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

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.

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.

Investigation of the origin of stromal and endothelial cells at the desmoplastic interface in xenograft tumor in mice

Carcinoma-associated fibroblasts found at the interface between a tumor and the normal stroma play several roles in the development of cancer, including cancer initiation, growth, and progression, thereby also affecting patient prognosis. Although recent studies have focused on carcinoma-associated fibroblasts as potential treatment targets, the origin of these fibroblasts remains unclear. One theory suggests that these cells arise from tumor cells undergoing the epithelial-mesenchymal transition, i.e., tumor cells transform into carcinoma-associated fibroblasts. Therefore, in this study, we aimed to elucidate the cellular origin of carcinoma-associated fibroblasts in a mouse xenograft model. Mice were transplanted with human lung cancer cells (H226 and A549 cells). After sacrifice, tumor masses and surrounding tissues were excised. Interestingly, the excised xenograft tissues contained a significant proportion of desmoplastic fibroblasts that exhibited strong expression of α-smooth muscle actin (SMA). Immunohistochemical staining with pan-cytokeratin, vimentin, β-catenin, E-cadherin, and CD34 showed no evidence of the epithelial-mesenchymal transition. Additional evaluation using dual-color silver in situ hybridization with dinitrophenyl-labeled human epidermal growth factor receptor 2 (HER2) and digoxigenin-labeled chromosome 17 centromere probes also showed similar results. In conclusion, our results revealed that the epithelial-mesenchymal transition may not occur in tumor xenograft models, regardless of evidence supporting this phenomenon in humans.

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.

Concomitant detection of HER2 protein and gene alterations by immunohistochemistry (IHC) and silver enhanced in situ hybridization (SISH) identifies HER2 positive breast cancer with and without gene amplification

Introduction

HER2 status assessment became a mandatory test assay in breast cancer, giving prognostic and predictive information including eligibility for adjuvant anti-HER2 therapy. Precise and reliable assessment of HER2 status is therefore of utmost importance. In this study we analyzed breast cancer samples by a novel technology for concomitant detection of the HER2 protein and gene copy number.

Methods

Tissue microarrays containing 589 invasive breast cancer samples were analyzed with a double immunohistochemistry (IHC) and silver labeled in situ hybridization (SISH) assay simultaneously detecting HER2 protein and gene copy number in the same tumor cells. This bright-field assay was analyzed using scores according to the modified ASCO guidelines and the results were correlated with patient prognosis.

Results

Overall concordance rate between protein expression and the presence of gene amplification was 98%. Fifty-seven of 60 tumors (95%) with IHC score 3+, 6 of 10 tumors with IHC score 2+ (60%) and only 3 of 519 tumors (0.6%) with IHC score 0/1+ were amplified by SISH. Patients with gene amplification despite IHC score 0/1+ had a tendency for worse overall survival (p = 0.088, reaching nearly statistical significance) compared to IHC score 0/1+ without amplification. In contrast, there was no difference in overall survival in IHC score 3+/2+ tumors with and without gene amplification.

Conclusions

The novel double IHC and SISH assay for HER2 is efficient in the identification of breast cancer with discordant HER2 protein and HER2 gene status, especially for the prognostically relevant groups of HER2 protein negative tumors with HER2 amplification and HER2 protein positive tumors without HER2 amplification. Breast cancer without HER2 amplification among IHC score 2+/3+ tumors (10% in our cohort) suggests that other mechanisms than gene amplification contribute to protein overexpression in these cells.

Determination of HER2 gene amplification in breast cancer using dual-color silver enhanced in situ hybridization (dc- SISH) and comparison with fluorescence ISH (FISH)

BACKGROUND

The two basic methods that are currently accepted to identify the HER2 status are immunohistochemistry and flyorescence in situ hybridization (FISH) . The aim of this study was to perform the dual-color silver in situ hybridization (dc-SISH) technique as an alternative to FISH.

MATERIALS AND METHODS

A total of 40 invasive breast carcinoma cases were assessed for HER2 gene amplification by FISH and dual- color SISH.

RESULTS

Significant correlation was found in the HER2 expression results obtained with the two approaches (p=0.001, p<0.05). The concordance rate was 92.3%.

CONCLUSIONS

Foutine practical use of the dc-SISH method, which is much easier to apply, score, and evaluate, has many advantages. HER2 and CEN17 status can be evaluated simultaneously with the newly developed "Dual-Color Probe". All these specifications and the reliable results obtained support the widespread use of SISH technique in clinical practice.