HER2 immunohistochemical and fluorescence in situ hybridization discordances in invasive breast carcinoma with micropapillary features.

The 2013 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) recommendations for HER2 testing contain a recommendation for pathologists with respect to invasive micropapillary carcinoma. The guidelines suggest that HER2 immunohistochemical staining that is intense but incomplete and would be considered 1+ may actually be HER2-amplified by fluorescence in situ hybridization. Thus, pathologists should consider reporting the immunohistochemistry as equivocal (2+) and employ an alternative testing methodology. This recommendation is based largely on one paper wherein the authors tested a series of 22 micropapillary carcinomas that were considered 1+ by immunohistochemistry and identified HER2 amplification in one case (5%). In order to assess for a possible discordance between HER2 immunohistochemistry and fluorescence in situ hybridization, we evaluated a series of invasive carcinomas with micropapillary features using both methodologies. As described by the WHO, invasive carcinomas with micropapillary features have small, hollow, or morula-like clusters of cells surrounded by clear stromal spaces. All cases had HER2 immunohistochemistry and fluorescence in situ hybridization performed, and for cases with equivocal fluorescence in situ hybridization results, an alternative Chromosome 17 probe (RAI1) was employed. All assays were scored according to the 2013 ASCO/CAP guidelines. Specifically for this study, immunohistochemistry was scored irrespective of the presence of micropapillary features. Overall, we identified HER2 amplification in 21 (47%) of the cases assayed, with the corresponding immunohistochemistry being 1+ (n=9), 2+ (n=11), and 3+ (n=1). The ASCO/CAP recommendation that this morphology may deviate from the typical staining pattern is highlighted, as we found that 43% of cases with micropapillary features and HER2 staining that would otherwise be scored as 1+ were HER2-amplified by fluorescence in situ hybridization. This study supports the ASCO/CAP recommendation that pathologists should consider reporting immunohistochemistry in this morphology as equivocal and perform reflex testing using in situ hybridization.

Quantitative Imaging Analysis Fluorescence In Situ Hybridization Validation for Clinical HER2 Testing in Breast Cancer.

CONTEXT.­: Quantitative imaging is a promising tool that is gaining wide use across several areas of pathology. Although there has been increasing adoption of morphologic and immunohistochemical analysis, the adoption of evaluation of fluorescence in situ hybridization (FISH) on formalin-fixed, paraffin-embedded tissue has been limited because of complexity and lack of practice guidelines. OBJECTIVE.­: To perform human epidermal growth factor receptor 2 (HER2) FISH validation in breast carcinoma in accordance with the American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) 2018 guideline. DESIGN.­: Clinical validation of HER2 FISH was performed using the US Food and Drug Administration-approved dual-probe HER2 IQFISH (Dako, Carpinteria, California) with digital scanning performed on a PathFusion (Applied Spectral Imaging, Carlsbad, California) system. Validation parameters evaluated included z-stacking, classifier, accuracy, precision, software, and hardware settings. Finally, we evaluated the performance of digital enumeration on clinical samples in a real-world setting. RESULTS.­: The accuracy samples showed a final concordance of 95.3% to 100% across HER2 groups 1 to 5. During clinical implementation for HER2 groups 2, 3, and 4, we achieved a final concordance of 76% (95 of 125). Of these cases, only 8% (10 of 125) had discordances with clinical impact that could be identified algorithmically and triaged for manual review. CONCLUSIONS.­: Digital FISH enumeration is a useful tool to improve the efficacy of HER2 FISH enumeration and capture genetic heterogeneity across HER2 signals. Excluding cases with high background or poor image quality and manual review of cases with ASCO/CAP group discordances can further improve the efficiency of digital HER2 FISH enumeration.

Histopathological Correlation of Chromosome 12 Polysomy by Fluorescence in Situ Hybridization in Adipocytic Neoplasms.

Background: Identification of MDM2 amplification by fluorescence in situ hybridization is an important diagnostic tool for evaluation of adipocytic neoplasms. Rarely, neoplasms can show increased copies of MDM2 and CEP12 probes (polysomy) without amplification (MDM2/CEP12 ratio <2.0). While noted in the literature, this finding has not been the focus of any study to date. Methods: Consecutive cases were retrospectively screened for increased copies of MDM2 and CEP12 and were classified as: high polysomy (ratio<2.0, CEP12≥10.0), low polysomy (ratio<2.0, but >0.5, CEP12≥4.0 but <9.9), and CEP12 amplification (ratio≤0.5, CEP12 > 4.0). H&E slides were classified by a pathologist into diagnostic categories based on morphology without knowledge of MDM2 amplification result. Correlations between chromosome 12 polysomy and histological features in the same region of the tumor were investigated. Results: There were 19 (0.7%) high polysomy, 52 (2.0%) low polysomy and 3 (0.1%) CEP12 amplification cases identified in the 2541 cases screened. While low polysomy was seen across benign and malignant adipocytic tumors and other sarcomas, high level polysomy was primarily seen in liposarcomas, both atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDLPS) and dedifferentiated liposarcoma (DDLPS). No lipomas were high polysomy. Conclusion: Polysomy is an uncommon, but distinct, finding in adipocytic neoplasms found across the spectrum of benign to malignant with little insight into the pathophysiology or prognosis. While low polysomy is also observed in benign adipocytic neoplasms, high polysomy is almost always seen in malignant adipocytic neoplasms and is uncommon in benign adipocytic neoplasms.

Papillary intralymphatic angioendothelioma of the thigh: A case report and review of the literature.

The term angiosarcoma, encompasses several neoplasms, all of which exhibit a malignant process derived from endothelial cells of the vessels. The most common form of angiosarcoma is highly aggressive, often fatal, and usually affects the head and neck region of elderly white men. Other low-grade forms of angiosarcoma, including papillary intralymphatic angioendothelioma, also known as Dabska tumor, are less invasive, affect a wider age range, and offer a better prognosis. There are several predisposing factors that increase the risk of angiosarcoma and include chronic lymphedema of the extremities, preexisting vascular lesions, and prior radiation, often as therapy for other malignancies. We report an unusual case of a very small, low-grade angiosarcoma on the thigh of an adult female with no known predisposing risk factors.

The FDA-Approved Breast Cancer HER2 Evaluation Kit (HercepTest; Dako) May Miss Some HER2-Positive Breast Cancers.

OBJECTIVES: Accurate evaluation of human epidermal growth factor receptor 2 (HER2) in breast cancer is critical. METHODS: HER2 fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) tests were performed on 52 cases using a US Food and Drug Administration (FDA)-approved kit (HercepTest, FDA kit) and a laboratory-developed test (LDT) with the HercepTest antibody and a Leica Bond automated stainer. RESULTS: By FISH, 22 were HER2 positive, 29 were negative, and one was equivocal. Of the 22 HER2 FISH-positive cases, five were negative by the FDA kit and none by LDT. The five discrepant cases were retested using the same FDA kit in another Clinical Laboratory Improvement Amendments-certified laboratory, and all five cases were still negative. None of the 29 HER2 FISH-negative cases were positive by the FDA kit or LDT. The overall IHC-FISH concordance rate was 90.4% for the FDA kit and 100% for the LDT. CONCLUSIONS: The FDA kit may miss some HER2-positive cases. The LDT has a higher sensitivity and a higher concordance rate with FISH results.