive marker for response to the humanized monoclonal antibody trastuzumab. Currently, HER2 status is assessed on histological and cytological specimens by conventional validated methods such as immunohistochemistry and FISH, while bright-field in situ hybridization techniques, such as silver in situ hybridization and chromogenic in situ hybridization, may offer performance benefits over FISH. The major points are first, technical issues, advantages and disadvantages relevant to each methods, and their clinical implications and second, the well-known genetic heterogeneity of HER2, and the occurrence of polysomy of chromosome 17. This review aims to summarize the growing body of literature on the accuracy of bright-field in situ techniques, notably silver in situ hybridization, in assessing HER2 status, and to discuss the role of such methods in pathology practice.

Bright-field HER2 dual in situ hybridization (DISH) assay vs fluorescence in situ hybridization (FISH): focused study of immunohistochemical 2+ cases

OBJECTIVES

To compare the INFORM HER2 bright-field dual in situ hybridization (DISH) DNA probe cocktail assay with the PathVysion fluorescence in situ hybridization (FISH) assay on 103 invasive breast carcinomas with a 2+ score on immunohistochemistry (IHC).

METHODS

The cases were categorized as positive, equivocal, or negative for HER2 gene amplification using the 2007 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) HER2:CEP17 ratio criteria and also based on mean HER2 gene copies/cell. The third criterion used a HER2:CEP17 ratio of 2 to categorize cases as positive or negative.

RESULTS

The agreement between FISH and DISH was 85% using the 2007 ASCO/CAP ratio criterion, 79% using the mean HER2 gene copies/cell criterion, and 92% using the 2.0 cutoff HER2:CEP17 ratio criterion. In addition, 20 known IHC 3+ breast carcinomas analyzed by DISH showed clusters of the HER2 gene consistent with unequivocal amplification.

CONCLUSIONS

Despite some technical and interpretational issues associated with DISH, it compares favorably with FISH in this group of challenging breast cancer cases.

Chromogenic in situ hybridization compared with other approaches to evaluate HER2/neu status in breast carcinomas

Human epidermal growth factor receptor 2 (HER2) has been evaluated in breast cancer patients to identify those most likely to benefit from herceptin-targeted therapy. HER2 amplification, detected in 20-30% of invasive breast tumors, is associated with reduced survival and metastasis. The most frequently used technique for evaluating HER2 protein status as a routine procedure is immunohistochemistry (IHC). HER2 copy number alterations have also been evaluated by fluorescence in situ hybridization (FISH) in moderate immunoexpression (IHC 2+) cases. An alternative procedure to evaluate gene amplification is chromogenic in situ hybridization (CISH), which has some advantages over FISH, including the correlation between HER2 status and morphological features. Other methodologies have also been used, such as silver-enhanced in situ hybridization (SISH) and quantitative real-time RT-PCR, to determine the number of HER2 gene copies and expression, respectively. Here we will present a short and comprehensive review of the current advances concerning HER2 evaluation in human breast cancer.

Comparison of dual-color dual-hapten brightfield in situ hybridization (DDISH) and fluorescence in situ hybridization in breast cancer HER2 assessment

The most optimal method for assessing HER2 status is still subject to controversy as far as the type of assay used, the optimal method to perform, and the costs of each assay are concerned. The current study was done as a validation study prior to setting up a clinical HER2 testing service using the new commercial dual-color dual-hapten brightfield in situ hybridization (DDISH), but it was felt that our experience may be of interest to other laboratories considering setting up HER2 diagnostic facilities. One hundred and five patients diagnosed with invasive breast cancer were selected. PathVysion FISH and DDISH assays were carried out. Concordance correlation coefficients showed near perfect agreement in average HER2 and centromere-specific signal counts per cell and in HER2/CEN17 ratios between the PathVysion and the DDISH assays, and also the Kappa measure showed near perfect agreement between the two assays (Kappa=0.8712, P<0.0001). Statistical analysis confirmed that the two assays are comparable in terms of detection of HER2 gene amplification and suggests its utilization in routine HER2 diagnostics.

Comparison of fluorescence in situ hybridization (FISH) and dual-ISH (DISH) in the determination of HER2 status in breast cancer

The determination of HER2 amplification is critical to selecting appropriate patients for HER2 targeted therapy in breast cancer. Dual in situ hybridization (DISH), an alternative to fluorescence in situ hybridization (FISH) and immunohistochemistry, is now available. To compare the FISH and DISH methods, we tested 251 samples enriched for common or difficult-to-assess HER2 anomalies. Seven samples failed DISH testing. There was a 64% (156/244) concordance between FISH and DISH by anomaly (κ = 0.58, 95% confidence interval, 0.51-0.65; P < .0001) and an 83% (203/244) concordance by amplification status (κ = 0.58; 95% confidence interval, 0.47-0.69; P < .0001). DISH resulted in lower estimates of HER2/ centromere 17 ratios than FISH, and many cases that were equivocal with FISH were normal with DISH. DISH did not detect any case with coamplification of HER2 and centromere 17. Using a cohort of difficult specimens, we observed less than 95% concordance between FISH and DISH. DISH may underestimate the HER2/chromosome 17 ratio, or FISH may overestimate this ratio.

Simultaneous analysis of HER2 gene and protein on a single slide facilitates HER2 testing of breast and gastric carcinomas

This study sought to evaluate a new combined gene and protein detection platform in the context of HER2 evaluation in breast and gastric carcinomas. HER2 immunohistochemistry (IHC) and dual color in situ hybridization (Dual ISH) were combined on a single slide. Results were compared with conventional HER2 IHC and fluorescence ISH. Results from the gene and protein assay were reliable and highly reproducible for both breast and gastric carcinomas. Concordance was found between conventional HER2 IHC and ISH testing and the gene and protein assay in the same laboratory (>95% for Dual ISH; lower for IHC because of different antibody clones), between IHC and Dual ISH performed on the same slide (>92%), and in the gene and protein assays between laboratories (>96%). This cost- and time-effective method provides fast and definitive results (IHC confirmed by means of Dual ISH) to aid in rapid treatment decisions. It can also be applied to other gene and protein combinations.

Improved method of detecting the ERG gene rearrangement in prostate cancer using combined dual-color chromogenic and silver in situ hybridization

The recently detected TMPRSS2-ERG fusion gene was revealed as a recurrent and prevalent prostate cancer (PCa)-specific event, potentially qualifying it for clinical use. To detect this alteration, fluorescence in situ hybridization (FISH) is the method of choice. However, FISH has some disadvantages for widespread adoption in clinical practice. Subsequently, chromogenic in situ hybridization, which uses organic chromogens, and enzymatic metallography silver in situ hybridization have emerged as promising bright-field alternatives. Compared with chromogenic in situ hybridization, silver in situ hybridization signals are very distinct and superior with regard to signal clarity and resolution, but the method excludes multicolor protocols. Based on the ERG break-apart FISH assay, we established a dual-color ERG break-apart assay using combined chromogenic in situ hybridization and silver in situ hybridization (CS-ISH) and compared these results with those obtained by FISH. We assessed 178 PCa and 10 benign specimens for their ERG rearrangement status by applying dual-color FISH and CS-ISH ERG break-apart assays to consecutive sections. We observed a highly significant concordance (97.7%) between FISH- and CS-ISH-based results (Pearson's correlation coefficient = 0.955, P < 0.001). Our findings demonstrate that the ERG rearrangement status can reliably be assessed by CS-ISH. Further, the CS-ISH technique combines the accuracy and precision of FISH with the ease of bright-field microscopy. This tool allows a much broader spectrum of applications in which to study the biological role and clinical use of ERG rearrangements in PCa.

Detection of ALK gene rearrangement in non-small cell lung cancer: a comparison of fluorescence in situ hybridization and chromogenic in situ hybridization with correlation of ALK protein expression

INTRODUCTION

Accurate determination of ALK rearrangement is important in lung cancer patients, especially in determining their eligibility for crizotinib therapy. Fluorescence in situ hybridization (FISH) has been regarded as the gold standard method for detecting ALK rearrangement. However, FISH requires a fluorescence microscope, and the signals are labile and rapidly fade over time. This study evaluates the concordance between ALK gene rearrangement in non-small cell lung cancer assessed by ALK FISH and a newly developed ALK chromogenic in situ hybridization (CISH) and correlates the results with ALK protein expression assessed by immunohistochemistry.

METHODS

A total of 465 formalin-fixed, paraffin-embedded non-small cell lung cancer samples were analyzed by ALK FISH (PathVysion, Vysis, Abbott) and ALK CISH. For comparison, all specimens were stained by immunohistochemistry (clone 5A4, Novocastra) and interobserver reproducibility was assessed.

RESULTS

We found that agreement between the pathologists on the CISH-determined ALK status was achieved in 449 patients (96.6%), and ALK rearrangement was identified in 18 patients (4.0%) in CISH method. Among these cases, 443 cases (95.3%) had results matching the corresponding FISH results: 17 rearranged, 425 wild types, and 1 discordant case. There was high concordance in the assessment of ALK gene rearrangement between FISH and CISH techniques (κ = 0.92) and between observers (κ = 0.97). In addition, there was high concordance in the ALK gene status and ALK protein expression between CISH and IHC tests (κ = 0.82).

CONCLUSIONS

CISH is a highly reproducible and practical method to detect ALK gene rearrangement and correlated well with ALK protein expression. Here, we present a diagnostic algorithm (Chung's SNUBH ALK protocol) to detect lung cancer with ALK rearrangements using IHC, FISH and CISH. Because CISH allows a concurrent analysis of histological features of the tumors and gene rearrangement, it appears to be a useful method in determining ALK gene rearrangement.

Hybridization for human epidermal growth factor receptor 2 testing in gastric carcinoma: a comparison of fluorescence in-situ hybridization with a novel fully automated dual-colour silver in-situ hybridization method

Aims:

Amplification of the human epidermal growth factor receptor 2 (HER2) gene has been reported in gastric carcinoma (GC). Accordingly, trastuzumab plus chemotherapy has recently become the new standard treatment for HER2-positive advanced GCs. The aim was to compare the alleged gold standard for hybridization [fluorescence in-situ hybridization (FISH)] with a novel, fully automated brightfield dual-colour silver-enhanced in-situ hybridization (SISH) method.

Methods and results:

The studies series was comprised of 166 GC samples. Additionally, tumours with discordant results obtained by FISH and SISH were analysed by real-time quantitative polymerase chain reaction (PCR) with the LightMix kit HER-2/neu. Of the samples, 17.5% and 21% were amplified by FISH and SISH, respectively. Heterogeneity was identified in up to 52% of cases. In 96.4% of cases, FISH showed the same results as SISH. All six discordant cases were positive by SISH and negative by FISH. On review of the FISH slides, all contradictory cases were polysomic and were confirmed to be negative for amplification by real-time PCR. Interestingly, all ratios in this latter group were between 2.06 and 2.50, so setting the cut-off for amplification at ≥3 resulted in perfect concordance.

Conclusions:

Dual-colour SISH represents a novel method for the determination of HER2 status in GC.

The human epidermal growth factor receptor 2 (HER2)

The declared "war on cancer" aimed to eradicate this disease using our knowledge of cancer cell biology to develop novel therapeutics. One such target of these novel therapies has been the human epidermal growth factor receptor 2 (HER2) gene. Unique in the approach to abolishing function of this gene coded receptor, it was the first target of new monoclonal antibody therapy targeting the extracellular receptor and now also a target of small molecule drugs against the intracellular tyrosine kinase domain. In this instance, it was also one of the first applications of personalized medicine requiring companion diagnostics. In this manuscript, we review the biology and clinical applications of HER2 as a biomarker of disease and as a therapeutic target.

HER2 status in operable breast cancers from Vietnamese women: Analysis by immunohistochemistry (IHC) and automated silver enhanced in situ hybridization (SISH)

BACKGROUND

HER2 amplification has been reported to occur in 19-30% of breast cancers in women from Western countries. Little is known about the HER2 status in breast cancers from Vietnamese women. The aim of this study was to assess the HER2 status in Vietnamese women with operable breast cancer using immunohistochemistry and silver in situ hybridization techniques.

MATERIAL AND METHOD

Tissue blocks from 242 Vietnamese women with invasive primary breast carcinoma were stained by immunohistochemistry (IHC) and a dual silver in situ hybridization (SISH) for assessing HER2 status. The analysis followed international recommendations with a semi-quantitative grading of the reaction in four levels, "0", "1+", "2+" and "3+". The HER2 gene amplification was assessed by calculating the ratio of HER2/chromosome 17 in 20 tumor cell nuclei. A ratio of <1.8 was classified as non-amplification and a ratio >2.2 indicated tumors with gene amplification. A ratio between 1.8 and 2.2 was equivocal.

RESULTS

Using IHC, 39% of the tumors strongly expressed "3+" the HER2 protein. An intermediate level "2+" of the protein was found in 11% while 50% showed no or low "0/1+" levels of protein expression. Gene amplification was found in 95% and 46% of the tumors with high "3+" and intermediate "2+" levels of protein expression, respectively. Thus, 41% of the patients had tumors with HER2 amplification. The concordance between IHC and SISH was 87%. Gene amplification was more frequent in ER negative than in ER positive tumors, 57% versus 33%, respectively. Additionally, tumors from postmenopausal women were amplified in 55% as compared to 36% in premenopausal women.

CONCLUSIONS

HER2 gene amplification was found in 41% of Vietnamese breast cancers; this level is considerably higher than that previously found in a series of Swedish breast cancer women. The HER2-positive tumors were more often found in post-menopausal women than in ER negative tumors.

Current technologies for HER2 testing in breast cancer

BACKGROUND

Molecular techniques play an increasingly important role in breast cancer detection and help in the prediction of prognosis and treatment response. HER-2/neu predicts the sensitivity of breast tumors to trastuzumab and lapatinib. Presently there are several ways to assess HER2 status at the protein level (e.g. ELISA), at the RNA level (RT-PCR, microarray) and at the DNA level (fluorescence in situ hybridization, chromogenic in situ hybridization (ISH), silver in situ hybridization or multiplex ligation-dependent probe amplification).

DESIGN

This paper provides an overview of new developments in HER2 testing.

RESULTS

Although these techniques correlate well in comparative studies, discrepancies remain. Each technique has its own (dis)advantages and thus there is no real gold standard. Not surprisingly, there is no consensus at present on which of the protein- or gene-based techniques is superior, on the use of mono- or duo-probe ISH systems, nor on the use of manual or fully-automated staining- and scoring systems.

CONCLUSION

Until large clinical trials clearly point out one strategy as the best predictive one for trastuzumab response, the choice for a testing strategy will probably be based on local preferences which consider both practical and economic issues. Standardization, proper internal and external quality control assessment, laboratory accreditation and automation of tissue processing (autostainers) and interpretation methods (image analysis) will play an increasingly important role in HER2 testing.

A UK NEQAS ISH multicenter ring study using the Ventana HER2 dual-color ISH assay

We performed a multicenter assessment of a new HER2 dual-color chromogenic in situ hybridization (CISH) test and herein report on concordance of CISH data with fluorescence in situ hybridization (FISH) data and intraobserver and interlaboratory scoring consistency. HER2 results were evaluated using duplicate cores from 30 breast cancers in 5 laboratories using the Ventana HER2 dual-color ISH assay (Ventana Medical Systems, Cambridgeshire, England) and in 1 central laboratory using a standard FISH assay. Overall 93.3% of cases were successfully analyzed by CISH across the 5 participating laboratories. There was excellent concordance (98.0% overall) for diagnosis of HER2 amplification by CISH compared with FISH. Intraobserver variability (7.7%) and intersite variability (9.1%) of absolute HER2/chromosome enumeration probe 17 ratios were tightly controlled across all participating laboratories. The Ventana HER2 dual-color ISH assay is robust and reproducible, shows good concordance with a standard FISH assay, and complies with requirements in national and international guidelines for performance of ISH-based diagnostic tests.

Traditional molecular markers and response to adjuvant endocrine or trastuzumab-based therapies

PURPOSE OF REVIEW

The accurate assessment of traditional molecular markers is essential to inform the choice of the adjuvant systemic treatments for patients with breast cancer. Extensive research efforts have been made to explore whether it is also possible to predict the actual response to the different therapeutic options based on the expression of these markers.

RECENT FINDINGS

Endocrine responsiveness of breast cancer has been eventually defined according to the expression of estrogen receptors in at least 1% of invasive tumor cells. The quantitative evaluation of estrogen receptors, progesterone receptors (PgR) and Ki-67 labeling index may help in selecting patients with estrogen receptor-positive and HER2-negative tumors who can be spared or may benefit from the addition of chemotherapy to endocrine therapy. Guideline recommendations for an optimal testing of estrogen receptors and PgR have been issued to assist pathologists in the accurate assessment of these markers. Progress has also been made in the identification of candidate patients to HER2-targeted therapies and in the prediction of response to trastuzumab.

SUMMARY

Traditional molecular markers play a major role in the selection of candidate patients to systemic interventions, but they are of limited value in predicting their actual response to the different treatments, especially when the markers are evaluated individually.

Silver in situ hybridization (SISH) for determination of HER2 gene status in breast carcinoma: comparison with FISH and assessment of interobserver reproducibility

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.

Out of the darkness and into the light: bright field in situ hybridisation for delineation of ERBB2 (HER2) status in breast carcinoma

Assessment of ERBB2 (HER2) status in breast carcinomas has become critical in determining response to the humanised monoclonal antibody trastuzumab. The current joint College of American Pathologists and the American Society of Clinical Oncology guidelines for the evaluation of HER2 status in breast carcinoma involve testing by immunohistochemistry and fluorescence in situ hybridisation (FISH). However, neither of these modalities is without limitations. Novel bright field in situ hybridisation techniques continue to provide viable alternatives to FISH testing. While these techniques are not limited to evaluation of the HER2 gene, the extensive number of studies comparing bright field in situ techniques with other methods of assessing HER2 status allow a robust evaluation of this approach. Analysis of the literature demonstrates that, when used to assess HER2 gene status, bright field in situ hybridisation demonstrates excellent concordance with FISH results. The average percentage agreement in an informal analysis of studies comparing HER2 amplification by chromogenic in situ hybridisation with FISH was 96% (SD 4%); kappa coefficients ranged from 0.76 to 1.0. Although a much smaller number of studies are available for review, similar levels of concordance have been reported in studies comparing HER2 amplification by methods employing metallography (silver in situ hybridisation) with FISH. A summary of the advancements in bright field in situ hybridisation, with focus on those techniques with clinical applications of interest to the practicing pathologist, is presented.