An estrogen receptor-negative breast cancer subset characterized by a hormonally regulated transcriptional program and response to androgen

Independent surrogate variable analysis to deconvolve confounding factors in large-scale microarray profiling studies

MOTIVATION

A common difficulty in large-scale microarray studies is the presence of confounding factors, which may significantly skew estimates of statistical significance, cause unreliable feature selection and high false negative rates. To deal with these difficulties, an algorithmic framework known as Surrogate Variable Analysis (SVA) was recently proposed.

RESULTS

Based on the notion that data can be viewed as an interference pattern, reflecting the superposition of independent effects and random noise, we present a modified SVA, called Independent Surrogate Variable Analysis (ISVA), to identify features correlating with a phenotype of interest in the presence of potential confounding factors. Using simulated data, we show that ISVA performs well in identifying confounders as well as outperforming methods which do not adjust for confounding. Using four large-scale Illumina Infinium DNA methylation datasets subject to low signal to noise ratios and substantial confounding by beadchip effects and variable bisulfite conversion efficiency, we show that ISVA improves the identifiability of confounders and that this enables a framework for feature selection that is more robust to model misspecification and heterogeneous phenotypes. Finally, we demonstrate similar improvements of ISVA across four mRNA expression datasets. Thus, ISVA should be useful as a feature selection tool in studies that are subject to confounding.

AVAILABILITY

An R-package isva is available from www.cran.r-project.org.

Pathologic progression of mammary carcinomas in a C3(1)/SV40 T/t-antigen transgenic rat model of human triple-negative and Her2-positive breast cancer

The C3(1) component of the rat prostate steroid binding protein has been used to target expression of the SV40 T/t-antigen to the mammary epithelium of mice resulting in pre-neoplastic lesions that progress to invasive and metastatic cancer with molecular features of human basal-type breast cancer. However, there are major differences in the histologic architecture of the stromal and epithelial elements between the mouse and human mammary glands. The rat mammary gland is more enriched with epithelial and stromal components than the mouse and more closely resembles the cellular composition of the human gland. Additionally, existing rat models of mammary cancer are typically estrogen receptor positive and hormone responsive, unlike most genetically engineered mouse mammary cancer models. In an attempt to develop a mammary cancer model that might more closely resemble the pathology of human breast cancer, we generated a novel C3(1)/SV40 T/t-antigen transgenic rat model that developed progressive mammary lesions leading to highly invasive adenocarcinomas. However, aggressive tumor development prevented the establishment of transgenic lines. Characterization of the tumors revealed that they were primarily estrogen receptor and progesterone receptor negative, and either her2/neu positive or negative, resembling human triple-negative or Her2 positive breast cancer. Tumors expressed the basal marker K14, as well as the luminal marker K18, and were negative for smooth muscle actin. The triple negative phenotype has not been previously reported in a rat mammary cancer model. Further development of a C3(1)SV40 T/t-antigen based model could establish valuable transgenic rat lines that develop basal-type mammary tumors.

Synergy between inhibitors of androgen receptor and MEK has therapeutic implications in estrogen receptor-negative breast cancer

INTRODUCTION

Estrogen receptor-negative (ER-) breast cancer is a heterogeneous disease with limited therapeutic options. The molecular apocrine subtype constitutes 50% of ER-tumors and is characterized by overexpression of steroid response genes including androgen receptor (AR). We have recently identified a positive feedback loop between the AR and extracellular signal-regulated kinase (ERK) signaling pathways in the molecular apocrine subtype. In this feedback loop, AR regulates ERK phosphorylation through the mediation of ErbB2 and, in turn, ERK-CREB1 signaling regulates the transcription of AR in molecular apocrine cells. In this study, we investigated the therapeutic implications of the AR-ERK feedback loop in molecular apocrine breast cancer.

METHODS

We examined a synergy between the AR inhibitor flutamide and the MEK inhibitor CI-1040 in the molecular apocrine cell lines MDA-MB-453, HCC-1954 and HCC-202 using MTT cell viability and annexin V apoptosis assays. Synergy was measured using the combination index (CI) method. Furthermore, we examined in vivo synergy between flutamide and the MEK inhibitor PD0325901 in a xenograft model of the molecular apocrine subtype. The effects of in vivo therapies on tumor growth, cell proliferation and angiogenesis were assessed.

RESULTS

We demonstrate synergistic CI values for combination therapy with flutamide and CI-1040 across three molecular apocrine cell lines at four dose combinations using both cell viability and apoptosis assays. Furthermore, we show in vivo that combination therapy with flutamide and MEK inhibitor PD0325901 has a significantly higher therapeutic efficacy in reducing tumor growth, cellular proliferation and angiogenesis than monotherapy with these agents. Moreover, our data suggested that flutamide and CI-1040 have synergy in trastuzumab resistance models of the molecular apocrine subtype. Notably, the therapeutic effect of combination therapy in trastuzumab-resistant cells was associated with the abrogation of an increased level of ERK phosphorylation that was developed in the process of trastuzumab resistance.

CONCLUSIONS

In this study, we demonstrate in vitro and in vivo synergies between AR and MEK inhibitors in molecular apocrine breast cancer. Furthermore, we show that combination therapy with these inhibitors can overcome trastuzumab resistance in molecular apocrine cells. Therefore, a combination therapy strategy with AR and MEK inhibitors may provide an attractive therapeutic option for the ER-/AR+ subtype of breast cancer.

Relationship between molecular subtype of invasive breast carcinoma and expression of gross cystic disease fluid protein 15 and mammaglobin

We investigated the expression of gross cystic disease fluid protein 15 (GCDFP) and mammaglobin (MGB) by immunohistochemical analysis in 71 invasive breast carcinomas (IBCs) subtyped into luminal (A and B), HER2, basal-like carcinoma (BLC), and unclassified triple-negative carcinoma (UTNC) by established surrogate immunohistochemical profiles. GCDFP and MGB were less likely to be expressed in BLC than in HER2 cancers (P = .000021 and P = .013, respectively) or luminal cancers (P = .00002 and P = .00008, respectively). However, the difference in GCDFP or MGB expression between HER2 and luminal cancers was not significant (P = 1.0 and P = .671, respectively). Our results suggest that luminal cancers demonstrate similar degrees of apocrine differentiation as HER2 cancers. Most BLCs and UTNCs are negative for MGB and GCDFP. Correlation with clinical findings may be needed to exclude the possibility of a metastasis to the breast when BLCs or UTNCs are encountered in a limited sample such as a core biopsy sample.

Trefoil factor 3 is oncogenic and mediates anti-estrogen resistance in human mammary carcinoma

We report herein that trefoil factor 3 (TFF3) is oncogenic and mediates anti-estrogen resistance in human mammary carcinoma. Forced expression of TFF3 in mammary carcinoma cells increased cell proliferation and survival, enhanced anchorage-independent growth, and promoted migration and invasion. Moreover, forced expression of TFF3 increased tumor size in xenograft models. Conversely, depletion of endogenous TFF3 with small interfering RNA (siRNA) decreased the oncogenicity and invasiveness of mammary carcinoma cells. Neutralization of secreted TFF3 by antibody promoted apoptosis, decreased cell growth in vitro, and arrested mammary carcinoma xenograft growth. TFF3 expression was significantly correlated to decreased survival of estrogen receptor (ER)-positive breast cancer patients treated with tamoxifen. Forced expression of TFF3 in mammary carcinoma cells increased ER transcriptional activity, promoted estrogen-independent growth, and produced resistance to tamoxifen and fulvestrant in vitro and to tamoxifen in xenograft models. siRNA-mediated depletion or antibody inhibition of TFF3 significantly enhanced the efficacy of antiestrogens. Increased TFF3 expression was observed in tamoxifen-resistant (TAMR) cells and antibody inhibition of TFF3 in TAMR cells improved tamoxifen sensitivity. Functional antagonism of TFF3 therefore warrants consideration as a novel therapeutic strategy for mammary carcinoma.

ERG cooperates with androgen receptor in regulating trefoil factor 3 in prostate cancer disease progression

To elucidate the role of ETS gene fusions in castration-resistant prostate cancer (CRPC), we characterized the transcriptome of 54 CRPC tumor samples from men with locally advanced or metastatic disease. Trefoil factor 3 (TFF3) emerged as the most highly differentially regulated gene with respect to ERG rearrangement status and resistance to hormone ablation therapy. Conventional chromatin immunoprecipitation (ChIP)-polymerase chain reaction and ChIP followed by DNA sequencing (ChIP-seq) revealed direct binding of ERG to ETS binding sites in the TFF3 promoter in ERG-rearranged prostate cancer cell lines. These results were confirmed in ERG-rearranged hormone-naive prostate cancer (HNPC) and CRPC tissue samples. Functional studies demonstrated that ERG has an inhibitory effect on TFF3 expression in hormone-naive cancer but not in the castration-resistant state. In addition, we provide evidence suggesting an effect of androgen receptor signaling on ERG-regulated TFF3 expression. Furthermore, TFF3 overexpression enhances ERG-mediated cell invasion in CRPC prostate cancer cells. Taken together, our findings reveal a novel mechanism for enhanced tumor cell aggressiveness resulting from ERG rearrangement in the castration-resistant setting through TFF3 gene expression.

Androgen receptor expression and breast cancer survival in postmenopausal women

PURPOSE

Androgen receptor (AR) is commonly expressed in breast cancers. However, the association between tumor AR status and breast cancer survival is uncertain. Hence, we examined the association between AR status and breast cancer survival in the Nurses' Health Study (NHS).

EXPERIMENTAL DESIGN

It was a prospective study of postmenopausal women enrolled in the Nurses' Health Study with stage I to III breast cancer diagnosed between 1976 and 1997 and followed from the date of diagnosis until January 1, 2008 or death. Analyses were conducted using Kaplan-Meier methods and Cox proportional hazard models, to determine the association of AR status with survival outcomes adjusting for covariates.

RESULTS

Among 1467 breast cancers, 78.7% were AR-positive (AR+). Among 1,164 estrogen receptor (ER)-positive cases, 88.0% were AR+. AR positivity was associated with a significant reduction in breast cancer mortality (HR, 0.68; 95% CI, 0.47-0.99) and overall mortality (HR, 0.70; 95% CI, 0.53-0.91) after adjustment for covariates. In contrast, among women with ER-negative tumors (303 cases), 42.9% were AR+. There was a nonsignificant association between AR status and breast cancer death (HR, 1.59; 95% CI, 0.94-2.68).

CONCLUSIONS

The association of AR status and breast cancer survival is dependent on ER status. In particular, AR expression was associated with a more favorable prognosis among women with ER-positive tumors. Thus, determination of AR status may provide additional information on prognosis for postmenopausal women with breast cancer, and provide novel opportunities for targeted therapy.

Androgen receptor expression is significantly associated with better outcomes in estrogen receptor-positive breast cancers

BACKGROUND

The objective of the study was to evaluate the implications of androgen receptor (AR) in breast cancers.

PATIENTS AND METHODS

We investigated immunohistochemical AR expression from the tissue microarrays of 931 patients between 1999 and 2005, and analyzed demographics and outcomes using uni-/multivariate analyses. Tumors with ≥10% nuclear-stained cells were considered positive for AR.

RESULTS

AR was expressed in 58.1% of patients. AR was significantly related to older age at diagnosis, smaller size, well-differentiated tumors, higher positivity of hormone receptors, non-triple-negative breast cancers (non-TNBCs), and lower proliferative index. In estrogen receptor (ER)-negative tumors, AR was distinctively associated with human epidermal growth factor receptor type 2 (HER2) overexpression. With a mean follow-up of 72.7 months, AR was positively related to survival in ER-positive but not in ER-negative tumors. In Cox's models, AR was an independent prognostic factor for disease-free survival in ER-positive cancers. Interestingly, molecular apocrine tumors (ER negative and AR positive) with HER2 positive status showed trends of poorer outcome, but AR had no impact on survival in patients with TNBC.

CONCLUSIONS

AR is significantly associated with favorable features in breast cancers and related to better outcomes in ER-positive not in ER-negative tumors. These results suggest that AR could be an additional marker for endocrine responsiveness in ER-positive cancers and a candidate for therapeutic targeting of ER-negative tumors.

Basal-like and triple-negative breast cancers: a critical review with an emphasis on the implications for pathologists and oncologists

Breast cancer is a heterogeneous disease encompassing a variety of entities with distinct morphological features and clinical behaviors. Although morphology is often associated with the pattern of molecular aberrations in breast cancers, it is also clear that tumors of the same histological type show remarkably different clinical behavior. This is particularly true for 'basal-like cancer', which is an entity defined using gene expression analysis. The purpose of this article was to review the current state of knowledge of basal-like breast cancers, to discuss the relationship between basal-like and triple-negative breast cancers, and to clarify practical implications of these diagnoses for pathologists and oncologists.

Prognostic value of androgen receptor expression in operable triple-negative breast cancer: a retrospective analysis based on a tissue microarray

The aim of this study is to analyze the prognostic value of androgen receptor (AR) expression for patients with triple-negative breast cancer (TNBC). Clinical data of these patients were collected and analyzed, and immunohistochemical staining for AR was performed on tissue microarrays of operable breast cancer from 287 patients with TNBC, who were treated at Sun Yat-sen University Cancer Center from January 1995 to December 2008. AR expression was found in 25.8% of the cases with TNBC. TNBC patients with AR negative have a higher proportion of positive lymph node. A significant correlation was found between AR expression and disease-free survival (DFS) and overall survival (OS). Univariated analysis indicated that AR expression had a significant prognostic value in TNBC patients, whereas multivariate analysis indicated that AR was a significant independent prognostic factor of DFS (P = 0.032) in all patients. Our results suggested that AR was a favorable prognostic factor of DFS and OS in patients with TNBC. Therefore, TNBC may be further divided into two subtypes according to AR status.

Minimising immunohistochemical false negative ER classification using a complementary 23 gene expression signature of ER status

Background

Expression of the oestrogen receptor (ER) in breast cancer predicts benefit from endocrine therapy. Minimising the frequency of false negative ER status classification is essential to identify all patients with ER positive breast cancers who should be offered endocrine therapies in order to improve clinical outcome. In routine oncological practice ER status is determined by semi-quantitative methods such as immunohistochemistry (IHC) or other immunoassays in which the ER expression level is compared to an empirical threshold[1], [2]. The clinical relevance of gene expression-based ER subtypes as compared to IHC-based determination has not been systematically evaluated. Here we attempt to reduce the frequency of false negative ER status classification using two gene expression approaches and compare these methods to IHC based ER status in terms of predictive and prognostic concordance with clinical outcome.

Methodology/Principal Findings

Firstly, ER status was discriminated by fitting the bimodal expression of ESR1 to a mixed Gaussian model. The discriminative power of ESR1 suggested bimodal expression as an efficient way to stratify breast cancer; therefore we identified a set of genes whose expression was both strongly bimodal, mimicking ESR expression status, and highly expressed in breast epithelial cell lines, to derive a 23-gene ER expression signature-based classifier. We assessed our classifiers in seven published breast cancer cohorts by comparing the gene expression-based ER status to IHC-based ER status as a predictor of clinical outcome in both untreated and tamoxifen treated cohorts. In untreated breast cancer cohorts, the 23 gene signature-based ER status provided significantly improved prognostic power compared to IHC-based ER status (P = 0.006). In tamoxifen-treated cohorts, the 23 gene ER expression signature predicted clinical outcome (HR = 2.20, P = 0.00035). These complementary ER signature-based strategies estimated that between 15.1% and 21.8% patients of IHC-based negative ER status would be classified with ER positive breast cancer.

Conclusion/Significance

Expression-based ER status classification may complement IHC to minimise false negative ER status classification and optimise patient stratification for endocrine therapies.

Treatment options for patients with triple-negative breast cancer

Breast cancer is a heterogeneous disease composed of different subtypes, characterized by their different clinicopathological characteristics, prognoses and responses to treatment. In the past decade, significant advances have been made in the treatment of breast cancer sensitive to hormonal treatments, as well as in patients whose malignant cells overexpress or amplify HER2. In contrast, mainly due to the lack of molecular targets, little progress has been made in the treatment of patients with triple-negative breast cancer. Recent improved understanding of the natural history, pathophysiology, and molecular features of triple-negative breast cancers have provided new insights into management and therapeutic strategies for women affected with this entity. Ongoing and planned translational clinical trials are likely to optimize and improve treatment of women with this disease.

DNA amplifications in breast cancer: genotypic-phenotypic correlations

DNA copy number changes in cancer cells, in particular, amplifications, occur frequently, have prognostic impact and are associated with subtypes of breast cancer. Some amplicons contain well-characterized oncogenes, including 11q13 (CCND1) and 17q12 (HER2). HER2 amplification and overexpression defines the HER2+ subgroup of breast cancer patients and is both a prognostic marker for poor outcome and a predictive marker for response to anti-HER2 targeted therapies. Therefore, there is considerable interest in documenting the locations of other recurring amplifications in breast cancers as they may also provide a rich source of new biomarkers and novel therapeutic targets for these subgroups. This article focuses on the genomic profiling of breast cancer, with an emphasis on the characteristics of the amplifications found in subtypes of breast cancer, including luminal (ER+)/HER2(-)), HER2+ and basal-like (ER(-)/HER2(-)), and discusses their known or potential roles in cancer biology and their clinical implications.

Combination of osteopontin and activated leukocyte cell adhesion molecule as potent prognostic discriminators in HER2- and ER-negative breast cancer

BACKGROUND

To analyse the discriminative impact of osteopontin (OPN) and activated leukocyte cell adhesion molecule (ALCAM), combined with human epidermal growth factor 2 (HER2) and oestrogen receptor (ER) in breast cancer.

METHODS

Osteopontin, ALCAM, HER2 and ER mRNA expression in breast cancer tissues of 481 patients were analysed (mRNA microarray analysis, kinetic RT-PCR). Hierarchical clustering was performed in training cohort A (N=100, adjuvant treatment) and validation cohorts B (N=200, no adjuvant treatment, low-risk) and C (N=181, adjuvant treatment, high-risk).

RESULTS

Negative/low ER and HER2, high OPN and low ALCAM mRNA expression helped to identify patients at particularly high risk, showing shorter DFS, P<0.001, and OAS, P=0.001. Although both validation cohorts showed diverse risk and treatment profiles, this marker constellation was concordantly associated with shorter DFS and OAS (P<0.001 and P=0.075 for cohort B and P=0.043 and P<0.001 for cohort C, respectively). In multivariate analysis, this algorithm was the main independent prognostic factor. Cohort B: DFS, P=0.0065, OAS, not significant; cohort C: DFS, P=0.026, OAS, P<0.001.

CONCLUSION

Activated leukocyte cell adhesion molecule and OPN mRNA expression has a strong discriminative impact on survival within cancer patients with low or negative expression of ER and HER2, so called 'high-risk' breast cancers, and might help in identifying patients who could benefit from new treatment approaches like targeted therapies in the adjuvant setting.

Enumerating the gene sets in breast cancer, a "direct" alternative to hierarchical clustering

Background

Two-way hierarchical clustering, with results visualized as heatmaps, has served as the method of choice for exploring structure in large matrices of expression data since the advent of microarrays. While it has delivered important insights, including a typology of breast cancer subtypes, it suffers from instability in the face of gene or sample selection, and an inability to detect small sets that may be dominated by larger sets such as the estrogen-related genes in breast cancer. The rank-based partitioning algorithm introduced in this paper addresses several of these limitations. It delivers results comparable to two-way hierarchical clustering, and much more. Applied systematically across a range of parameter settings, it enumerates all the partition-inducing gene sets in a matrix of expression values.

Results

Applied to four large breast cancer datasets, this alternative exploratory method detects more than thirty sets of co-regulated genes, many of which are conserved across experiments and across platforms. Many of these sets are readily identified in biological terms, e.g., "estrogen", "erbb2", and 8p11-12, and several are clinically significant as prognostic of either increased survival ("adipose", "stromal"...) or diminished survival ("proliferation", "immune/interferon", "histone",...). Of special interest are the sets that effectively factor "immune response" and "stromal signalling".

Conclusion

The gene sets induced by the enumeration include many of the sets reported in the literature. In this regard these inventories confirm and consolidate findings from microarray-based work on breast cancer over the last decade. But, the enumerations also identify gene sets that have not been studied as of yet, some of which are prognostic of survival. The sets induced are robust, biologically meaningful, and serve to reveal a finer structure in existing breast cancer microarrays.

Molecular apocrine differentiation is a common feature of breast cancer in patients with germline PTEN mutations

INTRODUCTION

Breast carcinoma is the main malignant tumor occurring in patients with Cowden disease, a cancer-prone syndrome caused by germline mutation of the tumor suppressor gene PTEN characterized by the occurrence throughout life of hyperplastic, hamartomatous and malignant growths affecting various organs. The absence of known histological features for breast cancer arising in a PTEN-mutant background prompted us to explore them for potential new markers.

METHODS

We first performed a microarray study of three tumors from patients with Cowden disease in the context of a transcriptomic study of 74 familial breast cancers. A subsequent histological and immunohistochemical study including 12 additional cases of Cowden disease breast carcinomas was performed to confirm the microarray data.

RESULTS

Unsupervised clustering of the 74 familial tumors followed the intrinsic gene classification of breast cancer except for a group of five tumors that included the three Cowden tumors. The gene expression profile of the Cowden tumors shows considerable overlap with that of a breast cancer subgroup known as molecular apocrine breast carcinoma, which is suspected to have increased androgenic signaling and shows frequent ERBB2 amplification in sporadic tumors. The histological and immunohistochemical study showed that several cases had apocrine histological features and expressed GGT1, which is a potential new marker for apocrine breast carcinoma.

CONCLUSIONS

These data suggest that activation of the ERBB2-PI3K-AKT pathway by loss of PTEN at early stages of tumorigenesis promotes the formation of breast tumors with apocrine features.

Inhibition of androgen receptor and Cdc25A phosphatase as a combination targeted therapy in molecular apocrine breast cancer

Molecular apocrine breast cancer is an estrogen receptor negative subtype characterized by the over-expression of steroid response genes. In this study we investigate the therapeutic effects of persistent ERK phosphorylation using a Cdc25A phosphatase inhibitor, PM-20 in combination with AR inhibition using flutamide in this subtype. Our findings demonstrate a significant synergy with this combination in reducing cell viability and growth. Furthermore, we show that the mechanism of this effect involves a cross-talk between the AR and ERK signalling pathways. Moreover, using a xenograft molecular apocrine model we demonstrate that the combination therapy results in a significantly better therapeutic response compared to monotherapy and control groups manifesting as reductions in tumor growth, proliferation index, and cellularity. This study demonstrates that the combined application of AR and Cdc25A inhibitors is a promising therapeutic strategy in molecular apocrine breast cancer.

Migrastatin analogues target fascin to block tumour metastasis

Tumour metastasis is the primary cause of death of cancer patients. Development of new therapeutics preventing tumour metastasis is urgently needed. Migrastatin is a natural product secreted by Streptomyces, and synthesized migrastatin analogues such as macroketone are potent inhibitors of metastatic tumour cell migration, invasion and metastasis. Here we show that these migrastatin analogues target the actin-bundling protein fascin to inhibit its activity. X-ray crystal structural studies reveal that migrastatin analogues bind to one of the actin-binding sites on fascin. Our data demonstrate that actin cytoskeletal proteins such as fascin can be explored as new molecular targets for cancer treatment, in a similar manner to the microtubule protein tubulin.

Histological types of breast cancer: how special are they?

Breast cancer is a heterogeneous disease, comprising multiple entities associated with distinctive histological and biological features, clinical presentations and behaviours and responses to therapy. Microarray-based technologies have unravelled the molecular underpinning of several characteristics of breast cancer, including metastatic propensity and histological grade, and have led to the identification of prognostic and predictive gene expression signatures. Furthermore, a molecular taxonomy of breast cancer based on transcriptomic analysis has been proposed. However, microarray studies have primarily focused on invasive ductal carcinomas of no special type. Owing to the relative rarity of special types of breast cancer, information about the biology and clinical behaviour of breast cancers conveyed by histological type has not been taken into account. Histological special types of breast cancer account for up to 25% of all invasive breast cancers. Recent studies have provided direct evidence of the existence of genotypic-phenotypic correlations. For instance, secretory carcinomas of the breast consistently harbour the t(12;15) translocation that leads to the formation of the ETV6-NTRK3 fusion gene, adenoid cystic carcinomas consistently display the t(6;9) MYB-NFIB translocation and lobular carcinomas consistently show inactivation of the CDH1 gene through multiple molecular mechanisms. Furthermore, histopathological and molecular analysis of tumours from conditional mouse models has provided direct evidence for the causative role of specific genes in the genesis of specific histological special types of breast cancer. Here we review the associations between the molecular taxonomy of breast cancer and histological special types, discuss the possible origins of the heterogeneity of breast cancer and propose an approach for the identification of novel therapeutic targets based on the study of histological special types of breast cancer.

Triple-negative breast cancer: role of the androgen receptor

The androgen receptor (AR), a member of the steroid hormone receptor family, is expressed in more than 70% of breast cancers and has been implicated in breast cancer pathogenesis. The role of the AR is of particular interest in patients with estrogen- and progesterone receptor negative and HER2-negative cancers, which represent approximately 25% of all breast cancers. The "triple-negative" subset of tumors generally has a more aggressive clinical course and does not benefit from conventional endocrine targeted therapies. However, emerging evidence suggests that the AR may serve as a therapeutic target for a subset of triple-negative breast cancers. Herein, we review the role of the AR in breast cancer tumorigenesis and current progress and future directions in the development of AR-targeted therapies.

Nuclear localisation of LASP-1 correlates with poor long-term survival in female breast cancer

BACKGROUND

LIM and SH3 protein 1 (LASP-1) is a nucleo-cytoplasmatic signalling protein involved in cell proliferation and migration and is upregulated in breast cancer in vitro studies have shown that LASP-1 might be regulated by prostate-derived ETS factor (PDEF), p53 and/or LASP1 gene amplification. This current study analysed the prognostic significance of LASP-1 on overall survival (OS) in 177 breast cancer patients and addressed the suggested mechanisms of LASP-1-regulation.

METHODS

Nucleo-cytoplasmatic LASP-1-positivity of breast carcinoma samples was correlated with long-term survival, clinicopathological parameters, Ki67-positivity and PDEF expression. Rate of LASP1 amplification was determined in micro-dissected primary breast cancer cells using quantitative RT-PCR. Cell-phase dependency of nuclear LASP-1-localisation was studied in synchronised cells. In addition, LASP-1, PDEF and p53 expression was compared in cell lines of different tumour entities to define principles for LASP-1-regulation.

RESULTS

We showed that LASP-1 overexpression is not due to LASP1 gene amplification. Moreover, no correlation between p53-mutations or PDEF-expression and LASP-1-status was observed. However, nuclear LASP-1-localisation in breast carcinomas is increased during proliferation with peak in G2/M-phase and correlated significantly with Ki67-positivity and poor OS.

CONCLUSION

Our results provide evidence that nuclear LASP-1-positivity may serve as a negative prognostic indicator for long-term survival of breast cancer patients.

EGFR and HER-2/neu expression in invasive apocrine carcinoma of the breast

This study was undertaken to investigate epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER-2)/neu expression in a cohort of apocrine carcinomas of the breast with emphasis on the classification of the breast tumors with apocrine morphology. In total, 55 breast carcinomas morphologically diagnosed as apocrine were evaluated for the steroid receptor expression profile characteristic of normal apocrine epithelium (androgen receptor positive/estrogen receptor (ER) negative/progesterone receptor (PR) negative), and for the expression of EGFR and Her-2/neu proteins, and the copy number ratios of the genes EGFR/CEP7 and HER-2/CEP17. On the basis of the results of steroid receptors expression, 38 (69%) cases were classified as pure apocrine carcinoma (androgen receptor positive/ER negative/PR negative), whereas 17 (31%) were re-classified as apocrine-like carcinomas because they did not have the characteristic steroid receptor expression profile. Her-2/neu overexpression was observed in 54% of the cases (57% pure apocrine carcinomas vs 47% apocrine-like carcinomas). HER-2/neu gene amplification was demonstrated in 52% of all cases (54% pure apocrine carcinomas vs 46% apocrine-like carcinomas). EGFR protein (scores 1 to 3+) was detected in 62% of all cases and was expressed in a higher proportion of pure apocrine carcinomas than in the apocrine-like carcinomas group (76 vs 29%, P=0.006). In the pure apocrine carcinoma group, Her-2/neu and EGFR protein expression were inversely correlated (P=0.006, r=-0.499). EGFR gene amplification was observed in two pure apocrine carcinomas and one apocrine-like carcinoma. Polysomy 7 was commonly present in pure apocrine carcinomas (61 vs 27% of apocrine-like carcinomas; P=0.083) and showed a weak positive correlation with EGFR protein expression (P=0.025, r=0.326). Our study showed that apocrine breast carcinomas are molecularly diverse group of carcinomas. Strictly defined pure apocrine carcinomas are either HER-2-overexpressing breast carcinomas or triple-negative breast carcinomas, whereas apocrine-like carcinomas predominantly belong to the luminal phenotype. Pure apocrine carcinomas show consistent overexpression of either EGFR or HER-2/neu, which could have significant therapeutic implications.

18F-FDG PET of locally invasive breast cancer and association of estrogen receptor status with standardized uptake value: microarray and immunohistochemical analysis

PET imaging is useful for evaluating locally advanced primary breast cancer. Expression of specific molecular markers in these cancers, such as estrogen receptor (ER), progesterone receptor (PR), and HER2 status, has direct prognostic and therapeutic implications in patient management. This study aimed to determine whether a relationship exists between tumor glucose use and important molecular markers in invasive breast cancer. For our purposes, tumor glucose use is quantified by the PET-derived parameter maximum standardized uptake value (SUV).

METHODS

Breast tumors from 36 patients were excised and examined histologically after PET. ER, PR, and HER2 status were determined for all lesions histopathologically. In addition, genomewide expression for a subset of 20 tumors was analyzed using the human genome U133A oligonucleotide microarray.

RESULTS

A significant association was found between estrogen ER status and lesion SUV. ER-negative tumors (n = 17; median SUV, 8.5) demonstrated a significantly higher maximum SUV than did ER-positive tumors (n = 19; median SUV, 4.0) (P < 0.001). No significant association existed between SUV and PR status, HER2/neu status, lymph node involvement, or tumor size. Unsupervised hierarchic clustering of the 20 genetically profiled cancers segregated tumor samples into 2 primary groups of 10 patients each, largely corresponding to ER status.

CONCLUSION

In locally invasive primary breast cancer, ER-negative tumors display higher (18)F-FDG uptake than ER-positive tumors. Microarray analysis confirms these data and identifies genes associated with increased glucose use as measured by PET. These genes significantly overlap those of a previously validated ER-status molecular phenotype. These preliminary data support a growing body of evidence that ER-positive and ER-negative breast cancers have distinct disease-specific patterns. Further validation prospectively and with larger numbers will be required to establish a robust molecular signature for metabolic uptake and patterns of aggressive behavior in advanced breast cancer.

Cyclophosphamide dose intensification may circumvent anthracycline resistance of p53 mutant breast cancers

The predictive value of p53 for the efficacy of front-line anthracycline-based chemotherapy regimens has been a matter of significant controversy. Anthracyclines are usually combined with widely different doses of alkylating agents, which may significantly modulate tumor response to these combinations. We analyzed three series of de novo stage II-III breast cancer patients treated front line with anthracycline-based regimens of various cyclophosphamide dose intensities: 65 patients with estrogen receptor (ER)(-) tumors treated with anthracyclines alone (Institut Jules Bordet, Brussels), 51 unselected breast cancer patients treated with intermediate doses of cyclophosphamide (MD Anderson Cancer Center, Houston, TX), and 128 others treated with a dose-dense anthracycline-cyclophosphamide combination (St. Louis, Paris). After chemotherapy and surgery, pathologic complete response (pCR) was evaluated. p53 status was determined by a yeast functional assay on the pretreatment tumor sample. In a multivariate analysis of the pooled results, a lack of ER expression and high-dose cyclophosphamide administration were associated with a higher likelihood of pCR. A sharp statistical interaction was detected between p53 status and cyclophosphamide dose intensity. Indeed, when restricting our analysis to patients with ER(-) tumors, we confirmed that a mutant p53 status was associated with anthracycline resistance, but found that p53 inactivation was required for response to the dose-intense alkylating regimen. The latter allowed very high levels of pCR in triple-negative tumors. Thus, our data strongly suggest that cyclophosphamide dose intensification in ER(-) p53-mutated breast cancer patients could significantly improve their response.

The contribution of gene expression profiling to breast cancer classification, prognostication and prediction: a retrospective of the last decade

In the last decade, the development of microarrays and the ability to perform massively parallel gene expression analysis of human tumours were received with great excitement by the scientific community. The promise of microarrays was of apocalyptic dimensions, with some experts envisaging that it would be a matter of a few years for this technology to replace traditional clinicopathological markers in clinical practice and treatment decision-making. The replacement of histopathology by high-tech and more objective approaches to cancer diagnosis, prognostication and prediction was, at that time, a foregone conclusion. Ten years after the initial publications of translational research studies using microarrays, one cannot deny that this technology has changed the way breast cancer is perceived. It has brought the concept of breast cancer heterogeneity to the forefront of cancer research, and the fact that distinct subtypes of breast cancer are completely different diseases that affect the same anatomical site. Furthermore, it has led to the development of prognostic and predictive 'gene signatures', which are yet to be fully incorporated into clinical practice. Importantly, though, the prognostic and predictive power of microarrays has been shown to be complementary to, rather than a replacement for, traditional clinicopathological parameters. Here we endeavour to provide a fair and balanced assessment of what microarray-based gene expression analysis has taught us in the last decade and its contribution to breast cancer classification, prognostication and prediction.

Histological and molecular types of breast cancer: is there a unifying taxonomy?

Breast cancer is a complex and heterogeneous disease, comprising multiple tumor entities associated with distinctive histological patterns and different biological features and clinical behaviors. Microarray-based high-throughput technologies have been employed to unravel the molecular characteristics of breast cancer, including its proclivity to disseminate to distant sites, and the molecular basis for histological grade. In addition, a breast cancer molecular taxonomy based solely on transcriptomic analysis has been proposed. Most microarray studies have focused on invasive ductal carcinomas of no special type, neglecting the important information about the biology and clinical behavior of breast cancers conveyed by histological type. Histological special types of breast cancer account for up to 25% of all invasive breast cancers. The histopathological characteristics of these cancers might be driven by specific genetic alterations, providing direct evidence for genotypic-phenotypic correlations between morphological patterns and molecular changes in breast cancer. We review the historical aspects of breast cancer taxonomy, discuss the possible origins of the diversity of breast cancer and propose an approach for the identification of novel therapeutic targets on the basis of histological special types of breast cancer.

Androgen receptor in breast cancer: expression in estrogen receptor-positive tumors and in estrogen receptor-negative tumors with apocrine differentiation

Androgens exert growth inhibitory effects on estrogen receptor and progesterone receptor-negative breast cancer cell lines that show androgen receptor expression. These laboratory findings may be translated into inexpensive alternative therapies for hormone receptor-negative invasive breast cancers. Our aim was to systematically evaluate androgen receptor expression by immunohistochemistry in invasive breast cancers. Androgen receptor (clone AR441, Dako) expression was analyzed on 189 well-characterized consecutive invasive breast carcinomas represented with threefold redundancy on tissue microarrays. Androgen receptor expression was semi-quantitated using a histochemical score-like method and a score >10 was considered positive. Of the 189 consecutive invasive breast cancers, 151 (80%) were positive and 38 (20%) were negative for androgen receptor. The majority (95%) of estrogen receptor-positive tumors were also androgen receptor positive. Of the estrogen receptor-negative tumors, androgen receptor reactivity was seen in 3 of 30 (10%) triple-negative cases and in 5/8 (63%) estrogen receptor-negative/progesterone receptor-negative/HER2+ cases. Six of eight estrogen receptor-negative/androgen receptor-positive cases showed apocrine differentiation. Androgen receptor expression in estrogen receptor-positive cases was associated with smaller tumor size (P=0.0001), lower Nottingham grade (P=0.002) and less frequent tumor cell necrosis (P=0.0001). Androgen receptor expression in estrogen receptor-negative tumors was associated with lower Nottingham grade (P=0.005) and apocrine differentiation (P=0.039). In conclusion, most estrogen receptor-positive breast tumors also express androgen receptor. Androgen receptor expression in estrogen receptor-negative/progesterone receptor-negative/HER2+ tumors (which commonly show apocrine differentiation) and a subset of triple - negative apocrine tumors suggest that these tumors together comprises the 'molecular apocrine' group described previously. However, these findings should be further confirmed on larger series of triple-negative and estrogen negative/progesterone negative/HER2+ tumors. Androgen receptor-targeted therapy in estrogen/progesterone receptor-negative tumors may provide an inexpensive alternative to usual high-dose chemotherapy with or without trastuzumab.

Clinical relevance of the triple-negative breast cancer concept: genetic basis and clinical utility of the concept

The beginning of microarray technology in the 1990s and the sequencing of the human genome in 2000 paved the way for the seminal paper of the Stanford group on the molecular portraits of human breast tumours in the same year. They described four distinct breast cancer subtypes, which they called 'luminal', 'basal', 'HER2-positive', and 'normal breast-like', based on unique gene expression patterns. This paper caused a paradigm shift. Breast cancer was no longer hormone receptor-positive or -negative, but rather luminal, basal or HER2-positive. Since then, numerous papers have appeared, trying to further characterise these subtypes on the DNA, RNA and protein level. Other groups have focussed on the epidemiology, prognosis and outcome after therapy of breast cancer patients according to these molecular subtypes. A promising prognostic marker within the subgroup of basal-like breast cancer is an up-regulated immune response, which is associated with favourable outcome. In addition, the majority of basal-like breast cancers harbour traits of a DNA damage repair defect. This feature can be exploited by the use of DNA damaging agents, and first exciting clinical results of the combination of carboplatin, gemcitabine and a poly (ADP-ribose) polymerase 1 (PARP-1) inhibitor have recently been reported. In this review, the molecular characterisation of triple-negative breast cancer, a proxy for basal-like breast cancer, is described and findings have been put into clinical context.

Emerging roles for XBP1, a sUPeR transcription factor

X-box binding protein 1 (XBP1) is a unique basic region leucine zipper (bZIP) transcription factor whose active form is generated by a nonconventional splicing reaction upon disruption of homeostasis in the endoplasmic reticulum (ER) and activation of the unfolded protein response (UPR). XBP1, first identified as a key regulator of major histocompatibility complex (MHC) class II gene expression in B cells, represents the most conserved signaling component of UPR and is critical for cell fate determination in response to ER stress. Here we review recent advances in our understanding of this multifaceted transcription factor in health and diseases.

Reciprocal regulation of ZEB1 and AR in triple negative breast cancer cells

Zinc-finger enhancer binding protein (ZEB1) is a transcription factor involved in the progression of cancer primarily through promoting epithelial to mesenchymal transition (EMT). ZEB1 represses the expression of E-cadherin by binding to E-box sequences in the promoter, thus decreasing epithelial differentiation. We show that ZEB1 and androgen receptor (AR) cross-talk in triple negative breast cancer cell lines. Chromatin immunoprecipitation analysis demonstrates that ZEB1 binds directly to the E-box located in the AR promoter. ZEB1 suppression by stably transfecting shRNA in a triple negative breast cancer cell line resulted in a decrease of AR mRNA, protein, and AR downstream targets. ZEB1 knockdown in triple negative breast cancer cells sensitized the cells to bicalutamide by reducing migration compared to the control cells. Conversely, blockade of AR signaling with bicalutamide resulted in a suppression of ZEB1 protein expression in two triple negative breast cancer cell lines. Furthermore, using a breast cancer tissue microarray, a majority of triple negative breast cancers exhibit positive staining for both ZEB1 and AR. Taken together, these results indicate that ZEB1 and AR regulate each other to promote cell migration in triple negative breast cancer cells.

Expression of androgen receptors in primary breast cancer

BACKGROUND

To investigate the clinicopathological significance of androgen receptor (AR) expression in primary breast cancers.

PATIENTS AND METHODS

We evaluated AR using immunohistochemistry from 413 whole sections from January 2008 to March 2009 and analyzed the relationship between AR and clinicopathological parameters. Tumors with >/=10% nuclear-stained cells were considered to be positive for AR. The differences among variables were calculated by chi-square test.

RESULTS

The expression rate of AR was 72.9% higher than those of estrogen receptors (ER) and progesterone receptors. AR expression was significant in patients with no elevated preoperative serum cancer antigen 15-3 levels, smaller tumor size, lower histologic grade and hormone receptor-positive and non-triple-negative breast cancer. However, AR expression was observed in 35% of triple-negative cancers. Metaplastic, medullary and mucinous types of carcinomas showed less AR expression. In the ER-negative subgroup, AR was significantly correlated with human epidermal growth factor receptor type 2 (HER-2) overexpression.

CONCLUSIONS

AR is expressed in a significant number of breast cancers and is associated with lower tumor burden and favorable differentiation. There are many issues to be further investigated such as whether AR is an independent prognostic factor, whether it is a therapeutic target for the triple-negative breast cancers and whether it is associated with HER-2 signaling in ER-negative tumors.

Gene expression meta-analysis supports existence of molecular apocrine breast cancer with a role for androgen receptor and implies interactions with ErbB family

Background

Pathway discovery from gene expression data can provide important insight into the relationship between signaling networks and cancer biology. Oncogenic signaling pathways are commonly inferred by comparison with signatures derived from cell lines. We use the Molecular Apocrine subtype of breast cancer to demonstrate our ability to infer pathways directly from patients' gene expression data with pattern analysis algorithms.

Methods

We combine data from two studies that propose the existence of the Molecular Apocrine phenotype. We use quantile normalization and XPN to minimize institutional bias in the data. We use hierarchical clustering, principal components analysis, and comparison of gene signatures derived from Significance Analysis of Microarrays to establish the existence of the Molecular Apocrine subtype and the equivalence of its molecular phenotype across both institutions. Statistical significance was computed using the Fasano & Franceschini test for separation of principal components and the hypergeometric probability formula for significance of overlap in gene signatures. We perform pathway analysis using LeFEminer and Backward Chaining Rule Induction to identify a signaling network that differentiates the subset. We identify a larger cohort of samples in the public domain, and use Gene Shaving and Robust Bayesian Network Analysis to detect pathways that interact with the defining signal.

Results

We demonstrate that the two separately introduced ER^- breast cancer subsets represent the same tumor type, called Molecular Apocrine breast cancer. LeFEminer and Backward Chaining Rule Induction support a role for AR signaling as a pathway that differentiates this subset from others. Gene Shaving and Robust Bayesian Network Analysis detect interactions between the AR pathway, EGFR trafficking signals, and ErbB2.

Conclusion

We propose criteria for meta-analysis that are able to demonstrate statistical significance in establishing molecular equivalence of subsets across institutions. Data mining strategies used here provide an alternative method to comparison with cell lines for discovering seminal pathways and interactions between signaling networks. Analysis of Molecular Apocrine breast cancer implies that therapies targeting AR might be hampered if interactions with ErbB family members are not addressed.

CT-X antigen expression in human breast cancer

Cancer/testis (CT) genes are predominantly expressed in human germ line cells, but not somatic tissues, and frequently become activated in different cancer types. Several CT antigens have already proved to be useful biomarkers and are promising targets for therapeutic cancer vaccines. The aim of the present study was to investigate the expression of CT antigens in breast cancer. Using previously generated massively parallel signature sequencing (MPSS) data, together with 9 publicly available gene expression datasets, the expression pattern of CT antigens located on the X chromosome (CT-X) was interrogated. Whereas a minority of unselected breast cancers was found to contain CT-X transcripts, a significantly higher expression frequency was detected in estrogen and progesterone receptor (ER) negative breast cancer cell lines and primary breast carcinomas. A coordinated pattern of CT-X antigen expression was observed, with MAGEA and NY-ESO-1/CTAG1B being the most prevalent antigens. Immunohistochemical staining confirmed the correlation of CT-X antigen expression and ER negativity in breast tumors and demonstrated a trend for their coexpression with basal cell markers. Because of the limited therapeutic options for ER-negative breast cancers, vaccines based on CT-X antigens might prove to be useful.

Expression of FOXA1 and GATA-3 in breast cancer: the prognostic significance in hormone receptor-negative tumours

Introduction

The expression of additional genes, other than oestrogen receptor (ER), may be important to the hormone-responsive phenotype of breast cancer. Microarray analyses have revealed that forkhead box A1 (FOXA1) and GATA binding protein 3 (GATA-3) are expressed in close association with ERα, both encoding for transcription factors with a potential involvement in the ERα-mediated action in breast cancer. The purpose of this study was to explore if the expression of FOXA1 and GATA-3 may provide an opportunity to stratify subsets of patients that could have better outcome, among the ERα-negative/poor prognosis breast cancer group.

Methods

We evaluate FOXA1 and GATA-3 expression in 249 breast carcinomas by immunohistochemistry, associating it with breast cancer molecular markers, clinicopathological features and patient's survival. The clinicopathological features and immunohistochemical markers of the tumours were compared using the chi-square test and ANOVA. Disease-free survival was analysed through Kaplan–Meier survival curves and Cox regression.

Results

FOXA1 expression was demonstrated in 42% of invasive carcinomas, while GATA-3 was detected in 48% of the cases. FOXA1 expression was inversely associated with tumour size, Nottingham Prognostic Index, histological grade, lymph vascular invasion, lymph node stage and human epidermal growth factor receptor-2 (HER-2) overexpression, while GATA-3 expression showed inverse association with histological grade and HER-2. Both FOXA1 and GATA-3 were directly associated with ERα and progesterone receptor. Among FOXA1-positive tumours, 83.1% are comprised in the luminal A subtype, similar to GATA-3 where 87.7% of positive tumours were classified within this molecular subtype. In the subset of ERα-negative patients, those who were FOXA1-negative had a 3.61-fold increased risk of breast cancer recurrence when compared with the FOXA1-positive.

Conclusions

FOXA1 was a significant predictor of good outcome in breast cancer, whereas GATA-3 was an important luminal marker. The expression of FOXA1 may be used for risk stratification among ERα-negative patients.

Androgen receptor levels and association with PIK3CA mutations and prognosis in breast cancer

PURPOSE

To examine the androgen receptor (AR) levels in breast cancer and to assess the impact of AR expression on patient outcomes.

EXPERIMENTAL DESIGN

Reverse-phase protein arrays were used to measure AR levels and a mass spectroscopy-based approach was used to detect PIK3CA mutations. Means and SDs were generated for AR levels. Linear regression models were used to determine if AR levels differed by tumor subtype and PIK3CA mutation status. Two-sample t tests were used to identify pair-wise differences. Survival probabilities were estimated with the use of the Kaplan-Meier product and log-rank test.

RESULTS

The median age was 59 years (23-89 years). Significant differences in AR levels existed among different breast tumor subtypes (highest in estrogen receptor-positive and/or progesterone receptor-positive tumors) as well as by PIK3CA mutation status (P < 0.0001 for both). AR levels were significantly higher in breast tumors with kinase domain PIK3CA mutations versus tumors that are wild type or with PIK3CA helical mutations (P = 0.017 and P < 0.0001, respectively). In 347 patients, dichotomized AR level by the median was a significant prognostic factor of recurrence-free survival (P = 0.0002) and overall survival (P = 0.004). High AR levels were associated with a significantly improved recurrence-free survival in 207 patients with early-stage estrogen/progesterone receptor-positive tumors after adjuvant hormonal therapy. A trend (P = 0.07) was found toward higher AR expression in PIK3CA mutant versus PIK3CA wild-type triple-negative breast tumors.

CONCLUSIONS

AR levels may represent a prognostic marker in breast cancers and may provide a valuable tool for selecting treatment. There was an association of PIK3CA mutation (kinase domain) with increased AR levels.

FOXA1 in breast cancer

Breast cancer is a heterogeneous disease and classification is important for clinical management. At least five subtypes can be identified based on unique gene expression patterns; this subtype classification is distinct from the histopathological classification. The transcription factor network(s) required for the specific gene expression signature in each of these subtypes is currently being elucidated. The transcription factor network composed of the oestrogen (estrogen) receptor alpha (ERalpha), FOXA1 and GATA3 may control the gene expression pattern in luminal subtype A breast cancers. Breast cancers that are dependent on this network correspond to well-differentiated and hormone-therapy-responsive tumours with good prognosis. In this review, we discuss the interplay between these transcription factors with a particular emphasis on FOXA1 structure and function, and its ability to control ERalpha function. Additionally, we discuss modulators of FOXA1 function, ERalpha-FOXA1-GATA3 downstream targets, and potential therapeutic agents that may increase differentiation through FOXA1.

A functionally significant cross-talk between androgen receptor and ErbB2 pathways in estrogen receptor negative breast cancer

Recent studies have identified novel subgroups in ER-negative breast cancer based on the expression pattern of androgen receptor (AR). One subtype (molecular apocrine) has an over-expression of steroid-response genes and ErbB2. Using breast cancer cell lines with molecular apocrine features, we demonstrate a functional cross-talk between AR and ErbB2 pathways. We show that stimulation of AR and ErbB2 pathways leads to the cross-regulation of gene expression for AR, ErbB2, FOXA1, XBP1, TFF3, and KLK3. As opposed to the physiologic transient phosphorylation of extracellular signal-regulated kinase (ERK1/2) observed with the testosterone treatment, we demonstrate that the addition of ErbB2 inhibition leads to a persistent phosphorylation of ERK1/2, which negatively regulates the downstream signaling and cell growth. This suggests a mechanism for the cross-talk involving the ERK pathway. Moreover, testosterone stimulates the proliferation of molecular apocrine breast cell lines, and this effect can be reversed using antiandrogen flutamide and anti-ErbB2 AG825. Conversely, the growth stimulatory effect of heregulin can also be inhibited with flutamide, suggesting a cross-talk between the AR and ErbB2 pathways affecting cell proliferation. Importantly, there is a synergy with the combined use of flutamide and AG825 on cell proliferation and apoptosis, which indicates a therapeutic advantage in the combined blockage of AR and ErbB2 pathways.

Beyond cytotoxic chemotherapy for the first-line treatment of HER2-negative, hormone-insensitive metastatic breast cancer: current status and future opportunities

As reflected in its varied clinical behavior, appearances under the light microscope, and differential patterns of gene expression, metastatic breast cancer (MBC) is a heterogeneous disease. Systemic treatment decisions are guided by specific tumor characteristics and individual patient factors. For patients with hormone receptor (HR)-negative MBC and for those whose HR-positive disease has become refractory to hormonal therapies, cytotoxic chemotherapy has been the mainstay of systemic treatment. For hormone-insensitive, HER2-positive MBCs, the addition of trastuzumab to chemotherapy has resulted in improved outcomes. Hormone-insensitive MBC lacking HER2 overexpression includes the subset of patients with estrogen receptor/ progesterone receptor/HER2-negative (so-called triple-negative) disease, which represents a significant minority of all breast cancers. Therapeutic options for such patients are limited by the lack of specific targeted approaches, and this heterogeneous group will be considered collectively as well as separately in this overview of existing and emerging treatment strategies. Conventional cytotoxic chemotherapy, alone or in combination, has been the standard first-line treatment for patients with MBC not amenable to antiestrogen or trastuzumab therapy. The recent evaluation of new targeted therapies in combination with cytotoxic agents has created a new type of combination regimen. Agents targeting angiogenesis, the epidermal growth factor receptor, and various signal transduction pathways have been combined with chemotherapy and possess biologic activity in MBC. As these combinations are being investigated, parallel correlative studies aimed at enriching the population who will benefit most are under way.

Global gene expression analysis identifies PDEF transcriptional networks regulating cell migration during cancer progression

Prostate derived ETS factor (PDEF) is an ETS (epithelial-specific E26 transforming sequence) family member that has been identified as a potential tumor suppressor. In multiple invasive breast cancer cells, PDEF expression inhibits cell migration by preventing the acquisition of directional morphological polarity conferred by changes in cytoskeleton organization. In this study, microarray analysis was used to identify >200 human genes that displayed a common differential expression pattern in three invasive breast cancer cell lines after expression of exogenous PDEF protein. Gene ontology associations and data mining analysis identified focal adhesion, adherens junctions, cell adhesion, and actin cytoskeleton regulation as cell migration-associated interaction pathways significantly impacted by PDEF expression. Validation experiments confirmed the differential expression of four cytoskeleton-associated genes with known functional associations with these pathways: uPA, uPAR, LASP1, and VASP. Significantly, chromatin immunoprecipitation studies identified PDEF as a direct negative regulator of the metastasis-associated gene uPA and phenotypic rescue experiments demonstrate that exogenous urokinase plasminogen activator (uPA) expression can restore the migratory ability of invasive breast cancer cells expressing PDEF. Furthermore, immunofluorescence studies identify the subcellular relocalization of urokinase plasminogen activator receptor (uPAR), LIM and SH3 protein (LASP1), and vasodilator-stimulated protein (VASP) as a possible mechanism accounting for the loss of morphological polarity observed upon PDEF expression.

Gene expression profiling of breast cancer

DNA microarray platforms for gene expression profiling were invented relatively recently, and breast cancer has been among the earliest and most intensely studied diseases using this technology. The molecular signatures so identified help reveal the biologic spectrum of breast cancers, provide diagnostic tools as well as prognostic and predictive gene signatures, and may identify new therapeutic targets. Data are best presented in an open access format to facilitate external validation, the most crucial step in identifying robust, reproducible gene signatures suitable for clinical translation. Clinically practical applications derived from full expression profile studies already in use include reduced versions of microarrays representing key discriminatory genes and therapeutic targets, quantitative polymerase chain reaction assays, or immunohistochemical surrogate panels (suitable for application to standard pathology blocks). Prospective trials are now underway to determine the value of such tools for clinical decision making in breast cancer; these efforts may serve as a model for using such approaches in other tumor types.

Comparison and identification of estrogen-receptor related gene expression profiles in breast cancer of different ethnic origins

The interactions between genetic variants in estrogen receptor (ER) have been identified to be associated with an increased risk of breast cancer. Available evidence indicates that genetic variance within a population plays a crucial role in the occurrence of breast cancer. Thus, the comparison and identification of ER-related gene expression profiles in breast cancer of different ethnic origins could be useful for the development of genetic variant cancer therapy. In this study, we performed microarray experiment to measure the gene expression profiles of 59 Taiwanese breast cancer patients; and through comparative bioinformatics analysis against published U.K. datasets, we revealed estrogen-receptor (ER) related gene expression between Taiwanese and British patients. In addition, SNP databases and statistical analysis were used to elucidate the SNPs associated with ER status. Our microarray results indicate that the expression pattern of the 65 genes in ER+ patients was dissimilar from that of the ER- patients. Seventeen mutually exclusive genes in ER-related breast cancer of the two populations with more than one statistically significant SNP in genotype and allele frequency were identified. These 17 genes and their related SNPs may be important in population-specific ER regulation of breast cancer. This study provides a global and feasible approach to study population-unique SNPs in breast cancer of different ethnic origins.

Molecular signatures of neoadjuvant endocrine therapy for breast cancer: characteristics of response or intrinsic resistance

Approximately 30% of patients with estrogen receptor (ER) positive breast cancers exhibit de novo or intrinsic resistance to endocrine therapies. The purpose of this study was to define genes that distinguish ER+ resistant from ER+ responsive tumors, prior to the start of hormone therapies. Previously untreated post-menopausal patients with ER+ breast cancers were treated for 4 months in a neoadjuvant setting with the aromatase inhibitor exemestane alone, or in combination with the antiestrogen tamoxifen. Matched pre- and post-treatment tumor samples from the same patient, were analyzed by gene expression profiling and were correlated with response to treatment. Genes associated with tumor shrinkage achieved by estrogen blockade therapy were identified, as were genes associated with resistance to treatment. Prediction Analysis of Microarrays (PAM) identified 50 genes that can predict response or intrinsic resistance to neoadjuvant endocrine therapy of ER+ tumors, 8 of which have been previously implicated as useful biomarkers in breast cancer. In summary, we identify genes associated with response to endocrine therapy that may distinguish ER+, hormone responsive breast cancers, from ER+ tumors that exhibit intrinsic or de novo resistance. We suggest that the estrogen signaling pathway is aberrant in ER+ tumors with intrinsic resistance. Lastly, the studies show upregulation of a "lipogenic pathway" in non-responsive ER+ tumors that may serve as a marker of intrinsic resistance. This pathway may represent an alternative target for therapeutic intervention.