Metallographic in situ hybridization

Review of In Situ Hybridization (ISH) Stain Images Using Computational Techniques

Recent advancements in medical imaging have greatly enhanced the application of computational techniques in digital pathology, particularly for the classification of breast cancer using in situ hybridization (ISH) imaging. HER2 amplification, a key prognostic marker in 20-25% of breast cancers, can be assessed through alterations in gene copy number or protein expression. However, challenges persist due to the heterogeneity of nuclear regions and complexities in cancer biomarker detection. This review examines semi-automated and fully automated computational methods for analyzing ISH images with a focus on HER2 gene amplification. Literature from 1997 to 2023 is analyzed, emphasizing silver-enhanced in situ hybridization (SISH) and its integration with image processing and machine learning techniques. Both conventional machine learning approaches and recent advances in deep learning are compared. The review reveals that automated ISH analysis in combination with bright-field microscopy provides a cost-effective and scalable solution for routine pathology. The integration of deep learning techniques shows promise in improving accuracy over conventional methods, although there are limitations related to data variability and computational demands. Automated ISH analysis can reduce manual labor and increase diagnostic accuracy. Future research should focus on refining these computational methods, particularly in handling the complex nature of HER2 status evaluation, and integrate best practices to further enhance clinical adoption of these techniques.

Gene expression detection in developing mouse tissue using in situ hybridization and µCT imaging

High resolution and noninvasiveness have made soft-tissue X-ray microtomography (µCT) a widely applicable three-dimensional (3D) imaging method in studies of morphology and development. However, scarcity of molecular probes to visualize gene activity with µCT has remained a challenge. Here, we apply horseradish peroxidase-assisted reduction of silver and catalytic gold enhancement of the silver deposit to in situ hybridization in order to detect gene expression in developing tissues with µCT (here called GECT, gene expression CT). We show that GECT detects expression patterns of collagen type II alpha 1 and sonic hedgehog in developing mouse tissues comparably with an alkaline phosphatase-based detection method. After detection, expression patterns are visualized with laboratory µCT, demonstrating that GECT is compatible with varying levels of gene expression and varying sizes of expression regions. Additionally, we show that the method is compatible with prior phosphotungstic acid staining, a conventional contrast staining approach in µCT imaging of soft tissues. Overall, GECT is a method that can be integrated with existing laboratory routines to obtain spatially accurate 3D detection of gene expression.

Changes in breast cancer staging trends among Egyptian women after COVID-19: A retrospective single-center study

OBJECTIVES

Since being declared a global pandemic, the SARS-CoV-2 virus had a significant impact on the entire globe. The pandemic has placed a heavy burden on healthcare systems worldwide, and cancer patients are particularly prone. Despite the fact that initial international reports suggest delays in breast cancer (BC) diagnosis and screening programs, the Egyptian context requires additional research on this topic. To examine whether COVID-19 has changed the pattern of disease presentation before and after the pandemic, focusing on the tumor, node, and metastasis (TNM) staging of the disease at the initial presentation.

METHODS

This single-center, retrospective study of female BC patients initially diagnosed at Baheya Foundation was conducted during the following time frames: from Jan 2019 to Jan 2020 (Pre COVID-19 cohort) and from Mar 2020 to Mar 2021 (post-COVID-19 cohort). We compared the two cohorts in terms of clinical characteristics, tumor characteristics, and the number of days from presentation to treatment. Our primary endpoint was the difference in the TNM stage of BC at the initial presentation.

RESULTS

This analysis included 710 BC patients, 350 from the pre-COVID cohort and 360 from the post-COVID group. We detected a 27.9% increase in late-stage BC (stages III-IV) in the post-pandemic cohort compared to the pre-pandemic (60.1% vs. 47%, p < 0.001). The time from diagnosis to commencement of treatment was significantly longer (28.34 ± 18.845 vs 36.04 ± 23.641 days, p < 0.001) in the post-COVID cohort (mean difference = 7.702, 95% CI 4.54-10.85, p < 0.001). A higher percentage of patients in the post-pandemic cohort received systemic neoadjuvant therapy (p-value for Exact's test for all treatment options = 0.001).

CONCLUSIONS

The number of patients requiring systemic neoadjuvant chemotherapy increased dramatically in the post-pandemic group with advanced stages of BC at presentation. This study highlights the need for proper management of cancer patients during any future pandemic.

Advances in HER2 testing

HER2-positive breast cancer is a particularly aggressive type of breast cancer. Indication of HER2 positivity is essential for its treatment. In addition to a few FDA-approved methods such as immunohistochemical (IHC) detection of HER2 protein expression and in situ hybridization (ISH) assessment of HER2 gene amplification, several novel methods have been developed for HER2 testing in recent years. This chapter provides an overview of HER2 testing with emphasis on those new methods.

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.

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.

Validation and workflow optimization of human epidermal growth factor receptor 2 testing using INFORM HER2 dual-color in situ hybridization

Human epidermal growth factor receptor 2 (HER2) status is useful for predicting response to trastuzumab. Fluorescence in situ hybridization (FISH) for HER2 gene amplification is accurate but limited because of cost, the need for fluorescence microscopy, the limited assessment of histology, and the fading of its signal over time. Dual-color in situ hybridization (Dual ISH) is fully automated, is viewable by bright-field microscopy, has a stable signal, and has separate colors for HER2 and chromosome 17 signals. HER2 immunohistochemistry (IHC), FISH, and Dual ISH were performed on 101 breast cancer cases. Sixteen of 17 cases with 3+ HER2 by IHC showed gene amplification by FISH, and 15 showed amplification by Dual ISH. Three of the 2+ IHC cases were either amplified or equivocal by Dual ISH. None of the IHC-negative cases were amplified by either FISH or Dual ISH. Dual ISH agreed with FISH in 93% of cases. Among the 6 discrepancies, 4 were for an equivocal result for 1 test compared with either a positive or a negative result for the other test. The average differences in readings between Dual ISH and FISH in the discrepant cases were only 0.02, with a range of -1.37 to 1.85. Turnaround time for FISH as a send-out test from test ordering to reporting averaged 8.27 workdays, whereas the turnaround time for Dual ISH performed in-house averaged 4.94 workdays (P < .0000001). Our results indicated that automated Dual ISH is a useful method for evaluating HER2 status in a clinical setting.

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.

Effectiveness of silver-enhanced in situ hybridization for evaluating HER2 gene status in invasive breast carcinoma: a comparative study

BACKGROUND AND AIMS

HER2 gene amplification occurs in breast cancers and has implications for treatment and prognosis. Recently, a new direct evaluation technique, silver enhanced in situ hybridization (SISH) was developed for evaluating HER2 gene status. This study was performed to evaluate the SISH technique for clinical use by comparing it to that of fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC).

METHODS

We studied 543 cases of excised breast specimens diagnosed as invasive ductal carcinoma by IHC, FISH, and SISH using a tissue microarray. IHC, FISH, and SISH results were interpreted according to the American Society of Clinical Oncology/College of American Pathologists guidelines. A total of seven English studies that reported the concordance rates of SISH and BDISH compared to FISH published before July 2011 were retrieved.

RESULTS

The consensus concordance rate between SISH and FISH was 96.69% (kappa value = 0.9175). The pooled sensitivity was 0.94 [95% confidence interval (CI) = 0.91-0.97], and the pooled specificity was 0.98 (95% CI = 0.96-099) in a meta-analysis of the retrieved studies and this study. Area under the receiver operating characteristics curve was 0.9906.

CONCLUSIONS

SISH technique is an effective modality and is comparable with FISH for evaluating HER2 gene amplification in patients with breast carcinoma.

Silver-Enhanced In Situ Hybridization as an Alternative to Fluorescence In Situ Hybridization for Assaying HER2 Amplification in Clinical Breast Cancer

Purpose

Valid determination of HER2 status is a prerequisite to establish an adequate treatment strategy for breast cancer patients, regardless of the disease stage. The goal of this study was to examine the feasibility of the newly developed silver-enhanced in situ hybridization (SISH) technique as an alternative to fluorescence in situ hybridization (FISH) for HER2 assay in primary invasive breast cancer.

Methods

FISH and SISH for HER2 amplification were performed using tissue microarray. Both methods were used in 257 consecutive primary breast cancers.

Results

HER2 amplification was observed in 62 (23.1%) of a total of 257 breast cancers based on SISH. Of the 257 breast cancers measured using both methods, the results of the two methods were consistent in 248 (concordance, 96.5%; kappa=0.903). When we compared HER2 amplification in the primary tumor with the metastatic lymph nodes of the same patients, HER2 amplification was observed in nine cases (14.0%) out of 64 cases in which HER2 was not amplified in the primary tumors. In contrast, HER2 status was completely preserved in metastatic lymph nodes showing HER2 amplification in the primary tumor.

Conclusion

These results indicate that SISH can be a feasible alternative to FISH in the clinical setting. In node-positive breast cancer, confirmation of the HER2 status of the metastatic lymph nodes appears to be mandatory, regardless of the HER2 status of the primary tumors.

[HER-2 oncogene amplification assessment in invasive breast cancer by dual-color in situ hybridization (dc-CISH): a comparative study with fluorescent in situ hybridization (FISH)]

OBJECTIVES

The amplification of the gene encoding for the human epidermal growth factor receptor 2 (HER-2 oncogene), located on chromosome 17 (17q21-q22), or the overexpression of this receptor have prognostic and therapeutic implications in invasive breast cancer. An evaluation of the HER-2 status by immunohistochemistry (IHC) is performed on all invasive breast cancer cases. Fluorescent in situ hybridization (FISH) is considered as the gold standard for the detection of HER-2 gene amplification for IHC equivocal cases (score 2+). A more recent in situ hybridization technique, the dual-color chromogenic in situ hybridization (dc-CISH), has been proposed as an alternative to FISH. The aim of this study was to measure the correlation between dc-CISH and FISH for HER-2 oncogene amplification assessment in invasive breast cancer.

METHODS AND RESULTS

We built four tissue micro-array (TMA) blocs with 100 breast invasive cancer cases that had been previously tested by IHC for HER-2 detection: 10 score 0 cases, 10 score 3+cases, 39 score 1+and 41 score 2+cases. Both FISH and dc-CISH techniques were applied on all TMA cases as well as on two additional slides serving as controls. Interpretation of dc-CISH was carried out by a pathologist using an optical microscope. For FISH, the interpretation was done by a professional from the medical genetics department using a fluorescent microscope linked to a computer system for image capturing and analysis. The interpretation of the HER-2/CEN-17 ratio for both tests was in accordance with the values of the updated recommendations from the Canadian National Consensus Meeting on HER-2/neu testing in breast cancer and from the ASCO/CAP. Among the 100 cases initially included in the study, eight were excluded from the analysis due to sampling or technical flaws. From the 92 remaining cases, we obtained a concordance of 97.8% (90/92 cases) between the two techniques (Kappa coefficient 0.97, 95% confidence interval). The correlation coefficient (rho) between ratios was estimated at 0.57.

CONCLUSION

This study shows a strong concordance between FISH and dc-CISH techniques and indicates that dc-CISH is a good alternative method for HER-2 gene amplification assessment in breast cancer.

Molecular pathology of breast cancer: the journey from traditional practice toward embracing the complexity of a molecular classification

CONTEXT

Adenocarcinoma of the breast is the most frequent cancer affecting women in both developed and developing regions of the world. From the moment of clinical presentation until the time of pathologic diagnosis, patients affected by this disease will face daunting questions related to prognosis and treatment options. While improvements in targeted therapies have led to increased patient survival, these same advances have created the imperative to accurately stratify patients to achieve maximum therapeutic efficacy while minimizing side effects. In this evolving era of personalized medicine, there is an ever-increasing need to overcome the limitations of traditional diagnostic practice.

OBJECTIVE

To summarize the molecular diagnostics traditionally used to guide prognostication and treatment of breast carcinomas, to highlight published data on the molecular classification of these tumors, and to showcase molecular assays that will supplement traditional methods of categorizing the disease.

DATA SOURCES

A review of the literature covering the molecular diagnostics of breast carcinomas with a focus on the gene expression and array studies used to characterize the molecular signatures of the disease. Special emphasis is placed on summarizing evolving technologies useful in the diagnosis and characterization of breast carcinoma.

CONCLUSIONS

Available and emerging molecular resources will allow pathologists to provide superior diagnostic, prognostic, and predictive information about individual breast carcinomas. These advances should translate into earlier identification and tailored therapy and should ultimately improve outcome for patients affected by this disease.

Dual-color silver-enhanced in situ hybridization for assessing HER2 gene amplification in breast cancer

Amplification of the human epidermal growth factor receptor 2 (HER2) gene occurs in 20-25% of breast cancers, and is recognized as a prognostic and predictive marker. HER2 gene amplification, evaluated as a change in protein expression or gene copy number, can be identified by a number of methods. Fluorescence in situ hybridization (FISH) is considered the gold standard for HER2 gene copy number determination; however, a number of impediments prevent its wider use in a clinical setting. The aims of our study were to compare dual-color silver-enhanced in situ hybridization (SISH) with single-color SISH and FISH on formalin-fixed, paraffin-embedded sections, and to validate its use as a routine method for assessing HER2 status in breast cancers. A total of 146 invasive breast carcinoma cases were assessed for HER2 gene amplification by FISH and dual-color SISH. Dual-color SISH and FISH results exhibited a concordance rate of 97% (κ=0.912). A comparison of the single-color SISH method with dual-color SISH showed that 142 of 146 cases were in agreement (97%, κ=0.930). Our results showed that dual-color SISH is a viable alternative to FISH that offers a number of advantages in a clinical setting.

The immunohistochemistry laboratory: looking at molecules and preparing for tomorrow

CONTEXT

Surgical and subspecialty pathologists rely heavily on the patient's clinical context, imaging studies, morphology, and on ancillary studies such as immunohistochemistry (IHC), cytogenetics, and molecular diagnostics in arriving at accurate, contemporary diagnoses. Lymphoma/leukemia classification has led the way in the number of antibodies used in IHC algorithmic diagnostic approaches to distinguish more than 40 diseases. As the era of genomics, transcriptomics, proteomics, and targeted pathway therapeutics unfolds-and as infusion of federal funds to programs such as Accelerating Clinical Trials of Novel Oncologic PathWays (ACTNOW) requires that correlative biomarker assays be performed in Clinical Laboratory Improvement Amendments of 1988 (CLIA)-certified IHC laboratories-we face changes and challenges for the future.

OBJECTIVE

To discuss the laboratory, pertinent daily diagnostic, prognostic, and therapeutic uses of IHC, and future directions and challenges.

DATA SOURCES

Recent literature review and ongoing current activities in our laboratory and institution.

CONCLUSIONS

Meticulous attention at the microscope by expert subspecialty pathologists using ancillary methods is important in making correct diagnoses. Awareness of the literature and interactions with our research colleagues, including clinical, basic, and translational scientists, continue to expand our insights into and understanding of complex diseases; this will ultimately provide prognostic information to assist in appropriate clinical management of our patients and development of new targeted or combination therapies. Multimodality correlations will continue, with morphology, imaging data, immunophenotyping, and genetics as well as steadily increasing integration of pathway signaling, genome, sequenome, transcriptome, and proteome data used in clinical settings.

Receptor conversion in distant breast cancer metastases

INTRODUCTION

When breast cancer patients develop distant metastases, the choice of systemic treatment is usually based on tissue characteristics of the primary tumor as determined by immunohistochemistry (IHC) and/or molecular analysis. Several previous studies have shown that the immunophenotype of distant breast cancer metastases may be different from that of the primary tumor ("receptor conversion"), leading to inappropriate choice of systemic treatment. The studies published so far are however small and/or methodologically suboptimal. Therefore, definite conclusions that may change clinical practice could not yet be drawn. We therefore aimed to study receptor conversion for estrogen receptor alpha (ERα), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) in a large group of distant (non-bone) breast cancer metastases by re-staining all primary tumors and metastases with current optimal immunohistochemical and in situ hybridization methods on full sections.

METHODS

233 distant breast cancer metastases from different sites (76 skin, 63 liver, 43 lung, 44 brain and 7 gastro-intestinal) were IHC stained for ERα, PR and HER2, and expression was compared to that of the primary tumor. HER2 in situ hybridization (ISH) was done in cases of IHC conversion or when primary tumors or metastases showed an IHC 2+ result.

RESULTS

Using a 10% threshold, receptor conversion by IHC for ERα, PR occurred in 10.3%, 30.0% of patients, respectively. In 10.7% of patients, conversion from "ER+ or PR+" to ER-/PR- and in 3.4% from ER-/PR- to "ER+ or PR+" was found. Using a 1% threshold, ERα and PR conversion rates were 15.1% and 32.6%. In 12.4% of patients conversion from "ER+ or PR+" to ER-/PR-, and 8.2% from ER-/PR- to "ER+ or PR+" occurred. HER2 conversion occurred in 5.2%. Of the 12 cases that showed HER2 conversion by IHC, 5 showed also conversion by ISH. One further case showed conversion by ISH, but not by IHC. Conversion was mainly from positive in the primary tumor to negative in the metastases for ERα and PR, while HER2 conversion occurred equally both ways. PR conversion occurred significantly more often in liver, brain and gastro-intestinal metastases.

CONCLUSIONS

Receptor conversion by immunohistochemistry in (non-bone) distant breast cancer metastases does occur, is relatively uncommon for ERα and HER2, and more frequent for PR, especially in brain, liver and gastro-intestinal metastases.

Analysis of messenger RNA expression by in situ hybridization using RNA probes synthesized via in vitro transcription

The analysis of the spatial patterning of mRNA expression is critically important for assigning functional and physiological significance to a given gene product. Given the tens of thousands of mRNAs in the mammalian genome, a full assessment of individual gene functions would ideally be overlaid upon knowledge of the specific cell types expressing each mRNA. In situ hybridization approaches represent a molecular biological/histological method that can reveal cellular patterns of mRNA expression. Here, we present detailed procedures for the detection of specific mRNAs using radioactive RNA probes in tissue sections followed by autoradiographic detection. These methods allow for the specific and sensitive detection of spatial patterns of mRNA expression, thereby linking mRNA expression with cell type and function. Radioactive detection methods also facilitate semi-quantitative analyses of changes in mRNA gene expression.

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.

Emerging technologies for assessing HER2 amplification

Patients with human epidermal growth factor receptor-2 (HER2)+ breast cancer are eligible for trastuzumab treatment; therefore, accurate assessment of HER2 status is essential. Until recently, only 2 methods were validated for determining the HER2 status of breast tumors in the routine diagnostic setting: immunohistochemical analysis and fluorescence in situ hybridization (FISH). Recently, bright-field in situ hybridization techniques such as chromogenic in situ hybridization (CISH) and silver-enhanced in situ hybridization (SISH), which combine features of immunohistochemical analysis and FISH, have been introduced for the determination of HER2 status. These new techniques use a peroxidase enzyme-labeled probe with chromogenic detection, instead of a fluorescent-labeled probe, allowing results to be visualized by standard bright-field microscopy. Thus, the histologic features and HER2 status of a specimen can be evaluated in parallel. Moreover, signals do not decay over time. This review discusses recent publications regarding CISH and SISH testing, including results scoring and concordance between FISH and immunohistochemical analysis.

Development of automated brightfield double in situ hybridization (BDISH) application for HER2 gene and chromosome 17 centromere (CEN 17) for breast carcinomas and an assay performance comparison to manual dual color HER2 fluorescence in situ hybridization (FISH)

Background

Human epidermal growth factor receptor 2 (HER2) fluorescence in situ hybridization (FISH) is a quantitative assay for selecting breast cancer patients for trastuzumab therapy. However, current HER2 FISH procedures are labor intensive, manual methods that require skilled technologists and specialized fluorescence microscopy. Furthermore, FISH slides cannot be archived for long term storage and review. Our objective was to develop an automated brightfield double in situ hybridization (BDISH) application for HER2 gene and chromosome 17 centromere (CEN 17) and test the assay performance with dual color HER2 FISH evaluated breast carcinomas.

Methods

The BDISH assay was developed with the nick translated dinitrophenyl (DNP)-labeled HER2 DNA probe and DNP-labeled CEN 17 oligoprobe on the Ventana BenchMark^® XT slide processing system. Detection of HER2 and CEN 17 signals was accomplished with the silver acetate, hydroquinone, and H₂O₂ reaction with horseradish peroxidase (HRP) and the fast red and naphthol phosphate reaction with alkaline phosphatise (AP), respectively. The BDISH specificity was optimized with formalin-fixed, paraffin-embedded xenograft tumors, MCF7 (non-amplified HER2 gene) and BT-474 (amplified HER2 gene). Then, the BDISH performance was evaluated with 94 routinely processed breast cancer tissues. Interpretation of HER2 and CEN 17 BDISH slides was conducted by 4 observers using a conventional brightfield microscope without oil immersion objectives.

Results

Sequential hybridization and signal detection for HER2 and CEN 17 ISH demonstrated both DNA targets in the same cells. HER2 signals were visualized as discrete black metallic silver dots while CEN 17 signals were detected as slightly larger red dots. Our study demonstrated a high consensus concordance between HER2 FISH and BDISH results of clinical breast carcinoma cases based on the historical scoring method (98.9%, Simple Kappa = 0.9736, 95% CI = 0.9222 – 1.0000) and the ASCO/CAP scoring method with the FISH equivocal cases (95.7%, Simple Kappa = 0.8993%, 95% CI = 0.8068 – 0.9919) and without the FISH equivocal cases (100%, Simple Kappa = 1.0000%, 95% CI = 1.0000 – 1.0000).

Conclusion

Automated BDISH applications for HER2 and CEN 17 targets were successfully developed and it might be able to replace manual two-color HER2 FISH methods. The application also has the potential to be used for other gene targets. The use of BDISH technology allows the simultaneous analyses of two DNA targets within the context of tissue morphological observation.