Quantitation of HER2 expression or HER2:HER2 dimers and differential survival in a cohort of metastatic breast cancer patients carefully selected for trastuzumab treatment primarily by FISH

EGFR-directed antibodies promote HER2 ADC internalization and efficacy

Trastuzumab deruxtecan (T-DXd) is a human epidermal growth factor receptor 2 (HER2)-targeting antibody drug conjugate that has remarkable activity in HER2-positive cancers. However, the degree of benefit of T-DXd is not uniform among solid tumors even with high levels of HER2. Despite high HER2 expression, the HER2/T-DXd complex may not always undergo internalization and payload release dependent on the receptor's conformation and context. We hypothesize that epidermal growth factor receptor (EGFR), a dimerization partner of HER2, can modulate HER2 trafficking through endocytic pathways and affect T-DXd uptake. We demonstrate that elevated EGFR expression levels can promote EGFR/HER2 heterodimer formation and suppress T-DXd internalization and efficacy. Knockdown of EGFR expression or pharmacologic stimulation of EGFR endocytosis with EGFR monoclonal antibodies restores T-DXd trafficking and antitumor activity in EGFR-overexpressing cancers in vivo. Our results reveal EGFR overexpression to be a potential mechanism of resistance to T-DXd, which can be overcome by combination therapy strategies targeting EGFR.

Quantification of HER1, HER2 and HER3 by time-resolved Förster resonance energy transfer in FFPE triple-negative breast cancer samples

Background

Triple-negative breast cancer (TNBC) has a worse prognosis compared with other breast cancer subtypes, and biomarkers to identify patients at high risk of recurrence are needed. Here, we investigated the expression of human epidermal receptor (HER) family members in TNBC and evaluated their potential as biomarkers of recurrence.

Methods

We developed Time Resolved-Förster Resonance Energy Transfer (TR-FRET) assays to quantify HER1, HER2 and HER3 in formalin-fixed paraffin-embedded (FFPE) tumour tissues. After assessing the performance and precision of our assays, we quantified HER protein expression in 51 TNBC specimens, and investigated the association of their expression with relapse-free survival.

Results

The assays were quantitative, accurate, and robust. In TNBC specimens, HER1 levels ranged from ≈4000 to more than 2 million receptors per cell, whereas HER2 levels varied from ≈1000 to 60,000 receptors per cell. HER3 expression was very low (less than 5500 receptors per cell in all samples). Moderate HER2 expression was significantly associated with higher risk of recurrence (HR = 3.93; P = 0.003).

Conclusions

Our TR-FRET assays accurately quantify HER1, HER2 and HER3 in FFPE breast tumour specimens. Moderate HER2 expression may represent a novel prognostic marker in patients with TNBC.

HER2 amplification level is not a prognostic factor for HER2-positive breast cancer with trastuzumab-based adjuvant treatment: a systematic review and meta-analysis

Background

Trastuzumab-based therapy is a standard, targeted treatment for HER2-positive breast cancer in the adjuvant setting. However, patients do not benefit equally from it and the association between HER2 amplification level and patients' survival remains controversial. A systematic review and meta-analysis was conducted by incorporating all available evidence to evaluate the association between disease free survival (DFS) and HER2 amplification level.

Results

Three cohort studies involving 1360 HER2-positive breast cancer patients stratified by HER2 amplification magnitude were eligible for meta-analysis. The combined HRs for DFS were 1.05 (95% CI: 0.80−1.36, p = 0.74) and 0.97 (95% CI: 0.73−1.29, p = 0.83) for HER2 gene copy number (GCN) and HER2/CEP 17 ratio. No evidence of heterogeneity or public bias was found.

Methods

Databases including PubMed, Embase, Web of Science, and Cochrane Central Register of Controlled Trials (CENTRAL), were searched for eligible literature. HER2 amplification level was evaluated by fluorescence in situ hybridization (FISH) in terms of gene copy number (GCN) and HER2/CEP17 ratio. Hazard ratios (HRs) for DFS with 95% confidence interval (CI) according to the amplification level of HER2 were extracted. The outcomes were synthesized based on a fixed-effects model.

Conclusions

HER2 amplification level is not a prognostic factor for HER2-positive breast cancer with trastuzumab-based targeted therapy in the clinical adjuvant setting.

Well-differentiated invasive breast cancers with equivocal HER2 immunohistochemistry: what is the yield of routine reflex in-situ hybridization testing?

AIMS

The 2013 American Society of Clinical Oncology and the College of American Pathologists (ASCO/CAP) HER2 guidelines recommend testing all invasive breast cancers for HER2, typically with immunohistochemistry (IHC) followed by in-situ hybridization (ISH) when IHC is equivocal. As well-differentiated breast cancers are rarely HER2-positive, we assessed the value of routine reflex HER2 ISH testing for this subset of breast cancers.

METHODS AND RESULTS

We collected HER2 IHC 2+ cases and fluorescence in-situ hybridization (FISH) data from primary breast cancers with well-differentiated tumour types (grade 1 ductal carcinomas, classic lobular carcinomas, tubular, cribriform and pure mucinous carcinomas) at our centre from 2010 to 2015. Haematoxylin and eosin (H&E) and IHC slides were reviewed to confirm tumour type, grade and IHC score based on ASCO/CAP 2013 guidelines and their recent revisions. Of 4633 invasive carcinomas, 1133 had a well-differentiated tumour type; 177 of these were HER2 IHC equivocal, three of which were low-level amplified by FISH (0.3% of all well-differentiated tumours). One amplified case was classic invasive lobular carcinoma and two were invasive ductal carcinomas, grade 1. One amplified case had chromosome 17 monosomy, and one was rescored as HER2 IHC 1+ upon review. 'Basolateral' staining was noted in one amplified case and in 65 of 174 (37.4%) non-amplified cases. This incomplete membranous staining pattern was observed in the majority of invasive ductal carcinomas that were rescored as 1+ according to the revised 2013 guidelines.

CONCLUSIONS

The rate of HER2 amplification among well-differentiated breast cancers is very low. Basolateral staining in well-differentiated tumours may be overinterpreted as HER2 IHC 2+, but is rarely associated with HER2 amplification.

Local variations of HER2 dimerization in breast cancer cells discovered by correlative fluorescence and liquid electron microscopy

The formation of HER2 homodimers plays an important role in breast cancer aggressiveness and progression; however, little is known about its localization. We have studied the intra- and intercellular variation of HER2 at the single-molecule level in intact SKBR3 breast cancer cells. Whole cells were visualized in hydrated state with correlative fluorescence microscopy and environmental scanning electron microscopy (ESEM). The locations of individual HER2 receptors were detected using an anti-HER2 affibody in combination with a quantum dot (QD), a fluorescent nanoparticle. Fluorescence microscopy revealed considerable differences of HER2 membrane expression between individual cells and between different membrane regions of the same cell (that is, membrane ruffles and flat areas). Subsequent ESEM of the corresponding cellular regions provided images of individually labeled HER2 receptors. The high spatial resolution of 3 nm and the close proximity between the QD and the receptor allowed quantifying the stoichiometry of HER2 complexes, distinguishing between monomers, dimers, and higher-order clusters. Downstream data analysis based on calculating the pair correlation function from receptor positions showed that cellular regions exhibiting membrane ruffles contained a substantial fraction of HER2 in homodimeric state. Larger-order clusters were also present. Membrane areas with homogeneous membrane topography, on the contrary, displayed HER2 in random distribution. Second, HER2 homodimers appeared to be absent from a small subpopulation of cells exhibiting a flat membrane topography, possibly resting cells. Local differences in homodimer presence may point toward functional differences with possible relevance for studying metastasis and drug response.

Prognostıc value of increased HER2 expression in cancers of pancreas and biliary tree

Increased HER2 expression has a prognostic, and predictive value in many solid cancer types, predominantly in breast cancer. However the effects of HER2 on survival from cancers of pancreas, gall bladder, cholangiocellular, and ampullary region are not known. In this study, the effects of increased HER2 expression on these types of cancer have been analyzed. Immunohistochemical HER2 staining was performed in 31 (44.9 %) female, and 38 (55.1 %) male patients with a mean age of 65 ± 10 years, and various parameters, mostly survival rates of patients with pancreas (n = 30; 43.5 %), gall bladder (n = 17; 24.6 %), cholangiocellular (n = 12; 17.4 %), and ampullary region (n = 10; 14.5 %) carcinomas were evaluated. Strong (3 +) membranous staining for HER2 was observed in 2 patients with gall bladder cancers (11.76 % of all gall bladder cancers). In 2.90 % of all cases strong membranous staining (2+ or 3+) was observed. Weak (1+) membranous staining was noted in one (3.33 %) pancreatic, and one cholangiocellular (8.33 %) cancer patient, and in none of the ampullary region patient membranous staining for HER2 was observed. Since only scarce number of patients demonstrated membranous staining for HER2, survival analysis was not performed on these patients. Based on cytoplasmic HER2 staining scores, the patients were divided into weakly (0-3 pts; n = 17 patients; 24.66 %), moderate (4-5 pts; n = 22; 31.88 %), and strongly (6-7 pts; n = 30; 43.46 %) stained groups. Patients whose specimens demonstrated borderline statistical significant (p = 0.052) low staining for HER2 had higher survival rates when compared with other cases. Increased HER2 expression has no prognostic, and predictive value in cancers of pancreas, biliary tract, and ampulla vateri. If HER2 will be evaluated in these types of cancer, membranous, as well as cytoplasmic staining properties should be taken into account.

Proximity probing assays for simultaneous visualization of protein complexes in situ

EVALUATION OF: Leuchowius KJ, Clausson CM, Grannas K et al. Parallel visualization of multiple protein complexes in individual cells in tumor tissue. Mol. Cell Proteomics doi:10.1074/mcp.O112.023374 (2013) (Epub ahead of print). Techniques for in situ detection and quantification of proteins in fixed tissue remain an important element of both basic biological analyses and clinical biomarker research. The practical importance of such techniques can be exemplified by the everyday clinical use of immunohistochemical detection of the estrogen receptor and HER2 in tissues from breast cancer patients. Several techniques are currently available for detection of single proteins and post-translational modifications, but very few are suitable for detection of protein complexes. Methods that enable simultaneous detection and quantification of protein complexes provide novel possibilities for understanding the biological role(s) of protein complexes and may open new opportunities to improve clinical biomarker research. Leuchowius et al. describe an improved proximity ligation assay for in situ detection of protein complexes, which is able to detect and quantify several protein complexes simultaneously in the same tissue specimen.

High-level ERBB2 gene amplification is associated with a particularly short time-to-metastasis, but results in a high rate of complete response once trastuzumab-based therapy is offered in the metastatic setting

Despite patient selection based on ERBB2 overexpression, not all patients benefit from trastuzumab therapy. We have investigated whether a ERBB2 gene dosage effect might provoke increased biological aggressiveness and altered trastuzumab sensitivity. Absolute ERBB2 copy numbers ("CN") and ERBB2/centromer 17 ratios ("R") were measured by FISH analysis in tumors of 127 patients receiving trastuzumab-based treatment for Her-2/neu overexpressing metastatic breast cancer. CN and R were both significantly associated with shorter time to first metastasis (TTM) (CN: OR: 1.099, 95% CI: 1.042-1.159; R: OR: 1.211, 95% CI: 1.080-1.357) and longer PFS (CN: OR: 0.917, 95% CI: 0.867-0.969; R: OR: 0.840, 95% CI: 0.743-0.949) in a continuous variable Cox's regression model. Tumors with ERBB2/centromer 17 ratios of <2.2 had a significantly shorter TTM (p = 0.002) and significantly longer PFS (p = 0.003) than tumors with low-level (R: 2.2-6) and high-level amplification (R: >6). Interestingly, when ERBB2 copy numbers were analyzed, a significantly shorter TTM (p = 0.001) and longer PFS (p = 0.026) were observed in the group with high-level amplified CN (CN: >13), while no difference was observed between non- and low-level amplified CN. R, but not CN, was an independent predictor of complete (CR; OR: 1.685; 95% CI: 1.122-2.532) and partial (PR; OR: 1.704; 95% CI: 1.136-2.556) response in logistic regression analysis. CR (p = 0.016) rates were significantly higher in the high-level amplification group (R > 6), but no difference existed in response rates between non- and low-level amplified tumors in Chi-square tests. High-level ERBB2 amplification is associated with shorter TTM, but improved response to trastuzumab in metastatic breast cancer.

Parallel visualization of multiple protein complexes in individual cells in tumor tissue

Cellular functions are regulated and executed by complex protein interaction networks. Accordingly, it is essential to understand the interplay between proteins in determining the activity status of signaling cascades. New methods are therefore required to provide information on different protein interaction events at the single cell level in heterogeneous cell populations such as in tissue sections. Here, we describe a multiplex proximity ligation assay for simultaneous visualization of multiple protein complexes in situ. The assay is an enhancement of the original proximity ligation assay, and it is based on using proximity probes labeled with unique tag sequences that can be used to read out which probes, from a pool of probes, have bound a certain protein complex. Using this approach, it is possible to gain information on the constituents of different protein complexes, the subcellular location of the complexes, and how the balance between different complex constituents can change between normal and malignant cells, for example. As a proof of concept, we used the assay to simultaneously visualize multiple protein complexes involving EGFR, HER2, and HER3 homo- and heterodimers on a single-cell level in breast cancer tissue sections. The ability to study several protein complex formations concurrently at single cell resolution could be of great potential for a systems understanding, paving the way for improved disease diagnostics and possibilities for drug development.

Pertuzumab: new hope for patients with HER2-positive breast cancer

BACKGROUND

Human epidermal growth factor receptor 2 (HER2) overexpression is detected in approximately 15% to 20% of all breast cancers (BCs). A revolutionary change in the prognosis of this subgroup of patients has occurred since trastuzumab therapy was introduced into daily clinical practice. However, because trastuzumab resistance is common, new molecules with complementary and/or synergistic mechanisms of action have been developed. Pertuzumab is a new anti-HER2 humanized monoclonal antibody that prevents the formation of HER2 dimers.

MATERIAL AND METHODS

A computer-based literature search was carried out using PubMed (keywords: breast neoplasm, dimerization, HER-2, pertuzumab); data reported at international meetings are included.

RESULTS

This paper describes pertuzumab's mechanism of action, safety, and role in HER2-positive BCs. It also explores the role of pertuzumab as a single agent or combined with trastuzumab by reviewing data from preclinical research to ongoing clinical trials. Recently published trials, particularly the CLEOPATRA study, highlight the efficacy, tolerability, and increase in disease-free survival associated with this novel agent when combined with trastuzumab.

CONCLUSION

The pertuzumab and trastuzumab anti-HER2 dual blockade is likely to represent a substantial advance for patients with HER2-positive BCs and a new milestone on the way to personalized medicine.

Testes sanguíneos de biomarcadores para diagnóstico e tratamento de desordens mentais: foco em esquizofrenia

A descoberta e a aplicação clínica de biomarcadores para desordens mentais são confrontadas com muitos desafios. Em geral, os atuais métodos de descoberta e validação de biomarcadores não produziram os resultados que foram inicialmente aguardados depois da finalização do Projeto Genoma Humano. Isso se deve principalmente à falta de processos padronizados conectando a descoberta de marcadores com tecnologias para a validação e a tradução para uma plataforma que ofereça precisão e fácil uso em clínica. Como consequência, a maior parte dos psiquiatras e praticantes em geral são relutantes em aceitar que testes de biomarcadores pode suplementar ou substituir os métodos de diagnóstico utilizados baseados em entrevista. Apesar disso, agências regulatórias concordam agora que melhoras nos correntes métodos são essenciais. Além disso, essas agências estipularam que biomarcadores são importantes para o desenvolvimento de futuras drogas e iniciaram esforços no sentido de modernizar métodos e técnicas para suportar esses esforços. Aqui revisamos os desafios encontrados por essa tentativa do ponto de vista de psiquiatras, praticantes em geral, agências reguladoras e cientistas de biomarcadores. Também descrevemos o desenvolvimento de um novo teste sanguíneo molecular para esquizofrenia como um primeiro passo a esse objetivo.

Quantification of HER expression and dimerization in patients' tumor samples using time-resolved Förster resonance energy transfer

Following the development of targeted therapies against EGFR and HER2, two members of the human epidermal receptor (HER) family of receptor tyrosine kinases, much interest has been focused on their expression in tumors. However, knowing the expression levels of individual receptors may not be sufficient to predict drug response. Here, we describe the development of antibody-based time-resolved Förster resonance energy transfer (TR-FRET) assays for the comprehensive analysis not only of EGFR and HER2 expression in tumor cryosections, but also of their activation through quantification of HER homo- or heterodimers. First, EGFR and HER2 expression levels were quantified in 18 breast tumors and the results were compared with those obtained by using reference methods. The EGFR number per cell determined by TR-FRET was significantly correlated with EGFR mRNA copy number (P<0.0001). Moreover, our method detected HER2 overexpression with 100% specificity and sensibility, as confirmed by the standard IHC, FISH and qPCR analyses. EGFR and HER2 dimerization was then assessed, using as controls xenograft tumors from cell lines with known dimer expression profiles. Our results show that quantification of HER dimerization provides information about receptor activation that cannot be obtained by quantification of single receptors. Quantifying HER expression and dimerization by TR-FRET assays might help identifying novel clinical markers for optimizing patients' treatment in oncology.

Personalized therapy for urothelial cancer: review of the clinical evidence

Despite a detailed understanding of the molecular aberrations driving the development of urothelial cancers, this knowledge has not translated into advances for the treatment of this disease. Urothelial cancers are chemosensitive, and platinum-based combination chemotherapy remains the standard of care for advanced disease, as well as neoadjuvant and adjuvant therapy for locally advanced disease. However, nearly half of patients who undergo resection of locally advanced urothelial cancer will relapse and eventually develop platinum-resistant disease. Clinical trials of targeted agents against angiogenesis and growth factors, as well as novel chemotheraputics, have generally been unsuccessful in urothelial cancers. Improvements in the theraputic arsenal for urothelial cancer depend upon identification of new targets and strategies to overcome platinum resistance.

HER2: biology, detection, and clinical implications

CONTEXT

HER2 is a membrane tyrosine kinase and oncogene that is overexpressed and gene amplified in about 20% of breast cancers. When activated it provides the cell with potent proliferative and antiapoptosis signals and it is the major driver of tumor development and progression for this subset of breast cancer. When shown to be overexpressed or amplified by appropriate methods, HER2 is a valuable treatment target.

OBJECTIVES

To review the basic biology of the HER2 signaling network, to discuss various approved methods for its detection in clinical specimens, and to describe the impressive results of therapies targeting HER2.

DATA SOURCES

Selected literature searchable on PubMed as well as older studies revealed by the literature review were reviewed.

CONCLUSION

HER2 is an important member of a complex signaling network and when gene amplified, it results in an aggressive subtype of breast cancer. Patients with tumors found to overexpress HER2 protein or to be amplified for the gene are candidates for therapy that significantly reduces mortality.

HER2: biology, detection, and clinical implications

CONTEXT

HER2 is a membrane tyrosine kinase and oncogene that is overexpressed and gene amplified in about 20% of breast cancers. When activated it provides the cell with potent proliferative and antiapoptosis signals and it is the major driver of tumor development and progression for this subset of breast cancer. When shown to be overexpressed or amplified by appropriate methods, HER2 is a valuable treatment target.

OBJECTIVES

To review the basic biology of the HER2 signaling network, to discuss various approved methods for its detection in clinical specimens, and to describe the impressive results of therapies targeting HER2.

DATA SOURCES

Selected literature searchable on PubMed as well as older studies revealed by the literature review were reviewed.

CONCLUSION

HER2 is an important member of a complex signaling network and when gene amplified, it results in an aggressive subtype of breast cancer. Patients with tumors found to overexpress HER2 protein or to be amplified for the gene are candidates for therapy that significantly reduces mortality.

Detection of hepatocyte growth factor (HGF) ligand-c-MET receptor activation in formalin-fixed paraffin embedded specimens by a novel proximity assay

Aberrant activation of membrane receptors frequently occurs in human carcinomas. Detection of phosphorylated receptors is commonly used as an indicator of receptor activation in formalin-fixed paraffin embedded (FFPE) tumor specimens. FFPE is a standard method of specimen preparation used in the histological analysis of solid tumors. Due to variability in FFPE preparations and the labile nature of protein phosphorylation, measurements of phospho-proteins are unreliable and create ambiguities in clinical interpretation. Here, we describe an alternative, novel approach to measure receptor activation by detecting and quantifying ligand-receptor complexes in FFPE specimens. We used hepatocyte growth factor (HGF)-c-MET as our model ligand-receptor system. HGF is the only known ligand of the c-MET tyrosine kinase receptor and HGF binding triggers c-MET phosphorylation. Novel antibody proximity-based assays were developed and used to detect and quantify total c-MET, total HGF, and HGF-c-MET ligand-receptor interactions in FFPE cell line and tumor tissue. In glioma cells, autocrine activation of c-MET by HGF-c-MET increased basal levels of c-MET phosphorylation at tyrosine (Tyr) 1003. Furthermore, HGF-c-MET activation in glioma cell lines was verified by Surface Protein-Protein Interaction by Crosslinking ELISA (SPPICE) assay in corresponding soluble cell lysates. Finally, we profiled levels ofc-MET, HGF, and HGF-c-MET complexes in FFPE specimens of human Non-Small Cell Lung Cancer (NSCLC), Gastric Cancer, Head and Neck Squamous Cell, and Head and Neck Non-Squamous Cell carcinomas. This report describes a novel approach for the detection and quantification of ligand-receptor interactions that can be widely applied to measure receptor activation in FFPE preclinical models and archived FFPE human tissue specimens.

New strategies in HER2-overexpressing breast cancer: many combinations of targeted drugs available

The anti-HER2 drugs trastuzumab and lapatinib are increasingly changing the natural history of early and metastatic HER2-overexpressing breast cancer. Many other agents targeted against the HER2 signaling network are in clinical development, and these are or will soon be combined with the currently approved anti-HER2 therapies. We review herein recent data in support of the early use of combinations of agents targeted to the HER2 network as the most rational approach against this subtype of breast cancer. We propose that the optimal combination or combinations of anti-HER2 agents delivered early in the natural history of HER2+ breast cancer should close to eliminate acquired drug resistance, shorten the duration of therapy, and potentially dispense with the need of concurrent chemotherapy.

Challenges of introducing new biomarker products for neuropsychiatric disorders into the market

There are many challenges associated with the discovery and development of serum-based biomarkers for psychiatric disorders such as schizophrenia. Here, we review these challenges from the point of view of psychiatrists, general practitioners, the regulatory agencies, and biomarker scientists. There is a general opinion in psychiatric medicine that improvements over the current subjective tests are essential. Despite this, there is a reluctance to accept that peripheral molecules can do the job any better. In addition, psychiatrists find it difficult to accept that peripheral molecules, such as those found in blood, can reflect what is happening in the brain. However, the regulatory health authorities now consider biomarkers as important for the future of drug development and have called for efforts to modernize methods, tools, and techniques for the purpose of developing more efficient and safer drugs. We also describe here the development of the first ever molecular blood test for schizophrenia, and its reception in the market place, as a case in point.

Molecular imaging of HER2-positive breast cancer: a step toward an individualized 'image and treat' strategy

PURPOSE OF REVIEW

HER2 overexpression is correlated with aggressive tumor behavior and poor clinical outcome. Therefore, HER2 has become an important prognostic and predictive factor, as well as a target for molecular therapies. The article reviews recent advances in molecular imaging of HER2 that could facilitate individual approaches to targeted therapy of HER2-positive breast cancers.

RECENT FINDINGS

Because of the heterogeneity of breast cancer and possible discordance in HER2 status between primary tumors and distant metastases, assessment of HER2 expression by noninvasive imaging may become an important complement to immunohistochemistry or fluorescence in-situ hybridization analyses of biopsied tissue. Monoclonal antibodies such as trastuzumab and pertuzumab, or small scaffold proteins such as affibody molecules are used as HER2-targeting agents. For imaging purposes, these agents are labeled with positron or gamma-emitting radionuclides, optical dyes, or paramagnetic contrast molecules for positron emission tomography single photon emission tomography optical, and magnetic resonance imaging, respectively. HER2-specific molecular probes, combined with modern imaging techniques to provide information on HER2 expression not only in primary tumors but also in distant metastases not amenable to biopsy, may reduce problems with false negative results and, thereby, influence patient management by selecting patients that would benefit from HER2-targeted therapies.

SUMMARY

The new 'image and treat' strategy, involving assessment of target presence and distribution in an individual patient followed by optimized, target-specific drug delivery, may potentially improve efficacy of cancer treatment while reducing side effects.

Mechanisms of resistance to anti-human epidermal growth factor receptor 2 agents in breast cancer

Approximately 20% of breast cancers are characterized by overexpression of human epidermal growth factor receptor 2 (HER2) protein and associated gene amplification, and the receptor tyrosine kinase is believed to play a critical role in the pathogenesis of these tumors. The development and implementation of trastuzumab, a humanized monoclonal antibody against the extracellular domain of HER2 protein, has significantly improved treatment outcomes in patients with HER2-overexpressing breast cancer. However, despite this clinical usefulness, unmet needs for better prediction of trastuzumab's response and overcoming primary and acquired resistance remain. In this review, we discuss several potential mechanisms of resistance to trastuzumab that have been closely studied over the last decade. Briefly, these mechanisms include: impaired access of trastuzumab to HER2 by expression of extracellular domain-truncated HER2 (p95 HER2) or overexpression of MUC4; alternative signaling from insulin-like growth factor-1 receptor, other epidermal growth factor receptor family members, or MET; aberrant downstream signaling caused by loss of phosphatase and tensin homologs deleted from chromosome 10 (PTEN), PIK3CA mutation, or downregulation of p27; or FCGR3A polymorphisms. In addition, we discuss potential strategies for overcoming resistance to trastuzumab. Specifically, the epidermal growth factor receptor/HER2 tyrosine kinase inhibitor lapatinib partially overcame trastuzumab resistance in a clinical setting, so its efficacy results and limited data regarding potential mechanisms of resistance to the drug are also discussed.

Profiling protein expression and interactions: proximity ligation as a tool for personalized medicine

The ability to detect very low levels of expressed proteins has enormous potential for early diagnostics and intervention at curable stages of disease. An extended range of targets such as interacting or post-translationally modified proteins can further improve the potential for diagnostics and patient stratification, and for monitoring response to treatment. These are critical building blocks for personalized treatment strategies to manage disease. The past few decades have seen a remarkably improved understanding of the molecular basis of disease in general, and of tumour formation and progression in particular. This accumulated knowledge creates opportunities to develop drugs that specifically target molecules or molecular complexes critical for survival and expansion of tumour cells. However, tumours are highly variable between patients, necessitating the development of diagnostic tools to individualize treatment through parallel analysis of sets of biomarkers. The proximity ligation assay (PLA) can address many of the requirements for advanced molecular analysis. The method builds on the principle that recognition of target proteins by two, three or more antibodies can bring in proximity DNA strands attached to the antibodies. The DNA strands can then participate in ligation reactions, giving rise to molecules that are amplified for highly sensitive detection. PLA is particularly well suited for sensitive, specific and multiplexed analysis of protein expression, post-translational modifications and protein-protein interactions. The analysis of this extended range of biomarkers will prove critical for the development and implementation of personalized medicine.

Comparison of central HER2 testing with quantitative total HER2 expression and HER2 homodimer measurements using a novel proximity-based assay

The accuracy and reliability of immunohistochemical analysis and in situ hybridization for the assessment of HER2 status remains a subject of debate. We developed a novel assay (HERmark Breast Cancer Assay, Monogram Biosciences, South San Francisco, CA) that provides precise quantification of total HER2 protein expression (H2T) and HER2 homodimers (H2D) in formalin-fixed, paraffin-embedded tissue specimens. H2T and H2D results of 237 breast cancers were compared with those of immunohistochemical studies and fluorescence in situ hybridization (FISH) centrally performed at the Mayo Clinic, Rochester, MN. H2T described a continuum across a wide dynamic range ( approximately 2.5 log). Excluding the equivocal cases, HERmark showed 98% concordance with immunohistochemical studies for positive and negative assay values. For the 94 immunohistochemically equivocal cases, 67% and 39% concordance values were observed between HERmark and FISH for positive and negative assay values, respectively. Polysomy 17 in the absence of HER2 gene amplification did not result in HER2 overexpression as evaluated quantitatively using the HERmark assay.

Application of a pharmacogenetic test adoption model to six oncology biomarkers

The ability of genomics to match precise information about the molecular biology of a cancer with the available present and future therapeutics offers tremendous promise for cancer patients. Unfortunately, few genomic-based tests or treatments are available today to benefit these patients. Using a pharmacogenetic test adoption model, previously introduced to model the adoption of HLA-B*5701 testing for abacavir hypersensitivity, six oncology biomarkers, HER2, BCR-ABL quantitation, KRAS mutation, UGT1A1, CYP2D6 for tamoxifen and EGFR expression, test adoption patterns are explored. Developmental milestones and emerging scientific knowledge relating to each of the biomarkers are discussed in the context of their impact on test ordering patterns. Through analysis of the adoption patterns of multiple cancer biomarkers, a pharmacogenetic model emerges which appears to be applicable in five of the six biomarkers. This model may be useful in predicting adoption patterns of new markers and in providing guidance to drug and test developers introducing personalized medicine applications.

Analytical Validation of a Highly Quantitative, Sensitive, Accurate, and Reproducible Assay (HERmark) for the Measurement of HER2 Total Protein and HER2 Homodimers in FFPE Breast Cancer Tumor Specimens

We report here the results of the analytical validation of assays that measure HER2 total protein (H2T) and HER2 homodimer (H2D) expression in Formalin Fixed Paraffin Embedded (FFPE) breast cancer tumors as well as cell line controls. The assays are based on the VeraTag technology platform and are commercially available through a central CAP-accredited clinical reference laboratory. The accuracy of H2T measurements spans a broad dynamic range (2-3 logs) as evaluated by comparison with cross-validating technologies. The measurement of H2T expression demonstrates a sensitivity that is approximately 7–10 times greater than conventional immunohistochemistry (IHC) (HercepTest). The HERmark assay is a quantitative assay that sensitively and reproducibly measures continuous H2T and H2D protein expression levels and therefore may have the potential to stratify patients more accurately with respect to response to HER2-targeted therapies than current methods which rely on semiquantitative protein measurements (IHC) or on indirect assessments of gene amplification (FISH).

Human epidermal growth factor receptor dimerization analysis in breast cancer diagnosis: potential for improving testing accuracy and treatment selection

Our understanding of the human epidermal growth factor receptor (HER) family of proteins has increased over the last few decades. It is clear from the vast assortment of research that has been and is currently being carried out that there is still a lot to be learned. HER dimerization is known to activate various downstream pathways that have an effect on treatment and therapy for breast cancer. HER dimerization acts as a mechanism not only for amplifying the signal pathway but also for signal diversification. There is clear evidence that molecular subtypes of cancer respond differently to different therapeutic options, which challenges the 'one size fits all' approach to chemotherapy in cancer. Here, we review the methods by which HER dimerization can be explored and the potential that this has in the treatment of breast cancer.

Differential survival following trastuzumab treatment based on quantitative HER2 expression and HER2 homodimers in a clinic-based cohort of patients with metastatic breast cancer

Background

We have recently described the correlation between quantitative measures of HER2 expression or HER2 homodimers by the HERmark assay and objective response (RR), time-to progression (TTP), and overall survival (OS) in an expanded access cohort of trastuzumab-treated HER2-positive patients with metastatic breast cancer (MBC) who were stringently selected by fluorescence in situ hybridization (FISH). Multivariate analyses suggested a continuum of HER2 expression that correlated with outcome following trastuzumab. Here we investigate the relationship between HER2 expression or HER2 homodimers and OS in a clinic-based population of patients with MBC selected primarily by IHC.

Methods

HERmark, a proximity-based assay designed to detect and quantitate protein expression and dimerization in formalin-fixed paraffin-embedded (FFPE) tissues, was used to measure HER2 expression and HER2 homodimers in FFPE samples from patients with MBC. Assay results were correlated with OS using univariate Kaplan-Meier, hazard function plots, and multivariate Cox regression analyses.

Results

Initial analyses revealed a parabolic relationship between continuous measures of HER2 expression and risk of death, suggesting that the assumption of linearity for the HER2 expression measurements may be inappropriate in subsequent multivariate analyses. Cox regression analyses using the categorized variable of HER2 expression level demonstrated that higher HER2 levels predicted better survival outcomes following trastuzumab treatment in the high HER2-expressing group.

Conclusions

These data suggest that the quantitative amount of HER2 expression measured by Hermark may be a new useful marker to identify a more relevant target population for trastuzumab treatment in patients with MBC.

EGFR over-expression and activation in high HER2, ER negative breast cancer cell line induces trastuzumab resistance

HER2 is gene amplified or over-expressed in 20-25% of breast cancers resulting in elevated HER2 activation. Trastuzumab (Herceptin), a humanized monoclonal antibody, targets activated HER2 and is clinically effective in HER2-over-expressing breast cancers. However, despite prolonged survival, treated breast cancer patients develop resistance. Resistance to trastuzumab occurs upon inactivation of HER2 regulatory proteins or upon up-regulation of alternative receptors. In particular, elevated levels of EGFR, present in estrogen receptor (ER) positive, trastuzumab-resistant BT-474 xenografts caused, a trastuzumab-resistant phenotype (Ritter et al. Clin Cancer Res 13:4909-4919, 2007). However, the role of EGFR in acquired trastuzumab resistance in ER negative cell models is not well defined. In this study, SKBR3 cell line clones expressing EGFR were generated to examine the role of EGFR over-expression on trastuzumab sensitivity in an, ER-negative breast carcinoma cell line. A stable clone, SKBR3/EGFR (clone 4) expressing moderate levels of EGFR remained sensitive to trastuzumab, whereas a stable clone, SKBR3/EGFR (clone 5) expressing high levels of EGFR, became resistant to trastuzumab. Depletion of EGFR by EGFR small-interfering RNAs in the SKBR3/EGFR (clone 5) reversed trastuzumab resistance. However, the SKBR3/EGFR (clone 5) cell line remained sensitive to lapatinib, an EGFR/HER2 inhibitor. Biochemical analysis using co-immunoprecipitation and proximity-based quantitative VeraTag assays demonstrated that high levels of EGFR phosphorylation, EGFR/EGFR homo-dimerization, and EGFR/HER2 hetero-dimerization were present in the trastuzumab-resistant cells. We conclude that EGFR over-expression can mediate trastuzumab resistance in both ER positive and ER negative cells and hypothesize that a threshold level of EGFR, in the absence of autocrine ligand production, is required to induce the resistant phenotype.

A novel proximity assay for the detection of proteins and protein complexes: quantitation of HER1 and HER2 total protein expression and homodimerization in formalin-fixed, paraffin-embedded cell lines and breast cancer tissue

The availability of drugs targeting the EGFR/HER/erbB signaling pathway has created a need for diagnostics that accurately predict treatment responses. We have developed and characterized a novel assay to provide sensitive and quantitative measures of HER proteins and homodimers in formalin-fixed, paraffin-embedded (FFPE) cell lines and breast tumor tissues, to test these variables. In the VeraTag assay, HER proteins and homodimers are detected through the release of fluorescent tags conjugated to specific HER antibodies, requiring proximity to a second HER antibody. HER2 protein quantification was normalized to tumor area, and compared to receptor numbers in 12 human tumor cell lines determined by fluorescence-activated cell sorting (FACS), and with HER immunohistochemistry (IHC) test categories and histoscores in cell lines and 170 breast tumors. HER1 and HER2 expression levels determined by the VeraTag assay are proportional to receptor number over more than a 2 log10 range, and HER homodimer levels are consistent with crosslinking and immunoprecipitation results. VeraTag HER2 measurements of breast tumor tissue and cell lines correlate with standard IHC test categories (P<0.001). VeraTag HER2 levels also agree with IHC histoscores at lower HER2 protein levels, but are continuous and overlapping between IHC test categories, extending the dynamic range 5-fold to 10-fold at higher HER2 levels. The VeraTag assay specifically and reproducibly measures HER1 and HER2 protein and homodimers in FFPE tissues. The continuous measure of HER2 protein levels over a broad dynamic range, and the novel HER2 homodimer measure, are presently being assessed as predictive markers for responses to targeted HER2 therapy.