Genetic heterogeneity in HER2 testing may influence therapy eligibility

Dual attention model with reinforcement learning for classification of histology whole-slide images

Digital whole slide images (WSIs) are generally captured at microscopic resolution and encompass extensive spatial data (several billions of pixels per image). Directly feeding these images to deep learning models is computationally intractable due to memory constraints, while downsampling the WSIs risks incurring information loss. Alternatively, splitting the WSIs into smaller patches (or tiles) may result in a loss of important contextual information. In this paper, we propose a novel dual attention approach, consisting of two main components, both inspired by the visual examination process of a pathologist: The first soft attention model processes a low magnification view of the WSI to identify relevant regions of interest (ROIs), followed by a custom sampling method to extract diverse and spatially distinct image tiles from the selected ROIs. The second component, the hard attention classification model further extracts a sequence of multi-resolution glimpses from each tile for classification. Since hard attention is non-differentiable, we train this component using reinforcement learning to predict the location of the glimpses. This approach allows the model to focus on essential regions instead of processing the entire tile, thereby aligning with a pathologist's way of diagnosis. The two components are trained in an end-to-end fashion using a joint loss function to demonstrate the efficacy of the model. The proposed model was evaluated on two WSI-level classification problems: Human epidermal growth factor receptor 2 (HER2) scoring on breast cancer histology images and prediction of Intact/Loss status of two Mismatch Repair (MMR) biomarkers from colorectal cancer histology images. We show that the proposed model achieves performance better than or comparable to the state-of-the-art methods while processing less than 10% of the WSI at the highest magnification and reducing the time required to infer the WSI-level label by more than 75%. The code is available at github.

Implementation of HER2 Testing in Endometrial Cancer, a Summary of Real-World Initial Experience in a Large Tertiary Cancer Center

HER2-targeted therapies have transformed the management of advanced or recurrent serous endometrial cancer (EC), leading to an increased clinical demand for HER2 testing. Despite its adoption in select academic centers, the global extent of such tumor testing is unclear. In this study, we report on the initial two-year experience of HER2 testing at a major academic center with a reference gynecologic oncology service and biomarker reference laboratory. All patients who underwent HER2 testing based on physician discretion, reflex HER2 testing, and reference laboratory requests were included. From February 2021 to October 2023, HER2 testing was performed on 192 tumor tissue samples from 180 EC patients. Serous carcinoma constituted 52% of samples, reflecting diagnostic challenges and limited therapeutic options for advanced EC. HER2 positivity was found in 28% of all cases and 30% of p53-aberrant cases. An immunohistochemistry (IHC) score of 3+ was found in 15% of samples, while IHC 2+ was found in 45% (13% IHC 2+/ISH+ and 32% IHC 2+/ISH-). The newly identified 'HER2-low' category comprised 46% of the samples. Heterogeneity was noted in 42% of HER2-positive cases, with complex patterns in 3%. NGS and HER2 IHC-FISH showed a 24% discordance, attributed to intratumoral heterogeneity, tumor cellularity, a small number of amplified cells, and the HER2/CEP17 ratio near the cut-off. This study offers real-world insights into HER2 testing in EC, highlighting the challenges and underscoring the need for standardized guidelines in specimen handling, proficiency testing, and scoring criteria to enhance patient management and therapeutic decision-making.

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.

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.

Unlocking the Resistance to Anti-HER2 Treatments in Breast Cancer: The Issue of HER2 Spatial Distribution

Approximately 15% of breast cancers are classified as HER2-positive, with an amplification of the ERBB2 gene and/or an overexpression of the HER2 protein. Up to 30% of HER2-positive breast cancers shows heterogeneity in HER2 expression and different patterns of spatial distribution, i.e., the variability in the distribution and expression of the HER2 protein within a single tumour. Spatial heterogeneity may potentially affect treatment, response, assessment of HER2 status and consequently, may impact on the best treatment strategy. Understanding this feature can help clinicians to predict response to HER2-targeted therapies and patient outcomes, and to fine tune treatment decisions. This review summarizes the available evidence on HER2 heterogeneity and spatial distribution and how this may affect current available treatment choices, exploring possible opportunities for overcoming this issue, such as novel pharmacological agents, belonging to the group of antibody-drug conjugates.

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.

Equivocal (HER2 IHC 2+) breast carcinomas: gene-protein assay testing reveals association between genetic heterogeneity, individual cell amplification status and potential treatment benefits

AIMS

Genetic heterogeneity can pose a challenge to identifying eligible cases for targeted therapy in the human epidermal growth factor receptor 2 (HER2) immunohistochemistry (IHC) 2+ breast carcinoma group. In this study, we characterised this subset of tumours according to clinicopathological parameters.

METHODS AND RESULTS

We assessed 1000 tumour cells per case and recorded the number of HER2 and chromosome enumeration probe 17 (CEP17) copies using gene-protein assay slides. HER2 status was determined based on ASCO/CAP 2013 guidelines. Tumours with 5-50% of cancer cells with amplification were considered to be heterogeneous, whereas those with >50% were considered to be non-heterogeneous. In a study cohort of 110 HER2 IHC 2+ carcinomas, 93 (84.5%) were non-amplified, 12 (10.9%) were amplified and five (4.5%) were ISH-equivocal. All the HER2-amplified and two of ISH-equivocal cases (12.7%) corresponded to non-heterogeneous tumours, with highly significant differences evident in the average HER2/CEP17 ratio (P = 0.0002) and the proportion of cells with HER2 >6 copies (P < 0.0001) compared with heterogeneous lesions. NST grade 3 and HER2-amplified carcinomas average HER2/CEP17 ratio correlated with an increased number of cells with HER2/CEP17 ≥2.0 (P < 0.014). Triple-negative CEP17 polysomic carcinomas showed increased metastatic capacity (P = 0.003) compared with other tumour types.

CONCLUSION

Non-heterogeneous HER2 IHC 2+ tumours tend to be HER2-amplified. Adding the percentage of cells with HER2 >6 copies to the average HER2/CEP17 ratio may facilitate assessment of amplification status in ISH-equivocal cases. The proportion of cells with HER2/CEP17 ≥2.0 contributes information concerning the actual average HER2/CEP17 ratio, depending on tumour type.

Automated Image Analysis of HER2 Fluorescence In Situ Hybridization to Refine Definitions of Genetic Heterogeneity in Breast Cancer Tissue

Human epidermal growth factor receptor 2 gene- (HER2-) targeted therapy for breast cancer relies primarily on HER2 overexpression established by immunohistochemistry (IHC) with borderline cases being further tested for amplification by fluorescence in situ hybridization (FISH). Manual interpretation of HER2 FISH is based on a limited number of cells and rather complex definitions of equivocal, polysomic, and genetically heterogeneous (GH) cases. Image analysis (IA) can extract high-capacity data and potentially improve HER2 testing in borderline cases. We investigated statistically derived indicators of HER2 heterogeneity in HER2 FISH data obtained by automated IA of 50 IHC borderline (2+) cases of invasive ductal breast carcinoma. Overall, IA significantly underestimated the conventional HER2, CEP17 counts, and HER2/CEP17 ratio; however, it collected more amplified cells in some cases below the lower limit of GH definition by manual procedure. Indicators for amplification, polysomy, and bimodality were extracted by factor analysis and allowed clustering of the tumors into amplified, nonamplified, and equivocal/polysomy categories. The bimodality indicator provided independent cell diversity characteristics for all clusters. Tumors classified as bimodal only partially coincided with the conventional GH heterogeneity category. We conclude that automated high-capacity nonselective tumor cell assay can generate evidence-based HER2 intratumor heterogeneity indicators to refine GH definitions.

Utility of cytopathological specimens and an automated image analysis for the evaluation of HER2 status and intratumor heterogeneity in breast carcinoma

OBJECTIVES

Although updated HER2 testing guidelines have been improved by a collaboration between the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) in 2013, HER2 evaluation is still problematic because of issues involving CEP17 polysomy, heterogeneity, and HER2 score 2+ cases. The aim of this retrospective study was to evaluate the relationship between HER2 gene heterogeneity, or so called CEP17 polysomy, using breast carcinoma cells sampled by scraping and the IHC score graded by automated image analysis using whole slide image.

MATERIAL AND METHODS

We randomly selected 23 breast carcinoma cases with a HER2 score 0, 24 cases with a HER2 score 1+, 24 cases with HER2 score 2+, and 23 cases with HER2 score 3+ from the records of patients with breast cancer at Hiroshima University Hospital. We compared the results of fluorescent in situ hybridization (FISH) using formalin-fixed, paraffin-embedded (FFPE) tissues and cytological samples and compared the HER2 score calculated using an automated image analysis using wholly scanned slide images and visual counting.

RESULTS

We successfully performed the FISH assay in 78 of 94 cases (83%) using FFPE tissues and in all 94 (100%) cases using cytological samples. Frequency of both HER2 amplification and CEP17 polysomy was higher when cytological samples were used than when FFPE tissue was used. Frequency of HER2 heterogeneity using cytological samples was higher that than using FFPE tissue, except for the IHC score 3+ cases.

CONCLUSIONS

When assessment of HER2 status based on FISH using FFPE tissue cannot be accomplished, FISH using cytological samples should be considered. When intensity of HER2 is heterogeneous in the tumor tissue, particularly in cases regarded as score 2+, they should be evaluated by automated image analysis using the whole slide image.

[Immunohistochemical changes in the lungs from fetuses and newborn infants at 20- 40 weeks' gestation with false left-sided congenital diaphragmatic hernia]

OBJECTIVE

to study changes in the expression of growth factors in the lungs from fetuses and newborn infants at 20-40 weeks' gestation with false left-sided congenital diaphragmatic hernia (CDH).

MATERIAL AND METHODS

Lung fragments obtained at autopsies were examined using immunohistochemically stained paraffin sections. The expression indices of insulin-like growth factor-1 (IGF-1), platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and transforming grow factor-β (TGF-β) in the fetal lung sections were compared with the results of survey and elective staining techniques, the morphometric data of digitized lung sections, and the indicators obtained in the comparison group.

RESULTS

Morphofunctional changes in the connective tissue, pulmonary vessels, and bronchial and alveolar epithelium at 20-24, 25-27, and 28-40 weeks' gestation were characterized, partly explaining the development of bilateral pulmonary hypoplasia in CDH. There was evidence for the involvement of PDGF, IGF-1, and EGF in primary pulmonary hypoplasia. PDGF deficiency plays a certain role in secondary pulmonary hypoplasia.

CONCLUSION

The findings can be used in researches and in the practical work of pathologists and forensic medical experts.

Clinicopathologic Significance of the Intratumoral Heterogeneity of HER2 Gene Amplification in HER2-Positive Breast Cancer Patients Treated With Adjuvant Trastuzumab

OBJECTIVES

Although intratumoral heterogeneity of human epidermal growth factor receptor 2 (HER2) gene amplification has been associated with a poor prognosis for primary HER2-positive breast cancer and metastatic HER2-positive breast cancer treated with trastuzumab, the clinicopathologic significance in a setting involving trastuzumab treatment as an adjuvant treatment has not been studied in patients.

METHODS

We retrospectively investigated 443 patients with HER2-positive breast cancer treated with surgery, adjuvant chemotherapy, and 1 year of trastuzumab. Three areas that showed different levels of HER2 protein expression were chosen, and silver in situ hybridization was performed.

RESULTS

HER2 regional and genetic heterogeneity was found in 6.2% and 6.8% of tumors, respectively. Both types of heterogeneity were significantly associated with hormone receptor positivity, HER2 immunohistochemistry score of 2+, a low level of HER2 gene amplification, and absence of an extensive intraductal component. Genetic heterogeneity also showed strong correlation with a lower histologic grade. In the hormone receptor-positive group, the regional heterogeneity affected disease-free survival of patients (hazard ratio, 4.869; 95% confidence interval, 1.424-16.646; P = .005), whereas genetic heterogeneity did not.

CONCLUSIONS

Evaluation of intratumoral heterogeneity, especially in cases with hormone receptor positivity, may be valuable for assessing the prognosis of HER2-positive patients anticipating treatment with adjuvant systemic therapy and trastuzumab.

Detecting intratumoral heterogeneity in routine breast-HER2 testing: low yield of testing multiple blocks

BACKGROUND

Intratumoral heterogeneity can lead to uncertainty in breast carcinoma HER2 testing, both with respect to pathology reporting and clinical significance. The standard practice is to perform breast biomarker testing on a single representative section of tumor; however, concern over heterogeneity often leads to testing on additional tissue blocks. Our objective was to assess the diagnostic yield of testing multiple blocks of a single invasive breast carcinoma.

METHODS

We performed a retrospective review of 139 consecutive cases (between 2006 and 2012) in which clinical HER2 testing was performed in multiple blocks. Tumor characteristics and HER2 studies (both immunohistochemistry and data from in situ hybridization) were reviewed. Regional differences in morphology and HER2 immunoreactivity were recorded. In situ hybridization was performed in 25 of 139 of the cases; patterns of genetic heterogeneity were reviewed. We audited discordances in HER2 result between blocks.

RESULTS

Testing of multiple blocks yielded no additional HER2 information in 134 (96.4%) of 139 cases. Morphologic differences or heterogeneity in HER2 expression was observed in 22 (15.8%) of 139 of cases. Only 5 of these showed differences in HER2 between blocks, of which 4 were associated with equivocal HER2 immunohistochemistry, and 4 were high-grade.

CONCLUSIONS

In the vast majority of cases, even those with heterogeneity, testing of a single block is sufficient for an accurate HER2 determination. High-grade tumors with equivocal HER2 status and observable heterogeneity are more likely to yield a different result on testing of additional blocks.

HER2 gene and protein expression status of breast carcinoma can be reliably tested on a single slide

Human epidermal growth factor receptor 2 (HER2) status in breast carcinomas serves as a predictor of benefit from anti-HER2 therapy. In providing clinicians with the information necessary to decide whether or not to treat with targeted therapy, it might be necessary to choose between methods assessing HER2 protein overexpression or gene amplification. A new diagnostic approach could be a combination of both tests on the same slide. If accurate and reproducible, this approach might optimize patient stratification for therapy. In this study, formalin-fixed paraffin-embedded tumor samples from 77 breast cancer patients were examined for HER2 by immunohistochemistry (IHC) and silver in situ hybridization (SISH) using HER2 IHC (clone 4B5), HER2/CEN17SISH, and combined IHC and SISH assay, called gene protein (GP). Cases were selected to ensure a sufficient number of borderline cases on the basis of IHC scores (0, 1+, 2+, 3+), obtained during diagnostic histopathological workup. The concordance between the HER2 IHC score obtained during diagnostic histopathological workup and GP was 93 %. Discordances had no influence on therapy decisions. The concordance between ISH results using dual ISH (DISH) and GP was 96 %. Of the 77 cases studied by GP, three cases with a ratio close to 2 would have been called amplified by DISH. The use of GP reduced the time for slide reading for a trained pathologist by up to 25 %, relative to sequential reading of IHC followed by SISH. For cases with an IHC score of 2+, the final result was obtained in 1 day, while the sequential technique would have required retesting by ISH on a second day. In conclusion, assessment of HER2 status by GP is an improvement for pathologists and facilitates clinical decision-making for breast cancer management.

[Use of the new 2013 ASCO/CAP guidelines to study HERS status by fluorescence in situ hybridization in patients with breast cancer]

Despite the long-term history of HER2 testing in breast cancer (BC), the results of its study are frequently interpreted ambiguously. The introduction of the new 2013 ASCO/CAP guidelines is aimed to further optimize HERS testing in view of new scientific evidence for the biological characteristics of BC.

OBJECTIVE

to study the results of assessing HERS2 status in patients with the questionable level of protein expression according to the 2007 versus 2013 ASCO/CAP criteria.

SUBJECTS AND METHODS

Biopsy specimens from 572 patients diagnosed with BC after immunohistochemical examination, including HER2 status assessment, were investigated by fluorescence in situ hybridization.

RESULTS

The use of the new 2013 ASCO/CAP criteria versus the previous criteria to determine intratumor heterogeneity, HER2 gene copy number, and the so-called chromosome 17 polysomy was ascertained to cause a statistically significant increase in HER2-positive cases from 25 to 42.5% (OR=2.2178; 95% CI, 1.8254-2.6950; р=0.0005).

CONCLUSION

The use of the new guidelines additionally permits effective therapy in patients with BC, which may be another step to improve survival in this large patient group.

Problems In Determining Her2 Status In Breast Carcinoma

OBJECTIVE

Human epidermal growth factor receptor 2 (HER2) oncoprotein is overexpressed in 15-25% of breast carcinomas and associated with poor outcome. Assessment of HER2 status accurately is important to select patients who will benefit from targeted therapy.

MATERIALS AND METHODS

In this study immunohistochemistry (IHC) and fluorescence in situ hybridization (FISH) were used to determine the HER2 status in 308 breast carcinoma cases of which 129 were consultation. The major problems in determining HER2 status and the reasons of discordant results between methods were discussed.

RESULTS

HER2 expression was (-) in 124, (+) in 29, (++) in 92, (+++) in 63 cases. 25 of 76 cases consulted as (++) were evaluated as (++) and 15 of 35 cases consulted as (+++) were evaluated as (+++). HER2 amplification was found in 88 (28.6%) of 308 cases by FISH. 3 of 124 (-), 1 of 29 (+), 22 of 92 (++), 62 of 63 (+++) cases were amplified by FISH. The relation between HER2 expression and amplification was statistically significant (p<0.001). Centromere 17 (CEN 17) region amplification was noted in 11 cases of which 2 were (+++), 9 were (++). 6 of the 11 cases showed focal low level, 1 of them showed diffuse high level amplification.

CONCLUSION

The concordance rate between IHC (+++) cases and FISH was 95.4% for consultation cases, 100% for our cases. The final concordance rate for both case groups was 98.4%. The possible reasons of discrepancy were triple negativity, preanalytical and analytical procedures of consultation cases and trucut samples.

HER2 heterogeneity affects trastuzumab responses and survival in patients with HER2-positive metastatic breast cancer

OBJECTIVES

Heterogeneity of HER2 gene amplification is found in a subset of breast cancers. We investigated the impact of HER2 heterogeneity on trastuzumab responses and clinical outcomes in 112 patients with HER2-positive metastatic breast cancer.

METHODS

Regional and genetic heterogeneity of HER2 gene amplification was determined in three different areas of each tumor by immunohistochemistry and silver in situ hybridization. We also assessed the overall levels of HER2 amplification and the proportion of tumor cells with a HER2/CEP17 ratio of more than 2.2 or strong and complete membranous (3+) expression of HER2 protein.

RESULTS

HER2 regional and genetic heterogeneity based on the HER2/CEP17 ratio was confirmed in 8.7% and 2.7% of cases, respectively. Poor response to trastuzumab was associated with overall low-level or equivocal amplification, HER2 regional heterogeneity by the HER2/CEP17 ratio, the HER2/CEP17 ratio of more than 2.2 in less than 80% of tumor cells, and HER2 immunohistochemical expression of 3+ in less than 75% of tumor cells. In survival analyses, low-level or equivocal HER2 amplification, HER2 regional heterogeneity based on the HER2/CEP17 ratio, and the HER2/CEP17 ratio of more than 2.2 in less than 80% of tumor cells were associated with shorter time to progression and lower overall survival in univariate and multivariate analyses.

CONCLUSIONS

These results suggest that accurate assessment of HER2 status, including HER2 heterogeneity, is important in predicting trastuzumab responses and outcomes in patients with HER2-positive metastatic breast cancer.

FISH molecular testing in cytological preparations from solid tumors

Many of the exciting new developments in solid tumor molecular cytogenetics impact classical and molecular pathology. Fluorescence in situ hybridization to identify specific DNA target sequences in nuclei of non-dividing cells in solid neoplasms has contributed to the integration of molecular cytogenetics into cytology in spite of the remarkable promiscuity of cancer genes. Indeed, although it is a low-throughput assay, fluorescence in situ hybridization enables the direct disclosure and localization of genetic markers in single nuclei. Gene fusions are among the most prominent genetic alterations in cancer, providing markers that may be determinant in needle biopsies that are negative or suspicious for malignancy, and may contribute to the correct classification of the tumors. In view of the expanding use of fluorescence in situ hybridization in cytology, future challenges include automated sample evaluation and the specification of common criteria for interpreting and reporting results.

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

Trastuzumab-containing therapy is a standard of care for patients with HER2+ breast cancer. HER2 status is routinely assigned using in situ hybridization to assess HER2 gene amplification, but interpretation of in situ hybridization results may be challenging in tumors with chromosome 17 polysomy or intratumoral genetic heterogeneity. Apparent chromosome 17 polysomy, defined by increased chromosome enumeration probe 17 (CEP17) signal number, is a common genetic aberration in breast cancer and represents an alternative mechanism for increasing HER2 copy number. Some studies have linked elevated CEP17 count ('polysomy') with adverse clinicopathologic features and HER2 overexpression, although there are numerous discrepancies in the literature. There is evidence that elevated CEP17 ('polysomy') count might account for trastuzumab response in tumors with normal HER2:CEP17 ratios. Nonetheless, recent studies establish that apparent 'polysomy' (CEP17 increase) is usually related to focal pericentromeric gains rather than true polysomy. Assigning HER2 status may also be complex where multiple cell subclones with distinct HER2 amplification characteristics coexist within the same tumor. Such genetic heterogeneity affects up to 40% of breast cancers when assessed according to a College of American Pathologists guideline, although other definitions have been proposed. Recent data have associated heterogeneity with unfavorable clinicopathologic variables and poor prognosis. Genetically heterogeneous tumors harboring HER2-amplified subclones have the potential to benefit from trastuzumab, but this has yet to be evaluated in clinical studies. In this review, we discuss the implications of apparent polysomy 17 and genetic heterogeneity for assigning HER2 status in clinical practice. Among our recommendations, we support the use of mean HER2 copy number rather than HER2:CEP17 ratio to define HER2 positivity in cases where coamplification of the centromere might mask HER2 amplification. We also highlight a need to harmonize in situ hybridization scoring methodology to support accurate HER2 status determination, particularly where there is evidence of heterogeneity.

ESR1 amplification in breast cancer by optimized RNase FISH: frequent but low-level and heterogeneous

Prevalence of ESR1 amplification in breast cancer is highly disputed and discrepancies have been related to different technical protocols and different scoring approaches. In addition, pre-mRNA artifacts have been proposed to influence outcome of ESR1 FISH analysis. We analyzed ESR1 gene copy number status combining an improved RNase FISH protocol with multiplex ligation-dependent probe amplification (MLPA) after laser microdissection. FISH showed a high prevalence of ESR1 gains and amplifications despite RNase treatment but MLPA did not confirm ESR1 copy number increases detected by FISH in more than half of cases. We suggest that the combination of the ESR1-specific intra-tumor heterogeneity and low-level copy number increase accounts for these discrepancies.

Concordance of ATM (ataxia telangiectasia mutated) immunohistochemistry between biopsy or metastatic tumor samples and primary tumors in gastric cancer patients

ATM (ataxia telangiectasia mutated) is one of several DNA repair proteins that are suggested to sensitize tumor cells to the poly(ADP-ribose) polymerase inhibitor olaparib when deficient. The aim of this study was to assess the spatiotemporal concordance of ATM immunohistochemistry (IHC) in gastric cancer in order to determine if measurements made at the level of various sample types and times could be inferred as having the potential to be relevant to treatment decisions made at the patient level. Two independent cohorts composed of 591 gastric cancer patients divided into a gastrectomy cohort (n = 450) and a metastasis cohort (n = 141) were used in this study. A total of 2,705 ATM IHC samples were examined, including 450 whole tissue, 3 sets of 450 tissue microarray (TMA), 301 biopsy, 222 metastatic tumor and 2 additional whole tissue samples of 50 cases from the gastrectomy cohort, and 141 pairs of primary and metastatic tumors from the metastasis cohort. The prevalence of ATM negativity was 13.1% in biopsies, 13.9, 15.1, and 16.0% in TMAs and 15.9% in whole tissue samples of the gastrectomy cohort, and 21.4% in primary tumor and 21.5% in metastatic tumor samples of the metastasis cohort. coefficients were 0.341 for biopsy, 0.572 as the average of 3 TMAs and 0.415 for the largely synchronous metastatic tumors of the gastrectomy cohort, and 0.153 for the largely asynchronous metastatic tumors of the metastasis cohort. Using whole tissue sections from tumor resections or primary tumor, respectively, as the reference standards, specificity and sensitivity were 91.6 and 41.0% for biopsy, 93.9 and 61.9% as the average of 3 TMAs, and 86.6 and 58.8% for metastatic tumors of the gastrectomy cohort and 81.7 and 33.3% for metastatic tumors of the metastasis cohort, respectively. Although we have demonstrated that the IHC assay for ATM was robust and reproducible in gastric tumor samples, we have also found that measurements were subject to significant discordance across multiple sample types from the same patient. Further work will be necessary to determine if classification may be made more consistent by multiple sampling. However, the lack of agreement between primary and asynchronous metastatic samples suggests that such sampling would need to be performed at the time of any treatment decision.

Molecular pathology of breast cancer: what a pathologist needs to know

Pathologists are now more than ever "diagnostic oncologists" and serve a critical role as clinical consultants on the biology of disease. In the last decade and a half, molecular information has transformed our thinking about the biologic diversity of breast cancers and redirected the way clinical treatment decisions are made. A basic understanding of the current molecular classification of breast cancers and the biologic pathways from precursors to invasive disease is key to both informing diagnostic practice and serving as clinical consultants. In addition, both single-marker and panel-based molecular tests are currently being utilized in breast cancer tissue to predict the benefit of specific therapies such as HER2-targeted biologic therapy and chemotherapy. Familiarity with the current issues involving these molecular tests as well as the pathologist's role in ensuring appropriate tissue handling, tissue selection, and results interpretation and correlation are paramount to providing optimal patient care.

A gene-protein assay for human epidermal growth factor receptor 2 (HER2): brightfield tricolor visualization of HER2 protein, the HER2 gene, and chromosome 17 centromere (CEN17) in formalin-fixed, paraffin-embedded breast cancer tissue sections

BACKGROUND

The eligibility of breast cancer patients for human epidermal growth factor receptor 2 (HER2)-directed therapies is determined by the HER2 gene amplification and/or HER2 protein overexpression status of the breast tumor as determined by in situ hybridization (ISH) or immunohistochemistry (IHC), respectively. Our objective was to combine the US Food and Drug Administration (FDA)-approved HER2 & chromosome 17 centromere (CEN17) brightfield ISH (BISH) and HER2 IHC assays into a single automated HER2 gene-protein assay allowing simultaneous detection of all three targets in a single tissue section.

METHODS

The HER2 gene-protein assay was optimized using formalin-fixed, paraffin-embedded (FFPE) samples of the xenograft tumors MCF7 [HER2 negative (non-amplified gene, protein negative)] and Calu-3 [HER2 positive (amplified gene, protein positive)]. HER2 IHC was performed using a rabbit monoclonal anti-HER2 antibody (clone 4B5) and a conventional 3,3'-diaminobenzidine IHC detection. The HER2 & CEN17 BISH signals were visualized using horseradish peroxidase-based silver and alkaline phosphatase-based red detection systems, respectively with a cocktail of 2,4-dinitrophenyl-labeled HER2 and digoxigenin-labeled CEN17 probes. The performance of the gene-protein assay on tissue microarray slides containing 189 randomly selected FFPE clinical breast cancer tissue cores was compared to that of the separate HER2 IHC and HER2 & CEN17 BISH assays.

RESULTS

HER2 protein detection was optimal when the HER2 IHC protocol was used before (rather than after) the BISH protocol. The sequential use of HER2 IHC and HER2 & CEN17 BISH detection steps on FFPE xenograft tumor sections appropriately co-localized the HER2 protein, HER2 gene, and CEN17 signals after mitigating the silver background staining by using a naphthol phosphate-containing hybridization buffer for the hybridization step. The HER2 protein and HER2 gene status obtained using the multiplex HER2 gene-protein assay demonstrated high concordance with those obtained using the separate HER2 IHC and HER2 & CEN17 BISH assays, respectively.

CONCLUSIONS

We have developed a protocol that allows simultaneous visualization of the HER2 IHC and HER2 & CEN17 BISH targets. This automated protocol facilitated the determination of HER2 protein and HER2 gene status in randomly selected breast cancer samples, particularly in cases that were equivocal or exhibited tumor heterogeneity. The HER2 gene-protein assay produced results virtually equivalent to those of the single FDA-approved HER2 IHC and HER2 & CEN17 BISH assays.

VIRTUAL SLIDES

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/2041964038705297.