HER2 in situ hybridization in breast cancer: clinical implications of polysomy 17 and genetic heterogeneity

Navigating HER2-Low Testing in Invasive Breast Cancer: Update Recommendations for Pathologists

The article discusses the importance of accurately distinguishing HER2-low from HER2-negative breast cancer, as novel ADCs have demonstrated activity in a large population of patients with HER2-low-expressing BC. While current guidelines recommend a dichotomous classification of HER2 as either positive or negative, the emergence of the HER2-low concept calls for standardization of HER2 testing in breast cancer, using currently available assays to better discriminate HER2 levels. This review covers the evolution and latest updates of the ASCO/CAP guidelines relevant to this important biomarker in breast cancer, including still-evolving concepts such as HER2 low, HER2 heterogeneity, and HER2 evolution. Our group presents the latest Mexican recommendations for HER2 status evaluation in breast cancer, considering the ASCO/CAP guidelines and introducing the HER2-low concept. In the era of personalized medicine, accurate HER2 status assessment remains one of the most important biomarkers in breast cancer, and the commitment of Mexican pathologists to theragnostic biomarker quality is crucial for providing the most efficient care in oncology.

Utility of human epidermal growth factor 2 heterogeneity as a prognostic factor in triple-negative breast cancer

In some cases of human epidermal growth factor 2 (HER2)-negative breast cancer, including triple-negative breast cancer, HER2 expression is sporadically and strongly upregulated, a condition known as HER2 heterogeneity. We investigated the clinicopathological features of patients with HER2 heterogeneity in triple-negative breast cancers treated with neoadjuvant chemotherapy. Thirty-nine patients with triple-negative breast cancer who had undergone preoperative chemotherapy participated in this study. To assess for HER2 heterogeneity, we used dual in situ hybridization slides. We evaluated the association between HER2 heterogeneity and clinicopathological factors such as rates of pathologic complete response (pCR) and of recurrence-free survival. Of the 39 patients, 15 (38.5%) had cancers with HER2 heterogeneity. The pCR rates were 13.3% among patients with HER2 heterogeneity and 20.8% among those with HER2 nonheterogeneity, but the difference was not significant. The recurrence-free survival rate was significantly lower in patients with HER2 heterogeneity than in those without (P = 0.025). HER2 heterogeneity is a significant predictor of poor prognosis in patients with triple-negative breast cancer treated with neoadjuvant chemotherapy.

High HER2 Intratumoral Heterogeneity Is a Predictive Factor for Poor Prognosis in Early-Stage and Locally Advanced HER2-Positive Breast Cancer

PURPOSE

Breast cancer tumors frequently have intratumoral heterogeneity (ITH). Tumors with high ITH cause therapeutic resistance and have human epidermal growth factor receptor 2 (HER2) heterogeneity in response to HER2-targeted therapies. This study aimed to investigate whether high HER2 heterogeneity levels were clinically related to a poor prognosis for HER2-targeted adjuvant therapy resistance in primary breast cancers.

METHODS

This study included patients with primary breast cancer (n = 251) treated with adjuvant HER2-targeted therapies. HER2 heterogeneity was manifested by the shape of HER2 fluorescence in situ hybridization amplification (FISH) distributed histograms with the HER2 gene copy number within a tumor sample. Each tumor was classified into a biphasic grade graph (high heterogeneity [HH]) group or a monophasic grade graph (low heterogeneity [LH]) group based on heterogeneity. Both groups were evaluated for disease-free survival (DFS) and overall survival (OS) for a median of ten years of annual follow-up.

RESULTS

Of 251 patients with HER2-positive breast cancer, 46 (18.3%) and 205 (81.7%) were classified into the HH and LH groups, respectively. The HH group had more distant metastases and a poorer prognosis than the LH group (DFS: p < 0.001 (HH:63% vs. LH:91% at 10 years) and for the OS: p = 0.012 (HH:78% vs. LH:95% at 10 years).

CONCLUSIONS

High HER2 heterogeneity is a poor prognostic factor in patients with HER2-positive breast cancer. A novel approach to heterogeneity, which is manifested by the shape of HER2 FISH distributions, might be clinically useful in the prognosis prediction of patients after HER2 adjuvant therapy.

Atypical Co-amplification with Co-localization of HER2 Gene in Breast Cancer: Combined IHC/FISH Approach as per ASCO/CAP 2018 Guidelines for Targeted Therapy Eligibility

Breast cancer patients with HER2 gene amplification as assessed by FISH are eligible for HER2-targeted therapy. However, in a small subset of patients, unusual FISH pattern of co-localization and co-amplification can pose challenges in interpretation of the HER2 status and hence to assess the HER2 status accurately; our aim was to report their incidence and analyze them based on latest ASCO/CAP 2018 guidelines. We present seven cases with HER2/CEP17 co-amplification and co-localization from a total 4040 cases referred during the year 2017 to 2021 at Mumbai Reference Laboratory, SRL Diagnostics. Core needle biopsy/excision invasive breast carcinoma specimens from metastatic sites were tested for IHC for expressions of ER, PR, and HER2. The ones which came equivocal on HER2 IHC were then evaluated for HER2 amplification by FISH. Co-amplification and co-localization of HER2 and centromeric 17 was observed with a frequency of 0.1% that falls in the range of 0.5-0.1% as reported from other large-scale studies. Our study showed that implementation of a binary inhouse concurrent assessment with IHC as per the ASCO/CAP 2018 helps to reach the most definitive and accurate HER2 status. Our study is an attempt to report such challenging FISH patterns and their work-up for a better understanding on the interpretation. Cumulative data along with follow-up in these cases would bring an insight into exact therapeutic outcome.

Management of patients with advanced-stage HER2-positive breast cancer: current evidence and future perspectives

Amplification and/or overexpression of ERBB2, the gene encoding HER2, can be found in 15-20% of invasive breast cancers and is associated with an aggressive phenotype and poor clinical outcomes. Relentless research efforts in molecular biology and drug development have led to the implementation of several HER2-targeted therapies, including monoclonal antibodies, tyrosine-kinase inhibitors and antibody-drug conjugates, constituting one of the best examples of bench-to-bedside translation in oncology. Each individual drug class has improved patient outcomes and, importantly, the combinatorial and sequential use of different HER2-targeted therapies has increased cure rates in the early stage disease setting and substantially prolonged survival for patients with advanced-stage disease. In this Review, we describe key steps in the development of the modern paradigm for the treatment of HER2-positive advanced-stage breast cancer, including selecting and sequencing new-generation HER2-targeted therapies, and summarize efficacy and safety outcomes from pivotal studies. We then outline the factors that are currently known to be related to resistance to HER2-targeted therapies, such as HER2 intratumoural heterogeneity, activation of alternative signalling pathways and immune escape mechanisms, as well as potential strategies that might be used in the future to overcome this resistance and further improve patient outcomes.

Clinical application of the HM-1000 image processing for HER2 fluorescence in situ hybridization signal quantification in breast cancer

BACKGROUND

Accurate quantification of human epidermal growth factor receptor 2 (HER2) gene amplification is important for predicting treatment response and prognosis in patients with breast cancer. Fluorescence in situ hybridization (FISH) is the gold standard for the diagnosis of HER2 status, particularly in cases with equivocal status on immunohistochemistry (IHC) staining, but has some limitations of non-classical amplifications and such cases are diagnosed basing on additional IHC and FISH. This study investigated the clinical utility of a novel super-resolution fluorescence microscopy technique for the better FISH signal visualization and HER2 FISH classification.

METHODS

Fourteen breast cancer tissue samples were retrospectively collected between September 2018 and February 2022, and FISH HER2 signal quantification was evaluated by determining the HER2/chromosome 17 centromere (CEP17) ratio and the number of HER2 signals per nucleus in super- versus conventional-resolution images.

RESULTS

Super-resolution images maintained the same overall HER2 diagnosis from routine, but HER2 FISH amplification changed negative to monosomy in two cases. Two Letrozole non-response relapses coincided to monosomy samples. The median number of HER2 signals per nucleus was 7.5 in super-resolution images and 4.0 in conventional-resolution images in HER2-positive samples and 2.8 and 2.1 signals per nucleus, respectively, in HER2-negative samples.

CONCLUSIONS

Super-resolution images improved signal visualization, including a significant difference in the number of countable HER2 and CEP17 signals in a single nucleus compared with conventional-resolution images. Increased accuracy of signal quantification by super-resolution microscopy may provide clinicians with more detailed information regarding HER2 FISH status that allows to better FISH classification such as HER2-low samples.

HER2-targeted therapies in cancer: a systematic review

Abnormal alterations in human epidermal growth factor receptor 2 (HER2, neu, and erbB2) are associated with the development of many tumors. It is currently a crucial treatment for multiple cancers. Advanced in molecular biology and further exploration of the HER2-mediated pathway have promoted the development of medicine design and combination drug regimens. An increasing number of HER2-targeted drugs including specific monoclonal antibodies, tyrosine kinase inhibitors (TKIs), and antibody-drug conjugates (ADCs) have been approved by the U.S. Food and Drug Administration. The emergence of ADCs, has significantly transformed the treatment landscape for various tumors, such as breast, gastric, and bladder cancer. Classic monoclonal antibodies and novel TKIs have not only demonstrated remarkable efficacy, but also expanded their indications, with ADCs in particular exhibiting profound clinical applications. Moreover the concept of low HER2 expression signifies a breakthrough in HER2-targeted therapy, indicating that an increasing number of tumors and patients will benefit from this approach. This article, provides a comprehensive review of the underlying mechanism of action, representative drugs, corresponding clinical trials, recent advancements, and future research directions pertaining to HER2-targeted therapy.

Targeting HER2 heterogeneity in breast and gastrointestinal cancers

About 20% of breast and gastric cancers and 3% of colorectal carcinomas overexpress the human epidermal growth factor receptor 2 (HER2) and are sensitive to HER2-directed agents. The expression of HER2 may differ within the same tumoral lesion (spatial intralesional heterogeneity), from different tumor locations (spatial interlesional heterogeneity), and throughout treatments (temporal heterogeneity). Spatial and temporal heterogeneity may impact on response and resistance to HER2-targeting agents and its prevalence and predictive role changes across HER2-overexpressing solid tumors. Therefore, the definition and the characterization of HER2 heterogeneity pose many challenges and its implementation as a reproducible predictive biomarker would help in guiding treatment modulation.

Emerging Landscape of Targeted Therapy of Breast Cancers With Low Human Epidermal Growth Factor Receptor 2 Protein Expression

CONTEXT.—

Human epidermal growth factor receptor 2 (HER2) status in breast cancer is currently classified as negative or positive for selecting patients for anti-HER2 targeted therapy. The evolution of the HER2 status has included a new HER2-low category defined as an HER2 immunohistochemistry score of 1+ or 2+ without gene amplification. This new category opens the door to a targetable HER2-low breast cancer population for which new treatments may be effective.

OBJECTIVE.—

To review the current literature on the emerging category of breast cancers with low HER2 protein expression, including the clinical, histopathologic, and molecular features, and outline the clinical trials and best practice recommendations for identifying HER2-low-expressing breast cancers by immunohistochemistry.

DATA SOURCES.—

We conducted a literature review based on peer-reviewed original articles, review articles, regulatory communications, ongoing and past clinical trials identified through ClinicalTrials.gov, and the authors' practice experience.

CONCLUSIONS.—

The availability of new targeted therapy potentially effective for patients with breast cancers with low HER2 protein expression requires multidisciplinary recognition. In particular, pathologists need to recognize and identify this category to allow the optimal selection of patients for targeted therapy.

Qualification of a multiplexed tissue imaging assay and detection of novel patterns of HER2 heterogeneity in breast cancer

Emerging data suggests that HER2 intratumoral heterogeneity (ITH) is associated with therapy resistance, highlighting the need for new strategies to assess HER2 ITH. A promising approach is leveraging multiplexed tissue analysis techniques such as cyclic immunofluorescence (CyCIF), which enable visualization and quantification of 10-60 antigens at single-cell resolution from individual tissue sections. In this study, we qualified a breast cancer-specific antibody panel, including HER2, ER, and PR, for multiplexed tissue imaging. We then compared the performance of these antibodies against established clinical standards using pixel-, cell- and tissue-level analyses, utilizing 866 tissue cores (representing 294 patients). To ensure reliability, the CyCIF antibodies were qualified against HER2 immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) data from the same samples. Our findings demonstrate the successful qualification of a breast cancer antibody panel for CyCIF, showing high concordance with established clinical antibodies. Subsequently, we employed the qualified antibodies, along with antibodies for CD45, CD68, PD-L1, p53, Ki67, pRB, and AR, to characterize 567 HER2+ invasive breast cancer samples from 189 patients. Through single-cell analysis, we identified four distinct cell clusters within HER2+ breast cancer exhibiting heterogeneous HER2 expression. Furthermore, these clusters displayed variations in ER, PR, p53, AR, and PD-L1 expression. To quantify the extent of heterogeneity, we calculated heterogeneity scores based on the diversity among these clusters. Our analysis revealed expression patterns that are relevant to breast cancer biology, with correlations to HER2 ITH and potential relevance to clinical outcomes.

Complementary Tumor Diagnosis by Single Cell-Based Cytogenetics Using Multi-marker Fluorescence In Situ Hybridization (mFISH)

Multi-color (or multi-marker) fluorescence in situ hybridization (mFISH) is a well-established, valuable, complementary tool for prenatal and pathological (tumor) diagnosis. A variety of chromosomal abnormalities, such as partial or total chromosomal gains, losses, inversions, or translocations, which are considered to cause genetic syndromes, can relatively easily be detected on a cell-by-cell basis. Individual cells either in suspension (e.g., in the form of a cytological specimen derived from body fluids) or within a tissue (e.g., a solid tumor specimen or biopsy) can be quantitatively evaluated with respect to the chromosomal hybridization markers of interest (e.g., a gene or centromeric region) and with due consideration of cellular heterogeneity. FISH is helpful or even essential for the (sub-)classification, stratification, and unambiguous diagnosis of a number of malignant diseases and contributes to treatment decision in many cases. Here, the diagnostic power and limitations of typical FISH and mFISH approaches (except chromosome painting and RNA hybridization) are discussed, with special emphasis on tumor and single-cell diagnostics. Well-established and novel FISH protocols, the latter addressed to accelerate and flexibilize the preparation and hybridization of formalin-fixed and paraffin-embedded tissues, are provided. Moreover, guidelines and molecular aspects important for data interpretation are discussed. Finally, sophisticated multiplexed approaches and those that analyze very rare single-cell events, which are not yet implemented in diagnostic procedures, will be touched upon. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: (m)FISH applied to formaldehyde-fixed paraffin-embedded tissues Basic Protocol 2: (m)FISH applied to cytological specimens.

Improved concordance of challenging human epidermal growth factor receptor 2 dual in-situ hybridisation cases with the use of a digital image analysis algorithm in breast cancer

AIMS

Accurate assessment of human epidermal growth factor receptor 2 (HER2) expression by HER2 immunohistochemistry and in-situ hybridisation (ISH) is critical for the management of patients with breast cancer. The revised 2018 ASCO/CAP guidelines define 5 groups based on HER2 expression and copy number. Manual pathologist quantification by light microscopy of equivocal and less common HER2 ISH groups (groups 2-4) can be challenging, and there are no data on interobserver variability in reporting of these cases. We sought to determine whether a digital algorithm could improve interobserver variability in the assessment of difficult HER2 ISH cases.

METHODS AND RESULTS

HER2 ISH was evaluated in a cohort enriched for less common HER2 patterns using standard light microscopy versus analysis of whole slide images using the Roche uPath HER2 dual ISH image analysis algorithm. Standard microscopy demonstrated significant interobserver variability with a Fleiss's kappa value of 0.471 (fair-moderate agreement) improving to 0.666 (moderate-good) with the use of the algorithm. For HER2 group designation (groups 1-5), there was poor-moderate reliability between pathologists by microscopy [intraclass correlation coefficient (ICC) = 0.526], improving to moderate-good agreement (ICC = 0.763) with the use of the algorithm. In subgroup analysis, the algorithm improved concordance particularly in groups 2, 4 and 5. Time to enumerate cases was also significantly reduced.

CONCLUSION

This work demonstrates the potential of a digital image analysis algorithm to improve the concordance of pathologist HER2 amplification status reporting in less common HER2 groups. This has the potential to improve therapy selection and outcomes for patients with HER2-low and borderline HER2-amplified breast cancers.

Deep learning to automatically evaluate HER2 gene amplification status from fluorescence in situ hybridization images

Human epidermal growth factor receptor 2 (HER2) gene amplification helps identify breast cancer patients who may respond to targeted anti-HER2 therapy. This study aims to develop an automated method for quantifying HER2 fluorescence in situ hybridization (FISH) signals and improve the working efficiency of pathologists. An Aitrox artificial intelligence (AI) model based on deep learning was constructed, and a comparison between the AI model and traditional manual counting was performed. In total, 918 FISH images from 320 consecutive invasive breast cancers were analysed and automatically classified into 5 groups according to the 2018 ASCO/CAP guidelines. The overall classification accuracy was 85.33% (157/184) with a mean average precision of 0.735. In Group 5, the most common group, the consistency was as high as 95.90% (117/122), while the consistency was low in the other groups due to the limited number of cases. The causes of this inconsistency, including clustered HER2 signals, coarse CEP17 signals and some section quality problems, were analysed. The developed AI model is a reliable tool for evaluating HER2 amplification statuses, especially for breast cancer in Group 5; additional cases from multiple centres could further improve the accuracy achieved for other groups.

Multiomics technologies for comprehensive tumor microenvironment analysis in triple-negative breast cancer under neoadjuvant chemotherapy

Triple-negative breast cancer (TNBC) is one of the most aggressive breast cancer subtypes and is characterized by abundant infiltrating immune cells within the microenvironment. As standard care, chemotherapy remains the fundamental neoadjuvant treatment in TNBC, and there is increasing evidence that supplementation with immune checkpoint inhibitors may potentiate the therapeutic efficiency of neoadjuvant chemotherapy (NAC). However, 20-60% of TNBC patients still have residual tumor burden after NAC and require additional chemotherapy; therefore, it is critical to understand the dynamic change in the tumor microenvironment (TME) during treatment to help improve the rate of complete pathological response and long-term prognosis. Traditional methods, including immunohistochemistry, bulk tumor sequencing, and flow cytometry, have been applied to elucidate the TME of breast cancer, but the low resolution and throughput may overlook key information. With the development of diverse high-throughput technologies, recent reports have provided new insights into TME alterations during NAC in four fields, including tissue imaging, cytometry, next-generation sequencing, and spatial omics. In this review, we discuss the traditional methods and the latest advances in high-throughput techniques to decipher the TME of TNBC and the prospect of translating these techniques to clinical practice.

History and Future of HER2-Targeted Therapy for Advanced Gastric Cancer

Human epidermal growth factor receptor 2 (HER2) is a receptor tyrosine kinase that belongs to the human epidermal growth factor receptor family. It is overexpressed/amplified in approximately 20% of gastric or gastroesophageal junction cancers. HER2 is being developed as a therapeutic target in a variety of cancers, and several agents have been shown to be effective in breast cancer. The development of HER2-targeted therapy for gastric cancer successfully began with trastuzumab. However, while effective in breast cancer, the successive anti-HER2 agents lapatinib, T-DM1, and pertuzumab failed to demonstrate benefits regarding survival in gastric cancer compared with the existing standard therapies. Intrinsic differences lie between gastric and breast cancer in terms of HER2-positive tumor biology, which may make development difficult. Recently, a novel anti-HER2 agent, trastuzumab deruxtecan, was introduced, and the development of HER2-positive gastric cancer agents has been moving to the next stage. This review summarizes the current HER2-targeted therapy for gastric or gastroesophageal cancer in chronological order and describes the promising future of HER2-targeted therapy.

HER2 Intratumoral Heterogeneity in Breast Cancer, an Evolving Concept

Amplification and/or overexpression of human epidermal growth factor receptor 2 (HER2) in breast cancer is associated with an adverse prognosis. The introduction of anti-HER2 targeted therapy has dramatically improved the clinical outcomes of patients with HER2-positive breast cancer. Unfortunately, a significant number of patients eventually relapse and develop distant metastasis. HER2 intratumoral heterogeneity (ITH) has been reported to be associated with poor prognosis in patients with anti-HER2 targeted therapies and was proposed to be a potential mechanism for anti-HER2 resistance. In this review, we described the current definition, common types of HER2 ITH in breast cancer, the challenge in interpretation of HER2 status in cases showing ITH and the clinical applications of anti-HER2 agents in breast cancer showing heterogeneous HER2 expression. Digital image analysis has emerged as an objective and reproducible scoring method and its role in the assessment of HER2 status with ITH remains to be demonstrated.

HER2 Low Breast Cancer: A New Subtype or a Trojan for Cytotoxic Drug Delivery?

Despite the great progress made in the understanding of the biological behavior of certain types of invasive breast cancer, there is still no single histological or molecular classification that encompasses such diversity and accurately predicts the clinical course of distinct breast cancer subtypes. The long-lasting classification of breast cancer as HER2-positive vs. HER2-negative has recently come into question with the discovery of new antibody drug conjugates (ADC), which are proven to be remarkably efficient in treating HER2-low breast cancer. The HER2-low paradigm has challenged the traditional understanding of HER2 overexpression and emphasized the need for more robust HER2 testing in order to encompass HER2 intratumoral heterogeneity and spatial distribution more accurately. It is yet to be seen if low HER2 will remain merely a marker of HER2-equipped tumors targetable with ADCs or if distinctive molecular and phenotypic groups within HER2-low tumors will eventually be discerned.

Anticipating changes in the HER2 status of breast tumours with disease progression-towards better treatment decisions in the new era of HER2-low breast cancers

BACKGROUND

HER2 expression is often negative or low in primary breast cancers (BCs) but its changes with disease progression remain poorly known. We aimed to estimate them between primary and recurrent tumours, and identify predictive factors.

METHODS

We compared the HER2 status, and clinical and pathological characteristics by its evolution category (stable or changed), between all primary BCs and matched recurrences registered in our database in 2000-2020 (n = 512).

RESULTS

HER2-low tumours were the most prevalent at diagnosis (44.9%), followed by HER2-negative tumours (39.3%). HER2 status significantly changed in 37.3% of recurrences, mainly of HER2-negative and HER2-low tumours. HER2-negative tumours which relapsed as HER2-low significantly more frequently expressed oestrogen receptors (ER) and recurred later than stably HER2-negative tumours. Changed HER2 status in distant metastases correlated with lower proliferation rates and higher ER expression in primary tumours, and among metastases of hormone receptor-positive (HR+) tumours-with weak progesterone receptor (PR) expression in primary tumours.

CONCLUSIONS

HER2 status changes with BC progression, with enrichment of HER2-low tumours in advanced stages. The ER+/PR- status, low proliferation index and time to late recurrence correlated with these changes. These findings highlight the need of retesting recurrences, especially of HR + primary tumours, to identify candidates for new anti-HER2 therapies.

Impacts of HER2 immunohistochemical scores on response and outcomes of HER2-positive breast cancers after neoadjuvant therapy

BACKGROUND

Neoadjuvant systemic therapy (NST) is conducted in increased number of patients with breast cancer overexpressing human epidermal growth factor receptor 2 (HER2). Whether the intensity of HER2 protein expression determines response to treatment is challenged. This study aims to analyze the impact of HER2 immunohistochemical (IHC) scores on NST response and survival outcome.

METHODS

We analyzed a total of 197 patients with HER2-positive breast cancer receiving NST and definite surgery from a prospectively collected database. The analyzed endpoints included pathological complete response (pCR), disease-free survival (DFS), and overall survival (OS). More patients with IHC 2+/ in situ hybridization (ISH)-positive tumors presented positive for hormonal receptors, compared with those with IHC 3+ tumors. No clinicopathological features except tumor necrosis were significantly associated with pCR.

RESULTS

Both positive hormone receptors and IHC scores stood on the borderline in statistical analysis. IHC 3+ group tends to present a higher pCR rate than IHC 2+/ISH+ groups (52.5% vs. 34.3%). Patients who achieved pCR had better survival outcome than that of non-pCR group. The impact of pCR on survival reached the statistical significance in the IHC 3+ group both in DFS (90.9% vs. 76.5%; p = 0.004) and OS (97.4% vs. 83.2%; p = 0.002). Multivariate analysis demonstrated IHC scores as an independent predictor of survival outcome with the adjustment of tumor staging and pCR.

CONCLUSION

HER2 IHC score is an independent predictor for outcome. IHC 3+ tumors presented a trend of higher pCR rate and better outcome in HER2-positive breast cancer patients who receive NST.

UK recommendations for HER2 assessment in breast cancer: an update

The last UK breast cancer (BC) human epidermal growth factor receptor 2 (HER2) testing guideline recommendations were published in 2015. Since then, new data and therapeutic strategies have emerged. The American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) published a focused update in 2018 that reclassified in situ hybridisation (ISH) Group 2 (immunohistochemistry (IHC) score 2+and HER2/chromosome enumeration probe 17 (CEP17) ratio ≥2.0 and HER2 copy number <4.0 signals/cell), as well as addressed other concerns raised by previous guidelines. The present article further refines UK guidelines, with specific attention to definitions of HER2 status focusing on eight key areas: (1) HER2 equivocal (IHC 2+) and assignment of the ASCO/CAP ISH group 2 tumours; (2) the definition of the group of BCs with low IHC scores for HER2 with emphasis on the distinction between IHC score 1+ (HER2-Low) from HER2 IHC score 0 (HER2 negative); (3) reporting cases showing HER2 heterogeneity; (4) HER2 testing in specific settings, including on cytological material; (5) repeat HER2 testing, (6) HER2 testing turnaround time targets; (7) the potential role of next generation sequencing and other diagnostic molecular assays for routine testing of HER2 status in BC and (8) use of image analysis to score HER2 IHC. The two tiered system of HER2 assessment remains unchanged, with first line IHC and then ISH limited to IHC equivocal cases (IHC score 2+) but emerging data on the relationship between IHC scores and levels of response to anti-HER2 therapy are considered. Here, we present the latest UK recommendations for HER2 status evaluation in BC, and where relevant, the differences from other published guidelines.

Evaluation of ERBB2 mRNA Expression in HER2-Equivocal (2+) Immunohistochemistry Cases

Xpert Breast Cancer STRAT4 is a RT-qPCR platform that studies the mRNA expression of ESR1, PGR, MKI67 and ERBB2, providing a positive or negative result for each of these breast cancer biomarkers. Its concordance with immunohistochemistry (IHC) and in situ hybridization (ISH) has been previously demonstrated, but none of the previous works was focused on HER2-equivocal (2+) cases identified by IHC. Thus, we studied the concordance between IHC/ISH and STRAT4 results for 112 HER2 2+ IBC samples, using 148 HER2 0+, 1+ and 3+ (no-HER2 2+) samples for comparison. We found 91.3% accuracy for the determination of HER2 status globally, 99.3% for no-HER2 2+ samples and 80.7% for HER2 2+ samples. Regarding the other biomarkers, we obtained 96.4% accuracy for estrogen receptor, 84.1% for progesterone receptor and 58.2% for Ki67. Our results suggest that the use of ERBB2 mRNA for the evaluation of HER2 2+ cases is not a reliable reflex method to assess the ERBB2 amplification status.

Multimodality Imaging Review of HER2-positive Breast Cancer and Response to Neoadjuvant Chemotherapy

Human epidermal growth factor receptor 2 (HER2/neu or ErbB2)-positive breast cancers comprise 15%-20% of all breast cancers. The most common manifestation of HER2-positive breast cancer at mammography or US is an irregular mass with spiculated margins that often contains calcifications; at MRI, HER2-positive breast cancer may appear as a mass or as nonmass enhancement. HER2-positive breast cancers are often of intermediate to high nuclear grade at histopathologic analysis, with increased risk of local recurrence and metastases and poorer overall prognosis. However, treatment with targeted monoclonal antibody therapies such as trastuzumab and pertuzumab provides better local-regional control and leads to improved survival outcome. With neoadjuvant treatments, including monoclonal antibodies, taxanes, and anthracyclines, women are now potentially able to undergo breast conservation therapy and sentinel lymph node biopsy versus mastectomy and axillary lymph node dissection. Thus, the radiologist's role in assessing the extent of local-regional disease and response to neoadjuvant treatment at imaging is important to inform surgical planning and adjuvant treatment. However, assessment of treatment response remains difficult, with the potential for different imaging modalities to result in underestimation or overestimation of disease to varying degrees when compared with surgical pathologic analysis. In particular, the presence of calcifications at mammography is especially difficult to correlate with the results of pathologic analysis after chemotherapy. Breast MRI findings remain the best predictor of pathologic response. The authors review the initial manifestations of HER2-positive tumors, the varied responses to neoadjuvant chemotherapy, and the challenges in assessing residual cancer burden through a multimodality imaging review with pathologic correlation. ^© RSNA, 2023 Quiz questions for this article are available through the Online Learning Center.

Novel markers in breast pathology

Breast pathology is an ever-expanding database of information which includes markers, or biomarkers, that detect or help treat the disease as prognostic or predictive information. This review focuses on these aspects of biomarkers which are grounded in immunohistochemistry, liquid biopsies and next-generation sequencing.

Innovative Therapeutic Approaches for Patients with HER2-Positive Breast Cancer

Overexpression of human epidermal growth factor receptor 2 (HER2), a transmembrane tyrosine kinase receptor, has been described in about 15-20% of breast cancer (BC) and is associated with poor outcomes. Trastuzumab is the first anti-HER2 monoclonal antibody (mAB) that blocks receptor activity but it also activates immune response against cancer cells, thus, revolutionizing the prognosis of patients with HER2-positive BC. Over the years, new therapies have been developed, including other mAbs and tyrosine kinase inhibitors (TKIs) that required multimodal approaches with chemotherapy to optimize their anticancer activity. This chapter gives a comprehensive overview of the last advancements including new approaches and future combinations, which seem to be very promising in overcoming resistance to the traditional anti-HER2 treatments. A modern therapeutic algorithm should include treatment options based on tumour patterns and a patient-centred approach. A proper patient's selection is crucial to derive maximal benefits from a treatment strategy and emerging biomarkers should be integrated along with the HER2 status, which is currently the only validated biomarker in the context of HER2-positive disease. These biomarkers might include molecular features with reported prognostic/predictive significance, such as phosphatidylinositol 3' -kinase (PI3K) or mitogen-activated protein kinase (MAPK) pathways, programmed cell death protein ligand 1 (PD-L1), and tumour-infiltrating lymphocytes (TILs), which all affect prognosis and response to treatments.

The statuses of HER2 expression and mismatch repair in endometrial clear cell carcinoma

High-grade endometrial carcinomas (HGEC) are difficult to classify. With the current use of HER2-based therapy in serous carcinoma, a diagnosis of clear cell carcinoma (CCC) has the potential to exclude patients from receiving therapy. Therefore, we examined HER2 expression in our CCC patients. The preparations of 8 patients with CCC who underwent hysterectomy, bilateral salpingo-oophorectomy, and lymph node dissection were re-evaluated. Patients did not have any prior treatment. Histopathologic parameters that were evaluated include cytoplasmic clearing, nuclear atypia, mitotic activity, hobnail architecture, hyalinized cores, hyaline globules, stratification of epithelial lining papillae, or glandular structures, and highly atypical cell layers. Immunohistochemically, HER2, ER, PR, HNF1β, Napsin A, MLH1, MSH2, MSH6 and PMS2 were applied. HER2 staining pattern, ASCO/CAP protocol used for endometrial carcinom was used. HER2 was positive in 3 of our 8 CCC patients (37.5%). While all of our HER2 + cases were Napsin A and HNF1β positive, MMR proteins were intact and ER and PR were negative. Two patients had wild type p53 and 1 patient had aberrant p53 staining. Considering that there is not always a consensus between SC and CCC, even among gynecopathologists, tumor heterogeneity and different tumor components may exist, and while patients may be diagnosed with CCC and benefit from HER2 therapy, there is also a possibility that they may not benefit from the treatment. The fact that 37.5% of our CCC cases were HER2 + is a finding with strong implications for the therapeutic approach. As a result of our study, in patients with CCC, if MMR is intact and ER-PR is negative, regardless of the p53 staining pattern, HER2 testing may be an objective screening method for patients who are likely to benefit from HER-targeted therapy. Consequently, patients with a diagnosis of CCC can be candidates for future clinical trials of HER2-targeted therapy.

HER2 amplification by next-generation sequencing to identify HER2-positive invasive breast cancer with negative HER2 immunohistochemistry

Background

Human epidermal growth factor receptor 2 (HER2) positive breast carcinomas due to HER2 amplification are associated with aggressive behavior and a poor prognosis. Anti-HER2-targeted therapies are widely used to treat HER2-positive breast carcinomas with excellent outcomes. Accurate identification of HER2 amplification status in breast carcinomas is of important diagnostic and treatment value. Currently, HER2 amplification status is routinely determined by immunohistochemistry (IHC) and/or fluorescence in situ hybridization (FISH) testing. This study will review our past HER2 data to determine and characterize discordant results between HER2 IHC and FISH. It will also determine a potential impact of HER2 amplification status by next-generation sequencing (NGS) on these patients.

Methods

We reviewed a total of 4884 breast carcinomas with coexisting HER2 IHC and HER2 FISH performed at our institution from 2010 to 2022. 57 cases also had a Next-Generation-Sequencing-based (NGS) gene panel performed. Given the advances in biostatic analysis pipelines, NGS methods were utilized to provide results on HER2 amplification status along with somatic mutations.

Results

While the majority (ranging from 98.5% with IHC score of 0 and 93.1% with IHC score of 1 +) of 4884 breast carcinomas had concordant results from HER2 IHC and HER2 FISH testing, a small percentage of patients (ranging from 1.5% in those with IHC score of 0, to 6.9% with IHC score of 1 +) had discordant results, with negative HER2 IHC and positive HER2 FISH results. These patients could be reported as HER2-negative breast carcinomas if only HER2 IHC testing has been performed according to a current cost-effective HER2 test strategy. 57 patients had HER2 amplification status determined by NGS, and all patients had concordant results between HER2 NGS and FISH tests. A HER2-amplified breast carcinoma by NGS had a negative IHC and a positive HER2 FISH result. This case was classified as a HER2-positive breast carcinoma, had anti-HER2-targeted therapy, and achieved a complete clinical response.

Conclusions

A small percentage of HER2-positive breast carcinomas are unidentified because of a negative HER2 IHC based on our current cost-effective HER2 test strategy. It is not feasible and affordable in routine clinical practice to perform HER2 FISH for the cases with negative HER2 IHC (IHC score 0 and 1 +). Therefore, NGS assays capable of simultaneously detecting both somatic mutations and HER2 amplification could provide a more comprehensive genetic profiling for breast carcinomas in a clinical setting. Identification of HER2 amplification by NGS in HER2-positive breast carcinomas with negative HER2 IHC results is important since these cases are concealed by our current cost-effective HER2 test strategy with IHC first (for all cases) and FISH reflex (only for cases with IHC score of 2 +), and would offer the opportunity for potentially beneficial anti-HER2-targeted therapies for these patients.

Loss of HER2 in breast cancer: biological mechanisms and technical pitfalls

Loss of HER2 in previously HER2-positive breast tumors is not rare, occurring in up to 50% of breast cancers; however, clinical research and practice underestimate this issue. Many studies have reported the loss of HER2 after neoadjuvant therapy and at metastatic relapse and identified clinicopathological variables more frequently associated with this event. Nevertheless, the biological mechanisms underlying HER2 loss are still poorly understood. HER2 downregulation, intratumoral heterogeneity, clonal selection, and true subtype switch have been suggested as potential causes of HER2 loss, but translational studies specifically investigating the biology behind HER2 loss are virtually absent. On the other side, technical pitfalls may justify HER2 loss in some of these samples. The best treatment strategy for patients with HER2 loss is currently unknown. Considering the prevalence of this phenomenon and its apparent correlation with worse outcomes, we believe that correlative studies specifically addressing HER2 loss are warranted.

The role of HER2 alterations in clinicopathological and molecular characteristics of breast cancer and HER2-targeted therapies: a comprehensive review

Breast cancer (BC) is the most common malignancy in women and one of the leading causes of cancer mortality, despite significant treatment advancements over the last decades. Human epidermal growth factor receptor-2 (HER2) is a member of the ERBB family of receptor tyrosine kinases which have long been known to mediate cancer cell growth and invasion through constitutive activation of oncogenic downstream signaling, such as PI3K/Akt/mTOR and MAPK. Overexpression/amplification of HER2 in various tumors, especially BC, offers the possible therapeutic potential for target therapies. HER2-targeted therapies, either with a combination of chemotherapy or through multi-anti-HER2 therapies without chemotherapy, have significantly improved the prognosis of HER2-positive tumors. In recent years, novel anti-HER2 agents and combination therapies have garnered much attention, especially for heavily treated advanced or metastatic BCs. HER2-positive BC is biologically a heterogeneous group depending on HER2 activation mechanisms, hormone receptor status, genome variations, tumor heterogeneity, and treatment resistance, which affect the treatment benefit and patients' outcomes. This review will discuss HER2 alternations (gene amplification or receptor overexpression) in BC, their correlation with clinicopathological characteristics and molecular characteristics, and HER2-based therapies in tumors with HER2 overexpression/amplification.

Indian Data on HER2 Fluorescence In Situ Hybridization in Invasive Breast Cancer with Immunohistochemically Equivocal Results As Per 2018 ASCO/CAP Guidelines

Biren ParikhIntroduction  Hormonal status and HER2 expression are valuable biomarkers and dictate the management of the patients diagnosed with invasive breast cancer (IBC). It is crucial to identify the patients who truly respond to anti-HER2 targeted therapy. Updated 2018 American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines has recommended certain modifications in HER2 interpretation by fluorescence in situ hybridization (FISH) with concomitant immunohistochemistry (IHC). Objectives  We aimed to evaluate HER2 FISH interpretation in IBC with equivocal IHC results as per 2018 ASCO/CAP recommendations and compare FISH results with hormonal receptor status. Materials and Methods  FISH results of 502 cases of IBC with equivocal IHC report between January 2016 to January 2022 were reviewed retrospectively. FISH results were categorized according to ASCO/CAP guidelines 2018 into five respective groups. Results  FISH testing in IHC equivocal cases showed 219 (43.6%) cases were classic amplified (positive) belonged to group 1, 217(43.2%) cases were classic nonamplified (negative) fell into group 5, 39 (7.8%) and 02 (0.4%) patients were in group 2 (negative) and group 3 (positive), and 25 (5.0%) cases were in group 4 (negative). About 52.1 and 49.3% of cases with estrogen receptor and progesterone receptor positivity were reported as HER2 positive. Among 502 cases, 25 equivocal cases according to the 2013 guidelines were redefined as HER2 negative and 02 (0.4%) cases reported positive were classified negative as per updated 2018 guidelines. Conclusion  Revised 2018 guidelines is helpful in accurate identification of HER2 status and in avoiding targeted therapy in unwarranted cases. Updated 2018 guidelines has removed equivocal HER2-FISH category that has eliminated management dilemma in these cases. Only long-term clinical follow-up will establish the validity of the updated guidelines.

The frequency and clinical significance of centromere enumeration probe 17 alterations in HER2 immunohistochemistry-equivocal invasive breast cancer

Background and aims

Chromosome 17 alterations affect the assessment of HER2 gene amplification in breast cancer (BC), but its clinical significance remains unclear. This study aimed to identify the prevalence of centromere enumeration probe 17 (CEP17) alterations, and its correlation with response to neoadjuvant therapy (NAT) in BC patients with human epidermal growth factor receptor 2 (HER2) immunohistochemistry‐equivocal score.

Methods and results

A large BC cohort (n = 6049) with HER2 immunohistochemistry score 2+ and florescent in‐situ hybridisation (FISH) results was included to assess the prevalence of CEP17 alterations. Another cohort (n = 885) with available clinicopathological data was used to evaluate the effect of CEP17 in the setting of NAT. HER2‐amplified tumours with monosomy 17 (CEP17 copy number < 1.5 per nucleus), normal 17 (CEP17 1.5–< 3.0) and polysomy 17 (CEP17 ≥ 3.0) were observed in 16, 59 and 25%, respectively, compared with 3, 74 and 23%, respectively, in HER2‐non‐amplified tumours. There was no significant relationship between CEP17 alterations and pathological complete response (pCR) rate in both HER2‐amplified and HER2‐non‐amplified tumours. The independent predictors of pCR were oestrogen (ER) negativity in HER2‐amplified tumours [ER negative versus positive; odds ratio (OR) = 11.80; 95% confidence interval (CI) = 1.37–102.00; P = 0.02], and histological grade 3 in HER2 non‐amplified tumours (3 versus 1, 2; OR = 5.54; 95% CI = 1.61–19.00; P = 0.007).

Conclusion

The impacts of CEP17 alterations are not as strong as those of HER2/CEP17 ratio and HER2 copy number. The hormonal receptors status and tumour histological grade are more useful to identify BC patients with a HER2 immunohistochemistry‐equivocal score who would benefit from NAT.

Computer-Aided Scoring Of () Gene Amplification Status In Breast Cancer

Background

Identification of HER2 protein overexpression and/or amplification of the HER2 gene are required to qualify breast cancer patients for HER2 targeted therapies. In situ hybridization (ISH) assays that identify HER2 gene amplification function as a stand-alone test for determination of HER2 status and rely on the manual quantification of the number of HER2 genes and copies of chromosome 17 to determine HER2 amplification.

Methods

To assist pathologists, we have developed the uPath HER2 Dual ISH Image Analysis for Breast (uPath HER2 DISH IA) algorithm, as an adjunctive aid in the determination of HER2 gene status in breast cancer specimens. The objective of this study was to compare uPath HER2 DISH image analysis vs manual read scoring of VENTANA HER2 DISH-stained breast carcinoma specimens with ground truth (GT) gene status as the reference. Three reader pathologists reviewed 220, formalin-fixed, paraffin-embedded (FFPE) breast cancer cases by both manual and uPath HER2 DISH IA methods. Scoring results from manual read (MR) and computer-assisted scores (image analysis, IA) were compared against the GT gene status generated by consensus of a panel of pathologists. The differences in agreement rates of HER2 gene status between manual, computer-assisted, and GT gene status were determined.

Results

The positive percent agreement (PPA) and negative percent agreement (NPA) rates for image analysis (IA) vs GT were 97.2% (95% confidence interval [CI]: 95.0, 99.3) and 94.3% (95% CI: 90.8, 97.3) respectively. Comparison of agreement rates showed that the lower bounds of the 95% CIs for the difference of PPA and NPA for IA vs MR were –0.9% and –6.2%, respectively. Further, inter- and intra-reader agreement rates in the IA method were observed with point estimates of at least 96.7%.

Conclusions

Overall, our data show that the uPath HER2 DISH IA is non-inferior to manual scoring and supports its use as an aid for pathologists in routine diagnosis of breast cancer.

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Image analysis algorithm for HER2 amplification using Bright-field ISH in Breast.

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Automated tumor cell selection and quantitation within pathologist defined ROI.

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The image analysis algorithm is non-inferior to manual scoring.

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Integrated solution to support pathologists in determining HER2 gene status.

Digital Imaging Correlation of Immunohistochemistry and Fluorescence in Situ Hybridization in Breast Carcinoma Cases with HER2 Genetic Heterogeneity

Genetic Heterogeneity (GH) is a rare but important event in evaluation of HER2 amplification status. We investigated whether HER2 FISH Genetic Heterogeneity (GH) correlated with increased protein expression by immunohistochemistry (IHC) and/or morphologic features using image analyses. Retrospective search of HER2 FISH GH cases 2016-2020 was performed. Cases with both FISH and IHC slides available were considered eligible and were digitally imaged. Additional demographic, histological, and treatment information was compiled from pathology and medical records when available. Overall, 11/15 (73.3%) of the cases had HER2 FISH GH that matched to areas of HER2 over-expression or focally different morphology. Nine cases with areas of gene amplification overlapped with <10% of intense circumferential protein expression ("Mini 3+,"), and one case with focal micropapillary features. Clinical information was available on 6 (40%) patients, all were alive with no evidence of disease (mean follow up 30. 5 months; range 12-65 months). One patient with GH and a lymph node metastasis showed non-amplified population in the nodal tumor. GH when defined as discrete clusters of amplified cells following 2013 ASCO/CAP guidelines, -even when less than 10 % of the tumor cells-frequently has morphologic correlates such as focal intense protein overexpression or micropapillary morphology. Clinical significance of these focal gene amplification and protein over-expression needs to be further investigated.

HER2 copy number quantification in primary tumor and cell-free DNA provides additional prognostic information in HER2 positive early breast cancer

Background

The quantitative relationship between HER2 copy number and prognosis in HER2 positive adjuvant setting remain controversial, and few studies have focused on adjuvant setting to illustrate the potential clinical relevance of HER2 in cfDNA. Our study aim to develop a novel method in HER2 quantification and explore the relationship between HER2 copy number in primary tumors or cfDNA and prognosis in HER2 positive early breast cancer.

Methods

Two hundred and two patients with early breast cancer were prospectively included in a study where primary tumors, matching non-cancer breast tissue, corresponding plasma, and the plasma from 20 healthy volunteers were collected. Cox proportional hazard analysis was employed to determine the prognostic value of HER2 gene copy number in tissue and cfDNA. Tissue based nomograms and time-dependent decision curve analysis were used to evaluate the practicality of HER2 copy number stratification.

Results

HER2 amplification by CNVplex demonstrated a robust concordance with FISH (concordance 89.2%). A three-tiered system of tissue and a two-tiered system of cfDNA classification were shown to be independent prognostic factors. A tissue copy number-based nomogram was fitted and further evaluation revealed a good performance in discrimination (c statistic 0.801) and calibration.

Conclusions

We first report CNVplex as a viable alternative for HER2 detection. Quantitative evaluation of HER2 presents tremendous potential for use in risk stratification. We also uncover the potential for using HER2 copy number in cfDNA as a biomarker for prognosis in a HER2 positive adjuvant setting.

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CNVplex was developed to quantify HER2 copy number.

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HER2 copy number of primary tumor present quantitative relationship with prognosis in HER2 positive early breast cancer.

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HER2 copy number of cfDNA could function as a biomarker for prognosis.

Clinical Outcomes of Neoadjuvant Therapy in Human Epidermal Growth Factor Receptor 2 Breast Cancer Patients: A Single-Center Retrospective Study

(1) Background: Neoadjuvant therapy is widely used to treat locally advanced breast cancer. It has been recently shown that it can also improve the prognosis of patients during the early stages of breast cancer. In the past, advanced breast cancer with positive Human Epidermal growth factor Receptor 2 (HER2+) resulted in poor prognoses; however, outcomes have since changed after the introduction of HER2-targeting therapy. Achieving pathological Complete Response (pCR) is the most important aim, as it is a predictor of long-term outcomes in high-risk breast cancer subtypes. (2) Methods: We performed a retrospective review of all breast cancer patients who were treated with neoadjuvant therapy at Taichung Veterans General Hospital (VGHTC) between 2010 and 2018. A total of 147 HER2+ breast cancer patients who underwent neoadjuvant chemotherapy involving anthracycline and taxane-based regimens were enrolled. Within that population, 95 and 52 cases received single-blockade (Trastuzumab) and dual-blockade (Trastuzumab and Pertuzumab) neoadjuvant anti-HER2 therapy, respectively. (3) Results: The dual-blockade therapy group displayed a significantly higher pCR rate after surgery as compared to the single-blockade group (63.5% vs. 43.2%, p = 0.019). Advanced stage, larger tumor size, lymph node involvement and HER2 expression status were associated with the pCR rate. The 4-year OS was 85.2% and 100% in the single-blockage and dual-blockade therapy groups, respectively (p = 0.041). (4) Conclusion: Anthracycline, followed by taxane-based neoadjuvant chemotherapy combined with the dual HER2-blockade, had a higher pCR rate and better outcome when compared with the single HER2-blockade strategy in locally advanced HER2 breast cancer.

HER2-Low Breast Cancers

OBJECTIVES

Recent clinical trials have demonstrated significant clinical benefits from novel therapeutic compounds in breast cancer patient with human epidermal growth factor receptor 2 (HER2) immunohistochemical (IHC) score of 1+ or 2+ and negative in situ hybridization (ISH) result. A new concept of "HER2-low" breast cancer has been proposed and applied in the recent and ongoing clinical trials. In this article, we review the literature on the topic of HER2-low breast cancer.

METHODS

A literature search in PubMed was performed using key words related to HER2-low breast cancer. Major relevant studies that were presented in international breast cancer conferences were also included.

RESULTS

HER2-low breast cancer is currently defined as breast cancer with HER2 IHC score of 1+ or 2+ and negative ISH result. It likely represents a group of tumors with significant biological heterogeneity. Reports of clinical activity using the next generation of HER2-targeting antibody-drug conjugates in HER2-low breast cancers suggest that some strategies of targeting HER2 might be effective in this patient population while raising considerable concerns over limitations in our current testing methodologies and our ability to accurately identify such patients.

CONCLUSIONS

The promising efficacy of novel HER2-targeted therapy in advanced HER2-low breast cancers has raised the possibility for changing the clinical interpretation of HER2 status in breast cancer to include a HER2-low category; however, the definition of HER2-low breast cancer, the corresponding reliable and accurate quantitative HER2 testing methodology, and the biology of HER2-low breast cancer remain poorly defined.

Anti-HER2 therapy in metastatic breast cancer: many choices and future directions

Metastatic HER2 + breast cancer is an expanding area of drug development and research, with three new drugs approved in 2020 alone. While first-line therapy is well-established for metastatic HER2 + breast cancer, the standard of care for second-line therapy will likely be changing soon based on the results of the DESTINY-Breast03 trial. In the third-line setting, many options are available. Considerations in choosing between regimens in the third-line include resistance to trastuzumab, the presence of brain metastases, and tolerability. High rates of resistance exist in this setting particularly due to expression of p95, a truncated form of HER2 that constitutively activates downstream signaling pathways. We suggest a tyrosine kinase inhibitor (TKI)-based regimen because of the activity of TKIs in brain metastases and in p95-expressing tumors. Attempts to overcome resistance to anti-HER2 therapies with PI3K inhibitors, mTOR inhibitors, and CDK 4/6 inhibitors are an active area of research. In the future, biomarkers are needed to help predict which therapies patients may benefit from the most. We review the many new drugs in development, including those with novel mechanisms of action.

Updates on breast biomarkers

Recent advancements in breast cancer treatment have ushered in a new era of precision medicine. Novel trials have led to the approval of a growing list of personalized therapies and corresponding biomarkers. These advancements have shifted the pathologist's practice into a leading role in the management breast cancer. Understanding the complex algorithms and diagnostic modalities used to assess predictive and prognostic biomarkers is central for quality oncology care. ER and HER2 subcategorize breast cancers into treatment groups under which different biomarkers and therapies are indicated, while they also serve as predictive biomarkers for specific targeted treatments. This review will cover the evolution and latest updates of the CAP/ASCO guidelines relevant to these two important biomarkers in breast cancer. Still evolving concepts such as HER2 heterogeneity, HER2 "low," and HER2-mutated cancers have the potential to continue to change HER2 testing in breast cancers. In addition to ER and HER2, biomarkers used in specific clinical scenarios will be covered. In early-stage ER-positive/HER2-negative disease, multi-gene expression panels (such as OncotypeDX) have emerged as the new standard biomarker when determining if chemotherapy should be added to endocrine therapy. In the more aggressive ER-negative/HER2-positive or triple negative early-stage breast cancers, response to neoadjuvant therapy has proved to be a useful biomarker to help determine if additional therapy should be added for patients with an incomplete response. Ki67 has also recently emerged as a marker that can be used to identify the highest risk ER-positive and HER2-negative cancers if considering adding a cell cycle inhibitor (abemaciclib) to endocrine therapy. Importantly, in the metastatic setting, numerous predictive biomarkers have emerged, including recommendations for germline BRCA mutation testing for all metastatic patients (to determine if PARP inhibitor therapy is an option) and other ER-/HER2-dependent biomarkers such as PD-L1 (for potential immunotherapy in triple negative patients) and PIK3CA mutation status (for potential PI3K inhibitor therapy in ER-positive metastatic patients). Other less common biomarkers of targeted therapy options (e.g., MSI/MMR, TMB, NTRK) as well as comprehensive genomic profiling to identify uncommon targets are also available in the metastatic setting to determine additional treatment options.

Single HER2-positive tumor cells are detected in initially HER2-negative breast carcinomas using the DEPArray™-HER2-FISH workflow

Background

In breast cancer (BC), overexpression of HER2 on the primary tumor (PT) is determined by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH) to stratify samples as negative, equivocal and positive to identify patients (pts) for anti-HER2 therapy. CAP/ASCO guidelines recommend FISH for analyzing HER2/neu (ERBB2) gene amplification and for resolving equivocal HER2 IHC results. However, pre-analytical and analytical aspects are often confounded by sample related limitations and tumor heterogeneity and HER2 expression may differ between the PT and circulating tumor cells (CTCs), the precursors of metastasis. We used a validation cohort of BC patients to establish a new DEPArray™-PT-HER2-FISH workflow for further application in a development cohort, characterized as PT-HER2-negative but CTC-HER2/neu-positive, to identify patients with PT-HER2 amplified cells not detected by routine pathology.

Methods

50 µm FFPE tumor curls from the validation cohort (n = 49) and the development cohort (n = 25) underwent cutting, deparaffinization and antigen retrieval followed by dissociation into a single-cell suspension. After staining for cytokeratin, vimentin, DAPI and separation via DEPArray™, single cells were processed for HER2-FISH analysis to assess the number of chromosome 17 and HER2 loci signals for comparison, either with available IHC or conventional tissue section FISH. CTC-HER2/neu status was determined using the AdnaTest BreastCancer (QIAGEN, Hilden, Germany).

Results

Applying CAP/ASCO guidelines for HER2 evaluation of single PT cells, the comparison of routine pathology and DEPArray™-HER2-FISH analysis resulted in a concordance rate of 81.6% (40/49 pts) in the validation cohort and 84% (21/25 pts) in the development cohort, respectively. In the latter one, 4/25 patients had single HER2-positive tumor cells with 2/25 BC patients proven to be HER2-positive, despite being HER2-negative in routine pathology. The two other patients showed an equivocal HER2 status in the DEPArray™-HER2-FISH workflow but a negative result in routine pathology. Whereas all four patients with discordant HER2 results had already died, 17/21 patients with concordant HER2 results are still alive.

Conclusions

The DEPArray™ system allows pure tumor cell recovery for subsequent HER2/neu FISH analysis and is highly concordant with conventional pathology. For PT-HER2-negative patients, harboring HER2/neu-positive CTCs, this approach might allow caregivers to more effectively offer anti-HER2 treatment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12282-022-01330-8.

Intratumoral Heterogeneity and Immune Response Indicators to Predict Overall Survival in a Retrospective Study of HER2-Borderline (IHC 2+) Breast Cancer Patients

Breast cancer (BC) categorized as human epidermal growth factor receptor 2 (HER2) borderline [2+ by immunohistochemistry (IHC 2+)] presents challenges for the testing, frequently obscured by intratumoral heterogeneity (ITH). This leads to difficulties in therapy decisions. We aimed to establish prognostic models of overall survival (OS) of these patients, which take into account spatial aspects of ITH and tumor microenvironment by using hexagonal tiling analytics of digital image analysis (DIA). In particular, we assessed the prognostic value of Immunogradient indicators at the tumor–stroma interface zone (IZ) as a feature of antitumor immune response. Surgical excision samples stained for estrogen receptor (ER), progesterone receptor (PR), Ki67, HER2, and CD8 from 275 patients with HER2 IHC 2+ invasive ductal BC were used in the study. DIA outputs were subsampled by HexT for ITH quantification and tumor microenvironment extraction for Immunogradient indicators. Multiple Cox regression revealed HER2 membrane completeness (HER2 MC) (HR: 0.18, p = 0.0007), its spatial entropy (HR: 0.37, p = 0.0341), and ER contrast (HR: 0.21, p = 0.0449) as independent predictors of better OS, with worse OS predicted by pT status (HR: 6.04, p = 0.0014) in the HER2 non-amplified patients. In the HER2-amplified patients, HER2 MC contrast (HR: 0.35, p = 0.0367) and CEP17 copy number (HR: 0.19, p = 0.0035) were independent predictors of better OS along with worse OS predicted by pN status (HR: 4.75, p = 0.0018). In the non-amplified tumors, three Immunogradient indicators provided the independent prognostic value: CD8 density in the tumor aspect of the IZ and CD8 center of mass were associated with better OS (HR: 0.23, p = 0.0079 and 0.14, p = 0.0014, respectively), and CD8 density variance along the tumor edge predicted worse OS (HR: 9.45, p = 0.0002). Combining these three computational indicators of the CD8 cell spatial distribution within the tumor microenvironment augmented prognostic stratification of the patients. In the HER2-amplified group, CD8 cell density in the tumor aspect of the IZ was the only independent immune response feature to predict better OS (HR: 0.22, p = 0.0047). In conclusion, we present novel prognostic models, based on computational ITH and Immunogradient indicators of the IHC biomarkers, in HER2 IHC 2+ BC patients.

[2021 update of the GEFPICS' recommendations for HER2 status assessment in invasive breast cancer in France]

The last international guidelines on HER2 determination in breast cancer have been updated in 2018 by the American Society of Clinical Oncology and College of American Pathologists, on the basis of a twenty-year practice and results of numerous clinical trials. Moreover, the emerging HER2-low concept for 1+ and 2+ non amplified breast cancers lead to refine French practices for HER2 status assessment. The GEFPICS group, composed of expert pathologists, herein presents the latest French recommendations for HER2 status evaluation in breast cancer, taking into account the ASCO/CAP guidelines and introducing the HER2-low concept. In the era of personalized medicine, HER2 status assessment remains one of the most important biomarkers in breast cancer and its quality guaranties the optimal patients' care. French pathologists' commitment in theranostic biomarker quality is more than ever required to provide the most efficient cares in oncology.

Detailed Reanalysis of 500 Breast Cancers With Equivocal HER2 Immunohistochemistry and Borderline ERBB2 Fluorescence In Situ Hybridization Results

OBJECTIVES

We investigated the impact of our laboratory's reflex testing process for resolving ERBB2 (HER2) status on breast cancer samples that require additional workup after fluorescence in situ hybridization (FISH), per guideline recommendations published in 2018 by the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP).

METHODS

In total, 500 breast cancer specimens with ERBB2 FISH results in groups 2 through 4 (all reported as immunohistochemistry [IHC] equivocal [2+] at external laboratories) were resubmitted for IHC testing in our laboratory. Per the ASCO/CAP guideline, FISH was rescored when internal IHC was also equivocal (2+), targeted to tumor areas demonstrating more intense IHC staining, if observed.

RESULTS

Reflex IHC/FISH testing changed the final reported ERBB2 status in 185 of 500 (37.0%) samples. Result changes included discordant IHC (n = 4 score 0, n = 132 score 1+, and n = 16 score 3+) and discordant FISH (n = 33). Numerical differences in FISH scores were comparable for targeted vs nontargeted FISH rescoring (P = .086 for ERBB2 copy number; P = .49 for ERBB2 ratio). Two cases showed larger differences in FISH scores, suggesting heterogeneity.

CONCLUSIONS

Retesting of breast cancer samples with equivocal IHC frequently changes IHC results, but targeted reanalysis of borderline FISH results rarely identifies significant differences in ERBB2 copy number or ratio.

Impact of HER2 Heterogeneity on Treatment Response of Early-Stage HER2-Positive Breast Cancer: Phase II Neoadjuvant Clinical Trial of T-DM1 Combined with Pertuzumab

Intratumor heterogeneity is postulated to cause therapeutic resistance. To prospectively assess the impact of HER2 (ERBB2) heterogeneity on response to HER2-targeted therapy, we treated 164 patients with centrally confirmed HER2-positive early-stage breast cancer with neoadjuvant trastuzumab emtansine plus pertuzumab. HER2 heterogeneity was assessed on pretreatment biopsies from two locations of each tumor. HER2 heterogeneity, defined as an area with ERBB2 amplification in >5% but <50% of tumor cells, or a HER2-negative area by FISH, was detected in 10% (16/157) of evaluable cases. The pathologic complete response rate was 55% in the nonheterogeneous subgroup and 0% in the heterogeneous group (P < 0.0001, adjusted for hormone receptor status). Single-cell ERBB2 FISH analysis of cellular heterogeneity identified the fraction of ERBB2 nonamplified cells as a driver of therapeutic resistance. These data suggest HER2 heterogeneity is associated with resistance to HER2-targeted therapy and should be considered in efforts to optimize treatment strategies. SIGNIFICANCE: HER2-targeted therapies improve cure rates in HER2-positive breast cancer, suggesting chemotherapy can be avoided in a subset of patients. We show that HER2 heterogeneity, particularly the fraction of ERBB2 nonamplified cancer cells, is a strong predictor of resistance to HER2 therapies and could potentially be used to optimize treatment selection.See related commentary by Okines and Turner, p. 2369.This article is highlighted in the In This Issue feature, p. 2355.

Systematic tissue collection during clinical breast biopsy is feasible, safe and enables high-content translational analyses

Systematic collection of fresh tissues for research at the time of diagnostic image-guided breast biopsy has the potential to fuel a wide variety of innovative studies. Here we report the initial experience, including safety, feasibility, and laboratory proof-of-principle, with the collection and analysis of research specimens obtained via breast core needle biopsy immediately following routine clinical biopsy at a single institution over a 14-month period. Patients underwent one or two additional core biopsies following collection of all necessary clinical specimens. In total, 395 patients were approached and 270 consented to the research study, yielding a 68.4% consent rate. Among consenting patients, 238 lesions were biopsied for research, resulting in 446 research specimens collected. No immediate complications were observed. Representative research core specimens showed high diagnostic concordance with clinical core biopsies. Flow cytometry demonstrated consistent recovery of hundreds to thousands of viable cells per research core. Among a group of HER2 + tumor research specimens, HER2 assessment by flow cytometry correlated highly with immunohistochemistry (IHC) staining, and in addition revealed extensive inter- and intra-tumoral variation in HER2 levels of potential clinical relevance. Suitability for single-cell transcriptomic analysis was demonstrated for a triple-negative tumor core biopsy, revealing substantial cellular diversity in the tumor immune microenvironment, including a prognostically relevant T cell subpopulation. Thus, collection of fresh tissues for research purposes at the time of diagnostic breast biopsy is safe, feasible and efficient, and may provide a high-yield mechanism to generate a rich tissue repository for a wide variety of cross-disciplinary research.

Targeting HER2 heterogeneity in breast cancer

The identification of Human epidermal growth factor receptor 2 (HER2) as a target in breast cancer and the subsequent development of HER2-targeted therapies has revolutionized the treatment of patients with HER2-positive breast cancer. However, there is an increasing awareness of how frequently tumors have low or heterogeneous expression of HER2. It is now recognized that this impacts the degree of benefit from HER2-targeted therapies. With the advent of novel and more potent antibody drug conjugates, targeting HER2 in traditional HER2-negative tumors with "HER2-low" expression is becoming possible. It is essential to refine the nomenclature around HER2 expression to enable clinicians to optimize treatment for patients across the HER2 expression spectrum in breast cancer. HER2 heterogeneity can be detected by conventional IHC, gene expression profiling or other methods and numerous studies have documented the correlation between the presence of HER2 heterogeneity and shorter disease-free survival (DFS) and overall survival (OS). Validation of techniques to identify HER2 heterogeneity in the clinic and concurrent development of agents to effectively treat tumors with non-uniform HER2 expression is needed.

Comprehensive analysis of the cancer driver genes in breast cancer demonstrates their roles in cancer prognosis and tumor microenvironment

Background

Breast cancer is the most common malignancy in women. Cancer driver gene-mediated alterations in the tumor microenvironment are critical factors affecting the biological behavior of breast cancer. The purpose of this study was to identify the expression characteristics and prognostic value of cancer driver genes in breast cancer.

Methods

The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) datasets are used as the training and test sets. Classified according to cancer and paracancerous tissues, we identified differentially expressed cancer driver genes. We further screened prognosis-associated genes, and candidate genes were submitted for the construction of a risk signature. Functional enrichment analysis and transcriptional regulatory networks were performed to search for possible mechanisms by which cancer driver genes affect breast cancer prognosis.

Results

We identified more than 200 differentially expressed driver genes and 27 prognosis-related genes. High-risk group patients had a lower survival rate compared to the low-risk group (P<0.05), and risk signature showed high specificity and sensitivity in predicting the patient prognosis (AUC 0.790). Multivariate regression analysis suggested that risk scores can independently predict patient prognosis. Further, we found differences in PD-1 expression, immune score, and stromal score among different risk groups.

Conclusion

Our study confirms the critical prognosis role of cancer driver genes in breast cancer. The cancer driver gene risk signature may provide a novel biomarker for clinical treatment strategy and survival prediction of breast cancer.

HER2 Testing in Endometrial Serous Carcinoma: Time for Standardized Pathology Practice to Meet the Clinical Demand

CONTEXT.—

Endometrial serous carcinoma is an aggressive subtype of endometrial cancer with the highest rate of recurrence and mortality among all histotypes. A recent clinical trial showed prolonged progression-free survival in advanced-stage and recurrent human epidermal growth factor receptor 2 (HER2)-positive endometrial serous carcinoma when trastuzumab was added to the standard chemotherapy regimen. This targeted therapeutic approach was recently endorsed by the National Comprehensive Cancer Network clinical guidelines. There is a growing interest among clinicians to obtain HER2 testing in endometrial serous carcinoma, and pathologists need to be prepared to recognize the unique characteristics of HER2 protein expression and gene amplification in these tumors and apply specific HER2 scoring criteria.

OBJECTIVE.—

To provide a historical overview of targeted HER2 therapy in endometrial serous carcinoma and to summarize key findings from recent studies on the specific features of HER2 protein expression and gene amplification relative to other tumor types. Endometrial carcinoma-specific HER2 testing criteria are proposed based on evidence in the existing literature.

DATA SOURCES.—

Sources comprise review of the literature and personal experience of the author.

CONCLUSIONS.—

HER2 protein overexpression and/or gene amplification is present in approximately 25% to 30% of endometrial serous carcinomas, providing an opportunity for targeted therapy. Pathologists play a key role in tumor HER2 testing and scoring to ensure appropriate patient selection and successful clinical outcome.

HER2 in situ hybridization test in breast cancer: quantifying margins of error and genetic heterogeneity

The aim of the present study was to evaluate the effect of counting increasing number of invasive cancer cells in the result of the HER2 in situ hybridization (ISH) test in breast cancer as well as to compare two different approaches of measuring genomic heterogeneity (single cell and population based). A cohort of 100 consecutive breast cancer cases (primary and metastatic) were evaluated for HER2 gene amplification with bright-field ISH. The evaluation of the samples included scoring 20 nuclei, in five different areas, measuring the margins of error for each case. Genomic heterogeneity (GH) was defined by the 2018 ASCO/CAP guideline as a discrete population of tumor cells with HER2 amplification. We also evaluated GH as single tumor cells with HER2 amplification. The stabilization of the coefficient of variation of HER2/CEP17 ratio requires about 60 invasive cancer cells. The average margin of error of HER2/CEP17 ratio and of HER2 copy number was 0.40 and 0.53, respectively, when counting 20 cells, decreasing to 0.20 and 0.26 when counting 100 cells. Population GH was observed in 1% of the cases, while single cell GH was observed in 27% of the cases, reaching its maximum value in cases near the thresholds of positivity. Therefore, margins of error in HER2 ISH test are high, and the minimal cell number recommended in current guidelines should be raised to at least 60 cells. Population GH is a rare event and single cell GH is maximal in cases near the thresholds.

HER2 Testing Characteristics Can Predict Residual Cancer Burden following Neoadjuvant Chemotherapy in HER2-Positive Breast Cancer

Objectives

The response to HER2-targeted neoadjuvant chemotherapy (NAC) in HER2-positive (+) breast cancer can be quantified using residual cancer burden (RCB) pathologic evaluation to predict relapse free/overall survival. However, more information is needed to characterize the relationship between patterns of HER2 testing results and response to NAC. We evaluated clinicopathologic characteristics associated with RCB categories in HER2+ patients who underwent HER2-directed NAC.

Methods

A retrospective chart review was conducted with Stage I-III HER2+ breast cancer cases following NAC and surgical resection. HER2 immunohistochemistry (IHC) staining and fluorescence in situ hybridization (FISH), histologic/clinical characteristics, hormone receptor status, and RCB scores (RCB-0, RCB-I, RCB-II, and RCB-III) were evaluated.

Results

64/151 (42.4%) patients with HER2+ disease had pathologic complete response (pCR). Tumors with suboptimal response (RCB-II and RCB-III) were more likely to demonstrate less than 100% HER2 IHC 3+ staining (p < 0.0001), lower HER2 FISH copies (p < 0.0001), and lower HER2/CEP17 ratios (p = 0.0015) compared to RCB-I and RCB-II responses. Estrogen receptor classification using ≥10% versus ≥1% staining showed greater association with higher RCB categories.

Conclusions

HER2+ characteristics show differing response to therapy despite all being categorized as positive; tumors with less than 100% IHC 3+ staining, lower HER2 FISH copies, and lower HER2/CEP17 ratios resulted in higher RCB scores.

Clinical significance of quantitative categorization of HER2 fluorescent in situ hybridization results in invasive breast cancer patients treated with HER2-targeted agents

HER2 (ERBB2) gene status serves as a strong predictive marker of response to HER2-targeted agents in invasive breast cancers, albeit with heterogeneous response. Our aim was to determine the distribution and prognosis of HER2 groups by fluorescent in situ hybridization (FISH) using the updated 2018 American Society of Clinical Oncology-College of American Pathologist (ASCO-CAP) guidelines. We identified 226 cases of equivocal or positive HER2 FISH invasive breast cancer (interpreted by ASCO-CAP guidelines at the time of reporting) who received HER2-targeted agents from 2006 to 2017. We subcategorized Group 1 further into three subgroups: low amplified (HER2/CEP17 ratio ≥ 2.0-2.99, mean HER2/cell 4.0-5.9), amplified (HER2/CEP17 ratio ≥ 2.0-2.99, mean HER2/cell ≥ 6), and excessive amplification (HER2/CEP17 ratio ≥ 3.0, mean HER2/cell ≥ 4.0). Outcomes studied were recurrence, metastasis, second breast primary, disease-specific survival (DSS), and overall survival (OS). Univariate analysis showed that the five categories of HER2 FISH were significantly associated with OS (p < 0.01), specifically higher HER2 amplification was associated with fewer deaths. HER2 FISH status also statistically significantly relates to DFS (p < 0.01) and metastasis (p = 0.01) but not with recurrence or second breast primary in our study. Tumor type and HER2 ISH Groups are independent predictors for both OS and DFS in our cohort. The proposed Group 1 subcategories were significantly associated with OS (p < 0.01) and DFS (p < 0.01), excessive HER2 amplification was associated with longer median survival. The Cox regression models showed better survival outcomes for the excessive amplification subgroup than the low amplified subgroup, with OS (hazard ratio = 0.63, 95% CI 0.42-0.93) and DFS (HR = 0.55, 95% CI 0.37-0.83). We demonstrated that in HER2 FISH Group 1 patients, high HER2 amplification was significantly associated with longer OS and DFS; these patients seem to benefit more from HER2-targeted regimens. We recommend reporting these Group 1 subcategories when assessing HER2 FISH.

Detection of ERBB2 amplification in uterine serous carcinoma by next-generation sequencing: an approach highly concordant with standard assays

Uterine serous carcinoma is an aggressive subtype of endometrial cancer that accounts for fewer than 10% of endometrial carcinomas but is responsible for about half of deaths. A subset of cases has HER2 overexpression secondary to ERBB2 gene amplification, and these patients may benefit from anti-HER2 therapies, such as trastuzumab. HER2 protein overexpression is currently assessed by immunohistochemistry (IHC) and ERBB2 gene amplification by fluorescence in situ hybridization (FISH). Targeted next-generation sequencing (NGS) is increasingly used to routinely identify predictive and prognostic molecular abnormalities in endometrial carcinoma. To investigate the ability of a targeted NGS panel to detect ERBB2 amplification, we identified cases of uterine serous carcinoma (n = 93) and compared HER2 expression by IHC and copy number assessed by FISH with copy number status assessed by NGS. ERBB2 copy number status using a combination of IHC and FISH was interpreted using the 2018 ASCO/CAP guidelines for breast carcinoma. ERBB2 amplification by NGS was determined by the relative number of reads mapping to ERBB2 in tumor DNA compared to control nonneoplastic DNA. Cases with copy number ≥6 were considered amplified and copy number <6 were non-amplified. By IHC, 70 specimens were classified as negative (0 or 1+), 19 were classified as equivocal (2+), and 4 were classified as positive (3+). Using combined IHC/FISH, ERBB2 amplification was observed in 8 of 93 cases (9%). NGS identified the same 8 cases with copy number ≥6; all 85 others had copy number <6. In this series, NGS had 100% concordance with combined IHC/FISH in identifying ERBB2 amplification. NGS is highly accurate in detecting ERBB2 amplification in uterine serous carcinoma and provides an alternative to measurement by IHC and FISH.