Deconstructing the molecular portrait of basal-like breast cancer

Rb deletion in mouse mammary progenitors induces luminal-B or basal-like/EMT tumor subtypes depending on p53 status

Breast cancer is a highly heterogeneous disease, with several different subtypes being characterized by distinct histology, gene expression patterns, and genetic alterations. The tumor suppressor gene retinoblastoma 1 (RB1) is frequently lost in both luminal-B and triple-negative tumor (TNT; i.e., estrogen receptor-, progesterone receptor-, and human epidermal growth factor receptor 2-negative) breast cancer subtypes. However, a causal role for RB1 loss in different subtypes remains undefined. Here we report that deletion of Rb alone or together with its relative p107 in mouse mammary stem/bipotent progenitor cells induced focal acinar hyperplasia with squamous metaplasia. These lesions progressed into histologically diverse, transplantable mammary tumors with features of either luminal-B or TNT subtypes. The TNTs included basal-like tumors as well as tumors that exhibited epithelial-to-mesenchymal transition (EMT). The EMT-type tumors and a subset of the basal-like tumors, but not luminal-B-like tumors, expressed mutant forms of the tumor suppressor p53. Accordingly, targeted deletion of both Rb and p53 in stem/bipotent progenitors led to histologically uniform, aggressive, EMT-type tumors. Reintroduction of Rb into these tumor cells suppressed growth in vitro and tumor formation in vivo. These results establish a causal role for Rb loss in breast cancer in mice and demonstrate that cooperating oncogenic events, such as mutations in p53, dictate tumor subtype after Rb inactivation.

Cancer-testis antigen expression in triple-negative breast cancer

BACKGROUND

cancer-testis (CT) antigens, frequently expressed in human germline cells but not in somatic tissues, may become aberrantly reexpressed in different cancer types. The aim of this study was to investigate the expression of CT antigens in breast cancer.

PATIENTS AND METHODS

a total of 100 selected invasive breast cancers, including 50 estrogen receptor (ER) positive/HER2 negative and 50 triple negative (TN), were examined for NY-ESO-1 and MAGE-A expression by immunohistochemistry.

RESULTS

a significantly higher expression of MAGE-A and NY-ESO-1 was detected in TN breast cancers compared with ER-positive tumors (P = 0.04). MAGE-A expression was detected in 13 (26%) TN cancers compared with 5 (10%) ER-positive tumors (P = 0.07). NY-ESO-1 expression was confirmed in nine (18%) TN tumor samples compared with two (4%) ER-positive tumors.

CONCLUSIONS

MAGE-A and NY-ESO-1 CT antigens are expressed in a substantial proportion of TN breast cancers. Because of the limited therapeutic options for this group of patients, CT antigen-based vaccines might prove to be useful for patients with this phenotype of breast cancer.

Genetic susceptibility to breast cancer

Genetic and lifestyle/environmental factors are implicated in the aetiology of breast cancer. This review summarizes the current state of knowledge on rare high penetrance mutations, as well as moderate and low-penetrance genetic variants implicated in breast cancer aetiology. We summarize recent discoveries from large collaborative efforts to combine data from candidate gene studies, and to conduct genome-wide association studies (GWAS), primarily in breast cancers in the general population. These findings are compared with results from collaborative efforts aiming to identify genetic modifiers in BRCA1 and BRCA2 carriers. Breast cancer is a heterogeneous disease, and tumours from BRCA1 and BRCA2 carriers display distinct pathological characteristics when compared with tumours unselected for family history. The relationship between genetic variants and pathological subtypes of breast cancer, and the implication of discoveries of novel genetic variants to risk prediction in BRCA1/2 mutation carriers and in populations unselected for mutation carrier status, are discussed.

Biomarkers for Basal-like Breast Cancer

Initially recognized through microarray-based gene expression profiling, basal-like breast cancer, for which we lack effective targeted therapies, is an aggressive form of carcinoma with a predilection for younger women. With some success, immunohistochemical studies have attempted to reproduce the expression profile classification of breast cancer through identification of subtype-specific biomarkers. This review aims to present an in depth summary and analysis of the current status of basal-like breast cancer biomarker research. While a number of biomarkers show promise for future clinical application, the next logical step is a comprehensive investigation of all biomarkers against a gene expression profile gold standard for breast cancer subtype assignment.

Classical cyclophosphamide, methotrexate, and fluorouracil chemotherapy is more effective in triple-negative, node-negative breast cancer: results from two randomized trials of adjuvant chemoendocrine therapy for node-negative breast cancer

PURPOSE

Retrospective studies suggest that primary breast cancers lacking estrogen receptor (ER) and progesterone receptor (PR) and not overexpressing human epidermal growth factor receptor 2 (HER2; triple-negative tumors) are particularly sensitive to DNA-damaging chemotherapy with alkylating agents.

PATIENTS AND METHODS

Patients enrolled in International Breast Cancer Study Group Trials VIII and IX with node-negative, operable breast cancer and centrally assessed ER, PR, and HER2 were included (n = 2,257). The trials compared three or six courses of adjuvant classical cyclophosphamide, methotrexate, and fluorouracil (CMF) with or without endocrine therapy versus endocrine therapy alone. We explored patterns of recurrence by treatment according to three immunohistochemically defined tumor subtypes: triple negative, HER2 positive and endocrine receptor absent, and endocrine receptor present.

RESULTS

Patients with triple-negative tumors (303 patients; 13%) were significantly more likely to have tumors > 2 cm and grade 3 compared with those in the HER2-positive, endocrine receptor-absent, and endocrine receptor-present subtypes. No clear chemotherapy benefit was observed in endocrine receptor-present disease (hazard ratio [HR], 0.90; 95% CI, 0.74 to 1.11). A statistically significantly greater benefit for chemotherapy versus no chemotherapy was observed in triple-negative breast cancer (HR, 0.46; 95% CI, 0.29 to 0.73; interaction P = .009 v endocrine receptor-present disease). The magnitude of the chemotherapy effect was lower in HER2-positive endocrine receptor-absent disease (HR, 0.58; 95% CI, 0.29 to 1.17; interaction P = .24 v endocrine receptor-present disease).

CONCLUSION

The magnitude of benefit of CMF chemotherapy is largest in patients with triple-negative, node-negative breast cancer.

Triple negative breast cancers: clinical and prognostic implications

Triple negative breast cancers are defined by the absence of oestrogen, progesterone and HER2 expression. Most triple negative cancers display distinct clinical and pathological characteristics with a high proportion of these tumours occurring at a younger age of onset and in African-American women. Triple negative tumours typically demonstrate high histological grade and are the most common breast cancer subtype in BRCA1 carriers. In addition, many of the features of triple negative cancers are similar to those identified in the basal-like molecular subtype which has recently been characterised by gene expression profiling. Although the two groups overlap, they are not synonymous. Triple negative breast cancers are of pivotal clinical importance given the lack of therapeutic options. The prognostic significance of triple negative tumours remains unclear since the group is heterogeneous and worst prognosis seems to be mostly confined to those that express basal cytokeratins or epidermal growth factor receptor (EGFR). This review focuses on outlining the pathological, molecular, and clinical features of triple negative breast cancers, discusses its prognostic value and summarises current therapeutic approaches and future directions of research.

Regulation of alphaB-crystallin gene expression by the transcription factor Ets1 in breast cancer

Recent studies indicate that the small heat shock protein alphaB-crystallin is expressed in poor prognosis basal-like breast tumors and likely contributes to their aggressive phenotype. However, the mechanisms underlying the deregulated expression of alphaB-crystallin in basal-like tumors are poorly understood. Using a bioinformatics approach, we identified a putative DNA binding motif in the human alphaB-crystallin promoter for the proto-oncogene Ets1, a member of the ETS transcription factor family that bind to DNA at palindromic ETS-binding sites (EBS). Here we demonstrate that ectopic expression of Ets1 activates the alphaB-crystallin promoter by an EBS-dependent mechanism and increases alphaB-crystallin protein levels, while silencing Ets1 reduces alphaB-crystallin promoter activity and protein levels. Chromatin immunoprecipitation analyses showed that endogenous Ets1 binds to the alphaB-crystallin promoter in basal-like breast cancer cells in vivo. Interrogation of publically available gene expression data revealed that Ets1 is expressed in human basal-like breast tumors and is associated with poor survival. Collectively, our results point to a previously unrecognized link between the oncogenic transcription factor Ets1 and alphaB-crystallin in basal-like breast cancer.

Cadmium malignantly transforms normal human breast epithelial cells into a basal-like phenotype

BACKGROUND

Breast cancer has recently been linked to cadmium exposure. Although not uniformly supported, it is hypothesized that cadmium acts as a metalloestrogenic carcinogen via the estrogen receptor (ER). Thus, we studied the effects of chronic exposure to cadmium on the normal human breast epithelial cell line MCF-10A, which is ER-negative but can convert to ER-positive during malignant transformation.

METHODS

Cells were continuously exposed to low-level cadmium (2.5 μM) and checked in vitro and by xenograft study for signs of malignant transformation. Transformant cells were molecularly characterized by protein and transcript analysis of key genes in breast cancer.

RESULTS

Over 40 weeks of cadmium exposure, cells showed increasing secretion of matrix metalloproteinase-9, loss of contact inhibition, increased colony formation, and increasing invasion, all typical for cancer cells. Inoculation of cadmium-treated cells into mice produced invasive, metastatic anaplastic carcinoma with myoepithelial components. These cadmium-transformed breast epithelial (CTBE) cells displayed characteristics of basal-like breast carcinoma, including ER-alpha negativity and HER2 (human epidermal growth factor receptor 2) negativity, reduced expression of BRCA1 (breast cancer susceptibility gene 1), and increased CK5 (cytokeratin 5) and p63 expression. CK5 and p63, both breast stem cell markers, were prominently overexpressed in CTBE cell mounds, indicative of persistent proliferation. CTBE cells showed global DNA hypomethylation and c-myc and k-ras overexpression, typical in aggressive breast cancers. CTBE cell xenograft tumors were also ER-alpha negative.

CONCLUSIONS

Cadmium malignantly transforms normal human breast epithelial cells-through a mechanism not requiring ER-alpha-into a basal-like cancer phenotype. Direct cadmium induction of a malignant phenotype in human breast epithelial cells strongly fortifies a potential role in breast cancer.

Gene expression profiling integrated into network modelling reveals heterogeneity in the mechanisms of BRCA1 tumorigenesis

BACKGROUND

Gene expression profiling has distinguished sporadic breast tumour classes with genetic and clinical differences. Less is known about the molecular classification of familial breast tumours, which are generally considered to be less heterogeneous. Here, we describe molecular signatures that define BRCA1 subclasses depending on the expression of the gene encoding for oestrogen receptor, ESR1.

METHODS

For this purpose, we have used the Oncochip v2, a cancer-related cDNA microarray to analyze 14 BRCA1-associated breast tumours.

RESULTS

Signatures were found to be molecularly associated with different biological processes and transcriptional regulatory programs. The signature of ESR1-positive tumours was mainly linked to cell proliferation and regulated by ER, whereas the signature of ESR1-negative tumours was mainly linked to the immune response and possibly regulated by transcription factors of the REL/NFkappaB family. These signatures were then verified in an independent series of familial and sporadic breast tumours, which revealed a possible prognostic value for each subclass. Over-expression of immune response genes seems to be a common feature of ER-negative sporadic and familial breast cancer and may be associated with good prognosis. Interestingly, the ESR1-negative tumours were substratified into two groups presenting slight differences in the magnitude of the expression of immune response transcripts and REL/NFkappaB transcription factors, which could be dependent on the type of BRCA1 germline mutation.

CONCLUSION

This study reveals the molecular complexity of BRCA1 breast tumours, which are found to display similarities to sporadic tumours, and suggests possible prognostic implications.

Multimodal assessment of protein functional deficiency supports pathogenicity of BRCA1 p.V1688del

Unequivocal discrimination between neutral variants and deleterious mutations is crucial for appropriate counseling of individuals with a BRCA1 or BRCA2 sequence change. An increasing number of variants of uncertain significance (VUS) are being identified, the unclassified biological effect of which poses clinical concerns. A multifactorial likelihood-based approach recently suggested disease causality for BRCA1 p.V1688del, a VUS recurrent in Italian breast/ovarian cancer families. Whether and how this single amino acid deletion in the BRCA1 COOH terminus (BRCT) domain affects the function of the mutant protein (DeltaValBRCA1) has not been elucidated. We undertook comprehensive functional characterization of DeltaValBRCA1, comprising comparative structural modeling, analysis of protein stability and associations, and analysis of DNA repair function. Our model predicted BRCT domain destabilization and folding disruption caused by BRCA1 p.V1688del. Consistently, the recombinant DeltaValBRCA1 was less stable than wild-type BRCA1 and, unlike the latter, failed to associate with BRIP1, CtIP, and Rap80 and to relocalize to sites of DNA damage. Yeast two-hybrid analysis revealed a compromised interaction with FHL2 and KPNA2, which is likely responsible for improper subcellular localization of DeltaValBRCA1. In addition, we found four new breast/ovarian cancer families of Italian ancestry who carried this sequence alteration. These results provide the first evidence of the effect of BRCA1 p.V1688del on protein stability and function, supporting the view that it is a deleterious mutation. Multimodal analyses like ours could advance understanding of tumor suppression by BRCA1 and ultimately contribute to developing efficient strategies for screening and characterization of VUS.

Fragile gene product, Fhit, in oxidative and replicative stress responses

Though the fragile histidine triad gene product, Fhit, was discovered and characterized as a tumor suppressor 13 years ago, its sequence, structure, and cellular location did not provide clues to aid discovery of its mechanisms of suppression. Recently, using chemical cross-linkers and immunoprecipitation, a Fhit protein complex was identified that includes Hsp60 and Hsp10 which may mediate Fhit stability and mitochondrial localization, where Fhit binds and stabilizes ferredoxin reductase (Fdxr); when Fdxr is overexpressed, it can lead to production of reactive oxygen species (ROS) that induce apoptosis. Cancer cells expressing endogenous or exogenous Fhit, when exposed to H(2)O(2), an oxidative stress, produce higher levels of apoptosis-inducing ROS than matched, Fhit-negative cells; the Fhit-negative cancer cells survive, carrying DNA damage. In addition to this mitochondrial function, Fhit-overexpression in cancer cells exposed to replicative stress-inducing agents leads to enhanced caspase 3 activation and apoptosis, due to defective Chk1 activation. Thus, damage to the fragile FHIT locus leads to reduced expression of Fhit protein, and makes a two-pronged contribution to development of preneoplastic clonal expansion: (1) absence or reduction of Fhit leads to reduced expression of Fdxr and reduced ROS-induced apoptosis; (2) cells that escape ROS- or replicative stress-induced apoptosis can carry misrepaired DNA damage. The aberrant DNA damage response checkpoint in Fhit-deficient preneoplasias and cancers may make these lesions targets for inhibitors of proteins such as Parp1 and Chk1 with important roles in checkpoint responses, as observed for BRCA1-deficient cancer cells that also exhibit DNA damage repair deficiencies.

Met induces diverse mammary carcinomas in mice and is associated with human basal breast cancer

Understanding the signaling pathways that drive aggressive breast cancers is critical to the development of effective therapeutics. The oncogene MET is associated with decreased survival in breast cancer, yet the role that MET plays in the various breast cancer subtypes is unclear. We describe a knockin mouse with mutationally activated Met (Met(mut)) that develops a high incidence of diverse mammary tumors with basal characteristics, including metaplasia, absence of progesterone receptor and ERBB2 expression, and expression of cytokeratin 5. With gene expression and tissue microarray analysis, we show that high MET expression in human breast cancers significantly correlated with estrogen receptor negative/ERBB2 negative tumors and with basal breast cancers. Few treatment options exist for breast cancers of the basal or trastuzumab-resistant ERBB2 subtypes. We conclude from these studies that MET may play a critical role in the development of the most aggressive breast cancers and may be a rational therapeutic target.

The transcriptional induction of PIK3CA in tumor cells is dependent on the oncoprotein Y-box binding protein-1

PIK3CA, which codes for the p110alpha catalytic subunit of phosphatidylinositol-3-kinase (PI3K), is implicated as an oncogene. Despite importance of PIK3CA in cancer, little is known about what drives up its expression in tumor cells. We recently characterized the PIK3CA promoter and reported that it is transcriptionally silenced by the tumor suppressor protein p53. In the present study, we demonstrate that PIK3CA can be induced by the oncogenic transcription factor Y-box binding protein-1 (YB-1). Three YB-1-responsive elements were identified on the PIK3CA promoter using chromatin immunoprecipitation and electrophoretic mobility shift assays. Interestingly, silencing YB-1 with siRNA in models of basal-like breast cancer decreased p110alpha protein levels regardless of whether PIK3CA was wild type, amplified or mutated. This decrease in p110alpha led to a reduction in PI3K activity and the downstream signaling primarily through p90 ribosomal S6 kinase and S6 ribosomal protein. Disruption in PIK3CA-dependent signaling suppressed cellular invasion correlative with loss of urokinase plasminogen activator (uPA). Similarly, silencing YB-1 suppressed invasion and uPA production however this was reversible through the introduction of constitutively active PIK3CA. In conclusion, YB-1 is the first reported oncogene to induce the expression of PIK3CA through transcriptional control of its promoter.

Gene expression in murine mammary epithelial stem cell-like cells shows similarities to human breast cancer gene expression

Introduction

Mammary stem cells are bipotential and suggested to be the origin of breast cancer development, but are elusive and vaguely characterized. Breast tumors can be divided into subgroups, each one requiring specific treatment. To determine a possible association between mammary stem cells and breast cancer, a detailed characterization of the transcriptome in mammary stem cells is essential.

Methods

We have used a murine mammary epithelial stem-like cell line (HC11) and made a thorough investigation of global gene-expression changes during stepwise differentiation using dual-color comparative microarray technique. Subsequently, we have performed a cross-species comparison to reveal conserved gene expression between stem cells and subtype-specific and prognosis gene signatures, and correlated gene expression to in vivo mammary gland development.

Results

Our analysis of mammary stem-like and stepwise cell differentiation, and an in-depth description of our findings in a breast cancer perspective provide a unique map of the transcriptomic changes and a number of novel mammary stem cell markers. We correlate the alterations to in vivo mammary gland differentiation, and describe novel changes in nuclear receptor gene expression. Interestingly, our comparisons show that specific subtypes of breast cancers with poor prognosis and metastasizing capabilities show resemblance to stem-like gene expression.

Conclusions

The transcriptional characterization of these mammary stem-like cells and their differentiation-induced gene expression patterns is here made widely accessible and provides a basis for research on mammary stem-like cells. Our comparisons suggest that some tumors are more stem-like than others, with a corresponding worse prognosis. This information would, if established, be important for treatment decisions. We also suggest several marker candidates valuable to investigate further.

Hsp90 inhibitor PU-H71, a multimodal inhibitor of malignancy, induces complete responses in triple-negative breast cancer models

Triple-negative breast cancers (TNBCs) are defined by a lack of expression of estrogen, progesterone, and HER2 receptors. Because of the absence of identified targets and targeted therapies, and due to a heterogeneous molecular presentation, treatment guidelines for patients with TNBC include only conventional chemotherapy. Such treatment, while effective for some, leaves others with high rates of early relapse and is not curative for any patient with metastatic disease. Here, we demonstrate that these tumors are sensitive to the heat shock protein 90 (Hsp90) inhibitor PU-H71. Potent and durable anti-tumor effects in TNBC xenografts, including complete response and tumor regression, without toxicity to the host are achieved with this agent. Notably, TNBC tumors respond to retreatment with PU-H71 for several cycles extending for over 5 months without evidence of resistance or toxicity. Through a proteomics approach, we show that multiple oncoproteins involved in tumor proliferation, survival, and invasive potential are in complex with PU-H71-bound Hsp90 in TNBC. PU-H71 induces efficient and sustained downregulation and inactivation, both in vitro and in vivo, of these proteins. Among them, we identify downregulation of components of the Ras/Raf/MAPK pathway and G(2)-M phase to contribute to its anti-proliferative effect, degradation of activated Akt and Bcl-xL to induce apoptosis, and inhibition of activated NF-kappaB, Akt, ERK2, Tyk2, and PKC to reduce TNBC invasive potential. The results identify Hsp90 as a critical and multimodal target in this most difficult to treat breast cancer subtype and support the use of the Hsp90 inhibitor PU-H71 for clinical trials involving patients with TNBC.

Treatment outcomes and clinicopathologic characteristics of triple-negative breast cancer patients who received platinum-containing chemotherapy

The aim of this study was to evaluate the role of platinum-containing chemotherapy for metastatic triple-negative breast cancer (TNBC) patients in terms of the response rate (RR) and progression-free survival. A second aim was to characterize the clinical behavior at the time of relapse of TNBC. We retrospectively analyzed the clinical outcomes of patients with metastatic breast cancer who received taxane-platinum chemotherapy as the first- or second-line treatment, focusing on the TN phenotype. In total, 257 patients with metastatic breast cancer received platinum-containing chemotherapy at Samsung Medical Center from 1999 to 2006. Of these patients, 106 patients with available data on estrogen (ER), progesterone (PgR) and human epidermal growth factor receptor-2 (HER2) receptor status received taxane-platinum regimen as the first- or second-line treatment. The overall RR of patients with TNBC was 39%. This rate did not differ significantly from those of patients with other phenotypes. The time to death after chemotherapy (19 vs. 50 months, p = 0.037) and overall survival (OS) (21 vs. 56 months, p = 0.030) differed significantly between patients with TNBC and non-TNBC. TNBC showed a unique locoregional infiltration pattern at relapse, which might reflect its aggressive clinical behavior. Despite the similar response to platinum-containing chemotherapy, patients with TNBC had a shorter OS than patients with non-TNBC. The implication of TN phenotype as poor prognostic factor is uncertain, because it needs to be defined whether poor outcome is related to the rapid growing characteristics of tumor itself or the resistance to drug therapy. Further prospective studies are warranted.

Fragile histidine triad protein, WW domain-containing oxidoreductase protein Wwox, and activator protein 2gamma expression levels correlate with basal phenotype in breast cancer

BACKGROUND

The expression of fragile histidine triad protein (Fhit) and WW domain-containing oxidoreductase protein (Wwox), tumor suppressors that are encoded by fragile (FRA) loci FRA3B and FRA16D, are lost concordantly in breast cancers. In the current study, the authors examined correlations among Fhit, Wwox, the activator protein 2 transcription factors AP2alpha and AP2gamma, cytokeratins 5 and 6 (CK5/6), epidermal growth factor receptor (EGFR), estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER-2) and their associations with breast cancer phenotypes.

METHODS

Tissue microarrays constructed from 837 breast cancer blocks were immunostained. Expression in >10% of tumor cells was considered positive for cytoplasmic CK5/6, membranous EGFR, and nuclear AP2alpha and AP2gamma. Cytoplasmic Fhit and Wwox staining was scored according to staining intensity. ER, PR, and HER-2 status of tumors was derived from records. Correlations among immunohistochemical markers and tumor subtypes were assessed by univariate and multivariate statistical methods.

RESULTS

Triple-negative tumors had more frequent expression of EGFR, CK5/6 (P < .001), and AP2gamma (P = .003) and more frequent loss of Fhit and Wwox (P < .001), and an inverse correlation was observed between Fhit, Wwox expression and EGFR, ER, and PR expression (P < .001). Reduced Fhit expression was more common in HER-2-positive and AP2gamma-positive cases (P < .001 and P = .002, respectively). There was a direct correlation noted between Fhit and Wwox (P < .001) and a borderline positive relation between AP2alpha and AP2gamma (P = .054).

CONCLUSIONS

The results from this investigation suggested that reduced expression levels of Fhit, Wwox, and nuclear AP2gamma have roles in the pathogenesis of basal-like differentiation in breast cancer. Alteration in the expression of fragile site genes occurs in most of these cancers and may contribute to defects in DNA repair, as observed in breast cancer 1 (BRCA1)-deficient cancers. Thus, DNA damage response checkpoint proteins may be targets for treatment.

Possible Relationship between Basal-Like Breast Carcinoma and Age

SUMMARY: INTRODUCTION: Estrogen receptor expression is lower in breast carcinoma of women ≤45 years compared to women ≥65 years of age, which may imply a higher frequency of basal-like breast carcinomas in younger women. This study evaluated whether there is any difference in the frequency of basal-like phenotype and estrogen receptor (ER)-/HER2- invasive breast carcinomas between women of these 2 different age groups. PATIENTS AND METHODS: A total of 151 women aged ≤45 years or ≥65 years with invasive breast carcinomas were evaluated using tissue microarray, and classified into the following phenotypes: luminal A (ER+/HER2-), luminal B (ER+/HER2+), HER2 overexpression (ER-/HER2+), and basal-like (ER-/HER2- and expressing at least 1 of the basal markers p63, CK5 and/or P-cadherin). RESULTS: ER-/HER2- carcinomas were twice as frequent in women aged ≤45 years (p = 0.0247). However, when the basal-like phenotype was compared with all the other phenotypes grouped together, no statistically significant difference was found (p = 0.0854). CONCLUSIONS: ER-/HER2- carcinomas were more frequent in younger women compared to all the other phenotypes grouped together. An international consensus will be necessary to establish which markers should be used to define basal-like phenotype.

Frequent PTEN genomic alterations and activated phosphatidylinositol 3-kinase pathway in basal-like breast cancer cells

INTRODUCTION

Basal-like carcinomas (BLCs) and human epidermal growth factor receptor 2 overexpressing (HER2+) carcinomas are the subgroups of breast cancers that have the most aggressive clinical behaviour. In contrast to HER2+ carcinomas, no targeted therapy is currently available for the treatment of patients with BLCs. In order to discover potential therapeutic targets, we aimed to discover deregulated signalling pathways in human BLCs.

METHODS

In this study, we focused on the oncogenic phosphatidylinositol 3-kinase (PI3K) pathway in 13 BLCs, and compared it with a control series of 11 hormonal receptor negative- and grade III-matched HER2+ carcinomas. The two tumour populations were first characterised by immunohistochemistry and gene expression. The PI3K pathway was then investigated by gene copy-number analysis, gene expression profiling and at a proteomic level using reverse-phase protein array technology and tissue microarray. The effects of the PI3K inhibition pathway on proliferation and apoptosis was further analysed in three human basal-like cell lines.

RESULTS

The PI3K pathway was found to be activated in BLCs and up-regulated compared with HER2+ tumours as shown by a significantly increased activation of the downstream targets Akt and mTOR (mammalian target of rapamycin). BLCs expressed significantly lower levels of the tumour suppressor PTEN and PTEN levels were significantly negatively correlated with Akt activity within that population. PTEN protein expression correlated significantly with PTEN DNA copy number and more importantly, reduced PTEN DNA copy numbers were observed specifically in BLCs. Similar to human samples, basal-like cell lines exhibited an activation of PI3K/Akt pathway and low/lack PTEN expression. Both PI3K and mTOR inhibitors led to basal-like cell growth arrest. However, apoptosis was specifically observed after PI3K inhibition.

CONCLUSIONS

These data provide insight into the molecular pathogenesis of BLCs and implicate the PTEN-dependent activated Akt signalling pathway as a potential therapeutic target for the management of patients with poor prognosis BLCs.

Development of therapeutic approaches to 'triple negative' phenotype breast cancer

BACKGROUND

Triple negative phenotype (TNP) breast cancers are characterised by the lack of expression of oestrogen and progesterone receptors and of human EGF receptor 2 (HER2) overexpression/amplification. This subgroup of cancers has an aggressive clinical behaviour and is associated with poorer overall survival compared with other subtypes. Given the lack of targets for current tailored therapies in TNP tumours, chemotherapy is the only systemic treatment available; however, overall outcomes remain poor. Therefore, optimal treatment regimens and targeted therapies are urgently needed.

OBJECTIVE

We discuss characteristics of TNP cancers that underpin the rationale of current and novel therapeutic strategies, and an approach for finding and validating new therapeutic targets.

RESULTS/CONCLUSION

The results of large prospective randomised controlled trials are currently awaited. Efforts to unravel the heterogeneity and complexity of TNP cancers using the latest high-throughput molecular techniques and integrating these findings with biology-driven therapeutic strategies in clinical trials will be of paramount importance for the development of treatment approaches for this breast cancer subtype.

Basal-like subtype and BRCA1 dysfunction in breast cancers

Basal-like breast cancers are characterized by their unique expression profile, with the frequent loss of BRCA1, caused by such mechanisms as promoter methylation and the overexpression of high-mobility group proteins of the A type 1 or inhibitor of differentiation 4. Clinicopathologically, basal-like cancers are estrogen receptor-, progesterone receptor-, and human epidermal growth factor receptor type 2 (HER2)-negative; they are of high grade and have a poor prognosis. The fundamental similarity between BRCA1-mutated and basal-like cancers indicates that disruption of BRCA1 may be an essential common initial pathogenic event. Furthermore, p53 mutation and EGFR overexpression occur similarly in BRCA1-mutated and basal-like cancers; these shared alterations provide very important information for understanding not only the genetic and epigenetic carcinogenic pathways in these tumors but also therapeutic strategies. Despite the limited available clinical data about response to chemotherapy, anthracycline-based chemotherapy seems to be effective in a distinct subset of basal-like cancers. Both disrupted BRCA1 and overexpressed topoisomerase II-alpha possibly found in basal-like cancers are speculated to be associated with their increased sensitivity to anthracyclines. If these tumors respond to this chemotherapy, a favorable prognosis might be expected; however, in patients who do not respond, the prognosis is poor. Currently, the sensitivity of basal-like cancers to taxanes is not clear, but considering that these tumors have disrupted mitotic checkpoint function, a poor response may be suggested. On the basis of in vitro studies, BRCA1-disrupted basal-like cancers may be sensitive to DNA-damaging agents including platinum-based compounds, topoisomerase I and II inhibitors, and alkylating agents. In future, new therapeutic approaches for patients with basal-like cancers that are unlikely to respond to chemotherapy should focus on molecules that are involved in the pathogenic pathways of this disease.

Invasive ductal carcinoma of the breast with the "triple-negative" phenotype: prognostic implications of EGFR immunoreactivity

Invasive ductal carcinomas (IDC) of the breast with the triple negative phenotype (steroid hormone receptor absent, negative HER2 status) are characterized by poor clinical outcome. Additional tumor markers might allow identification of patients at higher risk. We evaluated clinical and biological features of 284 consecutive patients with pT1-3, pN1-3 M0 triple-negative IDC. Median follow-up was 70 months (interquartile range 59-94 months). Statistically significant worse disease-free and overall survival were observed in multivariate analysis, for patients with EGFR immunoreactivity in >or=50% invasive tumor cells (HR 2.39, 95% CI, 1.32-4.34, P = 0.004 for DFS; HR 2.34, 95% CI, 1.20-4.59 P = 0.01 for OS). Age >or= 70 years and PVI were additional independent predictors of reduced overall survival. EGFR immunoreactivity significantly correlates with worse prognosis in patients with triple-negative IDC, supporting further studies on the correlation between the degree of EGFR expression and outcome of triple negative breast cancer.

Different gene-expression profiles for the poorly differentiated carcinoma and the highly differentiated papillary adenocarcinoma in mammary glands support distinct metabolic pathways

BACKGROUND

Deregulation of Stat5 in the mammary gland of transgenic mice causes tumorigenesis. Poorly differentiated carcinoma and highly differentiated papillary adenocarcinoma tumors evolve. To distinguish the genes and elucidate the cellular processes and metabolic pathways utilized to preserve these phenotypes, gene-expression profiles were analyzed.

METHODS

Mammary tumors were excised from transgenic mice carrying a constitutively active variant of Stat5, or a Stat5 variant lacking s transactivation domain. These tumors displayed either the carcinoma or the papillary adenocarcinoma phenotypes. cRNAs, prepared from each tumor were hybridized to an Affymetrix GeneChip(R) Mouse Genome 430A 2.0 array. Gene-ontology analysis, hierarchical clustering and biological-pathway analysis were performed to distinct the two types of tumors. Histopathology and immunofluorescence staining complemented the comparison between the tumor phenotypes.

RESULTS

The nucleus-cytoskeleton-plasma membrane axis is a major target for differential gene expression between phenotypes. In the carcinoma, stronger expression of genes coding for specific integrins, cytoskeletal proteins and calcium-binding proteins highlight cell-adhesion and motility features of the tumor cells. This is supported by the higher expression of genes involved in O-glycan synthesis, TGF-beta, activin, their receptors and Smad3, as well as the Notch ligands and members of the gamma-secretase complex that enable Notch nuclear localization. The Wnt pathway was also a target for differential gene expression. Higher expression of genes encoding the degradation complex of the canonical pathway and limited TCF expression in the papillary adenocarcinoma result in membranal accumulation of beta-catenin, in contrast to its nuclear translocation in the carcinoma. Genes involved in cell-cycle arrest at G1 and response to DNA damage were more highly expressed in the papillary adenocarcinomas, as opposed to favored G2/M regulation in the carcinoma tumors.

CONCLUSION

At least six metabolic pathways support the morphological and functional differences between carcinomas and papillary adenocarcinomas. Differential gene-expression profiles favor cell adhesion, motility and proliferation in the carcinoma. Cell-cell contact, polarity, earlier cell-cycle arrest and DNA damage control are better displayed in the papillary adenocarcinoma.

High prevalence of triple-negative tumors in an urban cancer center

BACKGROUND

A disparate proportion of breast cancer deaths occur among young women, those of African-American (AA) ancestry, and particularly young AA women. Estrogen receptors (ER), progesterone receptors (PR), and human epidermal growth factor receptor-2 (HER-2) are key clinically informative biomarkers. The triple-negative (ER-/PR-/HER-2-) tumor subgroup is intrinsically resistant to treatment and portends a poor prognosis. Age, race, and socioeconomic status have been associated with triple-negative tumors (TNT). In the current study, the authors investigated breast cancer subgroups among patients in an urban cancer center serving a multiracial, low socioeconomic population.

METHODS

This case series analyzed female invasive breast cancers diagnosed and/or treated between 2003 and 2004 in the AVON Comprehensive Breast Center at Grady Hospital in Atlanta, Georgia. Data were obtained from the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program, and augmented by the hospital registry and pathology reports. Statistical analyses utilized frequency distributions and logistic regression.

RESULTS

Of 190 breast cancers; 167 (88%) were diagnosed among AA and 23 (12%) were diagnosed among non-AA women. The median age at diagnosis in the 2 groups was 58 years and 57 years, respectively. TNT prevalence was found to differ by race (29.3% among AA women and 13.0% among non-AA women; P = .010). Differences persisted after adjustment for age and stage (odds ratio [OR] of 3.1; 95%confidence interval [95% CI], 0.8-11.6). The majority of recurrences (40.0%) occurred among women with TNT, who were also most likely to experience a fatal event (OR of 3.7; 95%CI, 1.1-13.0).

CONCLUSIONS

Despite a similarity in their age at diagnosis, AA women in our urban cancer center presented with a higher prevalence of TNT and TNT was found to predict the poorest outcomes. Institutional interactive breast conferences and intervention/navigation programs could help to dispel breast cancer disparities and improve outcomes.

An integrative hypothesis about the origin and development of sporadic and familial breast cancer subtypes

Do breast cancer tumours have a common cell origin? Do different breast cancer molecular phenotypes arise from distinct cell types? The studies we have performed during the last few years in familial breast tumours (BRCA1, BRCA2 and non-BRCA1/2) widen questions about the development of sporadic breast cancer to hereditary breast cancer. Array-comparative genomic hybridisation (CGH) studies show universal genomic aberrations in both familial and sporadic breast cancer subtypes that may be selected in the breast tumour development. The inactivation of BRCA1 seems to play a critical role in oestrogen receptor (ER)-negative cancer stem cells (CSCs), driving the tumour development mostly towards a basal-like or, in some cases, to a luminal B phenotype, but other carcinogenetic events are proposed to explain the remaining tumour subtypes. The existence of common genomic alterations in basal-like, ERBB2 and luminal B breast tumours may suggest a common cell origin or clonal selection of these tumour subtypes, arising from an ER-negative CSC or from a progenitor cell (PC). Finally, specific genomic aberrations in ER-positive tumours could provide cellular proliferation advantages when the cells are exposed to oestrogen. We propose a combination of the CSC hypothesis (for the carcinogenesis processes) and the clonal selection model (in terms of tumour development). We uphold that the basal-like-, ERBB2- and luminal B-sporadic and familial tumour subtypes have an ER-negative breast stem/PC origin, whereas luminal A tumours arise from an ER-positive PC, supporting a hierarchical breast carcinogenesis model, whereas crucial genomic imbalances are clonally selected during the tumour development.

Molecular dependence of estrogen receptor-negative breast cancer on a notch-survivin signaling axis

Despite progress in the management of breast cancer, the molecular underpinnings of clinically aggressive subtypes of the disease are not well-understood. Here, we show that activation of Notch developmental signaling in estrogen receptor (ER)-negative breast cancer cells results in direct transcriptional up-regulation of the apoptosis inhibitor and cell cycle regulator survivin. This response is associated with increased expression of survivin at mitosis, enhanced cell proliferation, and heightened viability at cell division. Conversely, targeting Notch signaling with a peptidyl gamma-secretase inhibitor suppressed survivin levels, induced apoptosis, abolished colony formation in soft agar, and inhibited localized and metastatic tumor growth in mice, without organ or systemic toxicity. In contrast, ER+ breast cancer cells, or various normal cell types, were insensitive to Notch stimulation. Therefore, ER- breast cancer cells become dependent on Notch-survivin signaling for their maintenance, in vivo. Therapeutic targeting of this pathway may be explored for individualized treatment of patients with clinically aggressive, ER- breast cancer.

The CD44+/CD24- phenotype is enriched in basal-like breast tumors

Introduction

Human breast tumors are heterogeneous and consist of phenotypically diverse cells. Breast cancer cells with a CD44⁺/CD24^- phenotype have been suggested to have tumor-initiating properties with stem cell-like and invasive features, although it is unclear whether their presence within a tumor has clinical implications. There is also a large heterogeneity between tumors, illustrated by reproducible stratification into various subtypes based on gene expression profiles or histopathological features. We have explored the prevalence of cells with different CD44/CD24 phenotypes within breast cancer subtypes.

Methods

Double-staining immunohistochemistry was used to quantify CD44 and CD24 expression in 240 human breast tumors for which information on other tumor markers and clinical characteristics was available. Gene expression data were also accessible for a cohort of the material.

Results

A considerable heterogeneity in CD44 and CD24 expression was seen both between and within tumors. A complete lack of both proteins was evident in 35% of the tumors, while 13% contained cells of more than one of the CD44⁺/CD24^-, CD44^-/CD24⁺ and CD44⁺/CD24⁺ phenotypes. CD44⁺/CD24^- cells were detected in 31% of the tumors, ranging in proportion from only a few to close to 100% of tumor cells. The CD44⁺/CD24^- phenotype was most common in the basal-like subgroup – characterized as negative for the estrogen and progesterone receptors as well as for HER2, and as positive for cytokeratin 5/14 and/or epidermal growth factor receptor, and particularly common in BRCA1 hereditary tumors, of which 94% contained CD44⁺/CD24^- cells. The CD44⁺/CD24^- phenotype was surprisingly scarce in HER2+ tumors, which had a predominantly CD24⁺ status. A CD44⁺/CD24^- gene expression signature was generated, which included CD44 and α₆-integrin (CD49f) among the top-ranked overexpressed genes.

Conclusion

We demonstrate an association between basal-like and particularly BRCA1 hereditary breast cancer and the presence of CD44⁺/CD24^- cells. Not all basal-like tumors and very few HER2+ tumors, however, contain CD44⁺/CD24^- cells, emphasizing that a putative tumorigenic ability may not be confined to cells of this phenotype and that other breast cancer stem cell markers remain to be identified.

CD151 accelerates breast cancer by regulating alpha 6 integrin function, signaling, and molecular organization

CD151, a master regulator of laminin-binding integrins (alpha(6)beta(4), alpha(6)beta(1), and alpha(3)beta(1)), assembles these integrins into complexes called tetraspanin-enriched microdomains. CD151 protein expression is elevated in 31% of human breast cancers and is even more elevated in high-grade (40%) and estrogen receptor-negative (45%) subtypes. The latter includes triple-negative (estrogen receptor, progesterone receptor, and HER2 negative) basal-like tumors. CD151 ablation markedly reduced basal-like mammary cell migration, invasion, spreading, and signaling (through FAK, Rac1, and lck) while disrupting epidermal growth factor receptor (EGFR)-alpha(6) integrin collaboration. Underlying these defects, CD151 ablation redistributed alpha(6)beta(4) integrins subcellularly and severed molecular links between integrins and tetraspanin-enriched microdomains. In a prototypical basal-like mammary tumor line, CD151 ablation notably delayed tumor progression in ectopic and orthotopic xenograft models. These results (a) establish that CD151-alpha(6) integrin complexes play a functional role in basal-like mammary tumor progression; (b) emphasize that alpha(6) integrins function via CD151 linkage in the context of tetraspanin-enriched microdomains; and (c) point to potential relevance of CD151 as a high-priority therapeutic target, with relative selectivity (compared with laminin-binding integrins) for pathologic rather than normal physiology.

How basal are triple-negative breast cancers?

The basal molecular subtype of breast cancer (BC) is defined by the mRNA expression pattern of an intrinsic approximately 500-gene set. It is the most homogeneous subtype in transcriptional terms, and one of the most aggressive in prognostic terms. Clinical trials testing new systemic therapeutic strategies have been launched in basal BCs. Although no proof of evidence has yet been reported, basal tumors are currently assimilated to and selected as triple-negative (TN) BCs in these trials because of their frequent immunohistochemical (IHC) negativity for hormone and ERBB2 receptors. Here, we have assessed the degrees of correlation and of homogeneity of the TN phenotype (IHC-based definition) and the basal subtype (gene expression-based definition). We analyzed 172 TN BCs defined by gene expression profile as basal (123 cases) and nonbasal (49 cases). Conversely, 160 tumors were defined as basal by their gene expression profile and included 123 TN and 37 non-TN samples. Uni- and multivariate analyses revealed that TN BCs represent a more heterogeneous group than basal BCs, including basal and nonbasal tumors very different both at the histoclinical and molecular level, notably for mRNA expression of molecules targeted by specific therapies under evaluation in clinical trials. These results call for caution in the interpretation of ongoing trials and selection of patients in future trials. They also warrant the identification of molecular markers for basal BCs more clinically applicable than gene expression profiles.

Basal-like breast cancer: a critical review

Recent gene expression profiling of breast cancer has identified specific subtypes with clinical, biologic, and therapeutic implications. The basal-like group of tumors is characterized by an expression signature similar to that of the basal/myoepithelial cells of the breast and is reported to have transcriptomic characteristics similar to those of tumors arising in BRCA1 germline mutation carriers. They are associated with aggressive behavior and poor prognosis, and typically do not express hormone receptors or HER-2 ("triple-negative" phenotype). Therefore, patients with basal-like cancers are unlikely to benefit from currently available targeted systemic therapy. Although basal-like tumors are characterized by distinctive morphologic, genetic, immunophenotypic, and clinical features, neither an accepted consensus on routine clinical identification and definition of this aggressive subtype of breast cancer nor a way of systematically classifying this complex group of tumors has been described. Different definitions are, therefore, likely to produce variable and contradictory results that may hamper consistent identification and development of treatment strategies for these tumors. In this review, we discuss definition, heterogeneity, morphologic spectrum, relation to BRCA1, and clinical significance of this important class of breast cancer.

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.

Regulation of in situ to invasive breast carcinoma transition

The transition of ductal carcinoma in situ (DCIS) to invasive carcinoma is a poorly understood key event in breast tumor progression. Here, we analyzed the role of myoepithelial cells and fibroblasts in the progression of in situ carcinomas using a model of human DCIS and primary breast tumors. Progression to invasion was promoted by fibroblasts and inhibited by normal myoepithelial cells. Molecular profiles of isolated luminal epithelial and myoepithelial cells identified an intricate interaction network involving TGFbeta, Hedgehog, cell adhesion, and p63 required for myoepithelial cell differentiation, the elimination of which resulted in loss of myoepithelial cells and progression to invasion.

The basal-like mammary carcinomas induced by Brca1 or Bard1 inactivation implicate the BRCA1/BARD1 heterodimer in tumor suppression

Women with germ-line mutations of the BRCA1 tumor suppressor gene are highly susceptible to breast and ovarian cancer. The protein product of BRCA1 is involved in a broad spectrum of biological processes and interacts with many diverse proteins. One of these, BARD1, associates with BRCA1 to form a heterodimeric complex that is enzymatically active as an ubiquitin E3 ligase. Although the BRCA1/BARD1 heterodimer has been implicated in several aspects of BRCA1 function, its role in tumor suppression has not been evaluated. To address this question, we generated mouse strains carrying conditional alleles of either Bard1 or Brca1 and used Cre recombination to inactivate these genes in mammary epithelial cells. Significantly, the conditional Bard1- and Brca1-mutant mice developed breast carcinomas that are indistinguishable from each other (and from those of double conditional Bard1/Brca1-mutant animals) with respect to their frequency, latency, histopathology, and cytogenetic features. Reminiscent of the basal-like breast carcinomas seen in human BRCA1 mutation carriers, these tumors are "triple negative" for estrogen and progesterone receptor expression and HER2/neu amplification. They also express basal cytokeratins CK5 and CK14, have an elevated frequency of p53 lesions, and display high levels of chromosomal instability. The remarkable similarities between the mammary carcinomas of Bard1-, Brca1-, and Bard1/Brca1-mutant mice indicate that the tumor suppressor activities of both genes are mediated through the BRCA1/BARD1 heterodimer.

Is triple negative a prognostic factor in breast cancer?

BACKGROUND

Breast cancer is characterized by hormone dependency, and endocrine therapy is a key treatment in breast cancer. Recently, targeted therapies such as Trastuzumab treatment for HER2-positive breast cancer has been important. Triple-negative (TN) breast cancer is characterized by lack of expression of estrogen receptor (ER) and progesterone receptor (PgR), and the absence of HER2 protein overexpression, and so there is no targeted therapy for this subtype. In this study, we examined the biological and prognostic characteristics in TN breast cancer.

PATIENTS AND METHODS

Between January 1998 and September 2006, 1,552 patients with primary breast cancer were investigated retrospectively in this study and ER, PgR and HER2 status were evaluated in all cases. Furthermore, p53 overexpression and Ki67 values were examined immunohistochemically.

RESULTS

Patient distribution according to ER, PgR or HER2 status was as follows: ER and PgR positive: 57.9%, and ER and PgR negative: 25.1%. With regards to the HER2 status, HER2 positive was 23.3%, and triple negative (TN) was 14.0%. TN breast cancer has a high proliferation rate, high nuclear grade and frequent p53 overexpression. Patients with TN tumors had a significantly poorer disease-free survival (DFS) than those with non-TN tumors. After recurrence the overall survival (OS) rate in TN cases was significantly lower than that of the non-TN cases. Multivariate analysis revealed that TN was a significant factor for DFS and OS after recurrence.

CONCLUSION

TN breast cancer is a rare subtype with a high proliferation rate and a high nuclear grade, p53 overexpression, and lower DFS/OS. To improve the prognosis of TN breast cancer, a new effective strategy needs to be developed.

Race and triple negative threats to breast cancer survival: a population-based study in Atlanta, GA

BACKGROUND

Breast cancers with a triple negative tumor (TNT) subtype (as defined by lacking protein expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2)) preclude the use of available targeted therapies and may contribute to poor outcome and to the historically poorest survival observed among African-American (AA) women. This study examines association of the ER/PR/HER2 subtypes with race and breast cancer survival.

METHODS

Breast tumors from a population-based cohort of 116 AA and 360 white Atlanta women aged 20-54, diagnosed from 1990 to 1992 were centrally reviewed and tested by immunohistochemistry. Multivariate survival analyses within subtypes (TNT, ER-PR-HER2+, ER+/PR+HER2+, ER+/PR+HER2-) were conducted using weighted Cox regression and included socio-demographic, prognostic, and treatment factors.

RESULTS

TNTs were more prevalent among young women and particularly among AA women (Odds Ratio [OR] = 1.9, 95% Confidence Interval [CI] 1.2-2.9), adjusting for age, stage, grade, and poverty index. Overall mortality was higher for AA women (Hazard Ratio [HR] = 1.9, 95% CI, 1.5-2.5) and differed by subtypes (P < 0.001). Within the TNT subtype, racial differences in survival persisted, after additional adjustment for treatment and comorbidities (HR = 2.0, 95% CI 1.0-3.7). TNTs were uniquely associated with high expression of p16, p53, and Cyclin E; and low Bcl-2 and Cyclin D1 expression.

CONCLUSIONS

The high prevalence of TNTs among younger women and particularly younger AA women, along with unique protein expression patterns and poorer survival, suggests varying gene-environment etiologies with respect to age and race/ethnicity and a need for effective therapies.

Markers of subtypes in inflammatory breast cancer studied by immunohistochemistry: prominent expression of P-cadherin

Background

Inflammatory breast cancer (IBC) is a distinct and aggressive form of locally-advanced breast cancer with high metastatic potential. In Tunisia, IBC is associated with a high death rate. Among the major molecular subtypes, basal breast carcinomas are poorly differentiated, have metastatic potential and poor prognosis, but respond relatively well to chemotherapy. The aim of this study was to determine the distribution of molecular subtypes in IBC and identify factors that may explain the poor prognosis of IBC.

Methods

To determine breast cancer subtypes we studied by immunohistochemistry the expression of 12 proteins in a series of 91 Tunisian IBC and 541 non-IBC deposited in tissue microarrays.

Results

We considered infiltrating ductal cases only. We found 33.8% of basal cases in IBC vs 15.9% in non-IBC (p < 0.001), 33.3% of ERBB2-overexpressing cases in IBC vs 14.5% in non-IBC (p < 0.001), and 29.3% of luminal cases in IBC vs 59.9% in non-IBC (p < 0.001). The most differentially-expressed protein between IBCs and non-IBCs was P-cadherin. P-cadherin expression was found in 75.9% of all IBC vs 48.2% of all non-IBC (p < 0.001), 95% of IBC vs 69% of non-IBC (p = 0.02) in basal cases, and 82% of IBC vs 43% of non-IBC (p < 0.001) in luminal cases. Logistic regression determined that the most discriminating markers between IBCs and non-IBCs were P-cadherin (OR = 4.9, p = 0.0019) MIB1 (OR = 3.6, p = 0.001), CK14 (OR = 2.7, p = 0.02), and ERBB2 (OR = 2.3, p = 0.06).

Conclusion

Tunisian IBCs are characterized by frequent basal and ERBB2 phenotypes. Surprisingly, luminal IBC also express the basal marker P-cadherin. This profile suggests a specificity that needs further investigation.

Expression profiling technology: its contribution to our understanding of breast cancer

Breast cancer is a complex genetic disease characterized by the accumulation of multiple molecular alterations. Routine clinical management of breast cancer relies on clinical and pathological factors, however. These seem insufficient to reflect the whole clinical heterogeneity of tumours and are less than perfectly adapted to each patient. Recent advances in human genome research and high-throughput molecular technologies have made it possible to tackle the molecular complexity of breast cancer and have contributed to the realization that the biological heterogeneity of breast cancer has implications for treatment. Gene expression profiling of breast cancer has been performed using several approaches. This review will describe the details of gene expression profiling of breast cancer, the different approaches and the impact on clinical management.

RAD51 up-regulation bypasses BRCA1 function and is a common feature of BRCA1-deficient breast tumors

The breast cancer susceptibility gene BRCA1 encodes a large protein thought to contribute to a variety of cellular processes, although the critical determinants of BRCA1-deficient tumorigenesis remain unclear. Given that BRCA1 is required for cell proliferation, suppressor mutations are believed to modify BRCA1 phenotypes and contribute to the etiology of BRCA1-deficient tumors. Here, we show that overexpression of the homologous recombinase RAD51 in a DT40 BRCA1Delta/Delta mutant rescues defects in proliferation, DNA damage survival, and homologous recombination (HR). In addition, epistasis analysis with BRCA1 and the DNA end-joining factor KU70 indicates that these factors operate independently of one another to repair double-strand breaks. Consistent with this genetic finding, cell synchronization studies show that the ability of BRCA1 to promote radioresistance is restricted to the late S and G2 phases of the cell cycle, as predicted for genes whose function is specific to homology-mediated repair rather than nonhomologous end-joining. Notably, retrospective analyses of microarray expression data reveal elevated expression of RAD51 and two of its late-acting cofactors, RAD54 and RAD51AP1, in BRCA1-deficient versus sporadic breast tumors. Taken together, our results indicate that up-regulation of HR provides a permissive genetic context for cells lacking BRCA1 function by circumventing its requirement in RAD51 subnuclear assembly. Furthermore, the data support a model in which enhanced HR activity contributes to the etiology of BRCA1-deficient tumors.

Distinct genomic aberration patterns are found in familial breast cancer associated with different immunohistochemical subtypes

Five breast cancer subtypes have been described in sporadic breast cancer (SBC) using expression arrays: basal-like, ERBB2, normal breast-like, luminal A and B. These molecular subtypes show different genomic aberration patterns (GAPs). Recently, our group described these breast cancer subtypes in 50 non-BRCA1/2 familial tumors using immunohistochemistry assays. We extended this study to the other classes of familial breast cancer (FBC), including 62 tumors (18 BRCA1, 16 BRCA2 and 28 non-BRCA1/2), with the same panel of 25 immunohistochemical (IHC) markers and histological grade obtaining a similar classification. We combined these data with results generated by a 1 Mb BAC array-based CGH study to evaluate the genomic aberrations of each group. We found that BRCA1-related tumors are preferentially basal-like, whereas non-BRCA1/2 familial tumors are mainly luminal A subtype. We described distinct GAPs related to each IHC subtype. Basal tumors had a greater number of gains/losses, while luminal B tumors had more high-level DNA amplifications. Our data are similar to those obtained in SBC studies, highlighting the existence of distinct genetic pathways of tumor evolution, common to both SBC and FBC.

Determining the efficacy of dietary phytochemicals in cancer prevention

Accumulating data suggest that dietary phytochemicals have the potential to moderate deregulated signalling or reinstate checkpoint pathways and apoptosis in damaged cells, while having minimal impact on healthy cells. These are ideal characteristics for chemopreventive and combination anticancer strategies, warranting substantial research effort into harnessing the biological activities of these agents in disease prevention and treatment. However, this requires further investigation into their mode of action and novel approaches to the development of reliable biomarkers.

Triple negative breast carcinoma and the basal phenotype: from expression profiling to clinical practice

Triple negative breast carcinomas (TNBCs) are a group of primary breast tumors with aggressive clinical behavior. Most TNBCs possess a basal phenotype (BP) and show varying degrees of basal cytokeratin and myoepithelial marker expression. The importance of recognizing these tumors came to light largely as the result of gene expression profiling studies that categorized breast cancer into 3 major groups. Two of these groups are defined by their respective expression of estrogen receptor and HER2. TNBCs represent a third group and are defined by negativity for hormone receptors and HER2. TNBCs currently lack effective targeted therapies and are frequently resistant to standard chemotherapeutic regimens. These tumors tend to occur in premenopausal women and members of specific ethnic groups and a subset are associated with heritable BRCA1 mutations. For patients with sporadic TNBCs and BP tumors, BRCA1 dysfunction seems to play a major role in the development and progression of disease. The pathologist's role in the diagnosis and characterization of TNBCs and BP tumors is currently being defined as we are acquiring knowledge of the biologic and genetic underpinnings that drive this heterogeneous group of diseases. This review will provide a historical prospective on TNBCs and tumors that express basal cytokeratins and myoepithelial makers. Additionally, we will discuss the molecular biologic, genetic and pathologic aspects of these tumors. Guidelines will be provided on how to best approach the diagnosis of these cases and on what input pathologists should provide clinicians to help develop optimal therapeutic and preventative strategies against this aggressive group of breast cancers.

Molecular heterogeneity of breast carcinomas and the cancer stem cell hypothesis

Human breast cancers are heterogeneous, both in their pathology and in their molecular profiles. This suggests the hypothesis that breast cancers can initiate in different cell types, either breast epithelial stem cells or their progeny (transit amplifying cells or committed differentiated cells). In this respect, breast cancer could be viewed as being similar to haematological malignancies for which an analogous model has been proposed. Drawing such parallels might help to unravel the molecular nature of the initiating events in breast cancer and might have substantial clinical implications.

The phenotypic spectrum of basal-like breast cancers: a critical appraisal

There are 2 well-recognized cell populations lining the mammary duct system: the epithelial cells lining the lumen and the myoepithelial cells surrounding them. The mammary stem cell, a putative third cell type, has not yet been well characterized. It is not established whether the putative stem cell expresses the full complement, a subset, or none of the markers of normal epithelial and/or myoepithelial cells. However, it is likely that they would have distinctive markers of their own; whether these are retained or lost in their neoplastic progeny is unknown. All 3 cell types may theoretically undergo malignant transformation. Until recently, however, nearly all attention has been focused on carcinomas of epithelial derivation/differentiation. The advent of oligonucleotide and cDNA microarrays has facilitated gene expression profiling of breast cancers, revealing molecular subclasses that may be prognostically relevant. One such subclass, the basal-like breast carcinomas, has been found in numerous independent datasets to be associated with a comparatively worse overall and disease-free survival. These cancers show expression of molecules characteristic of the normal myoepithelial cell, such as basal cytokeratins, and reduced expression of estrogen receptor-related and Erb-B2-related genes and proteins. The classifier genes that formed the basis for the delineation of basal-like carcinomas were derived from datasets that were composed predominantly of ductal type cancers. Therefore, the clinical significance of a basal-like gene expression or immunohistochemical profile in the other breast cancer subtypes is presently unknown. Herein, we evaluate in detail the current state of knowledge on the pathologic features of breast carcinomas classified as basal-like by immunohistochemical and/or gene expression profiling criteria, with an emphasis on their full phenotypic spectrum and also previously underemphasized areas of heterogeneity and ambiguity where present. There seems to be a phenotypic and biologic spectrum of basal-like or myoepithelial-type carcinomas, just as there is a wide range among tumors of luminal epithelial derivation/differentiation. It is critical to promote lucid morphologic definitions of the molecular subtypes, if this information is intended for use in targeted therapies and patient management.

Chromogenic and fluorescent in situ hybridization in breast cancer

Fluorescent (FISH) and chromogenic (CISH) in situ hybridization have recently become part of the diagnostic armamentarium of breast pathologists. HER2 gene testing by FISH and/or CISH has become an integral part of the diagnostic workup for patients with breast cancer. In this era of high throughput technologies, these techniques have proven instrumental for the validation of results from microarray-based comparative genomic hybridization and for the identification of novel oncogenes and tumor suppressor genes. Furthermore, FISH and CISH applied to tissue microarrays have expedited the characterization of genomic changes associated with specific breast cancer molecular subtypes and the identification of novel prognostic and predictive markers. In this review, we provide in this review a critical assessment of CISH and FISH and the impact of the analysis of amplification of specific oncogenes (eg, HER2, EGFR, MYC, CCND1, and FGFR1) and deletion of tumor suppressor genes (eg, BRCA1 and BRCA2) on our understanding of breast cancer.

Use of immunohistochemical markers can refine prognosis in triple negative breast cancer

Background

Basal-like breast cancer has been extensively characterized on the basis of gene expression profiles, but it is becoming increasingly common for these tumors to be defined on the basis of immunohistochemical (IHC) staining patterns, particularly in retrospective studies where material for expression profiling may not be available. The IHC pattern that best defines basal-like tumors is under investigation and various combinations of ER, PR, HER2-, CK5/6+ and EGFR+ have been tested.

Methods

Using datasets from two different hospitals we describe how using different combinations of immunohistochemical patterns has different effects on estimating prognosis at different time intervals after diagnosis. As our baseline, we used two IHC patterns ER-/PR-/HER2-("triple negative phenotype", TNP) and ER-/HER2-/CK5/6+ and/or EGFR+ ("core basal phenotype", CBP).

Results

There was no overall difference in survival between the two hospital-based series, but there was a difference between the TNP and non-TNP groups which was most marked at 3 years (76.8% vs 93.5%, p < .0001). This difference reduced with time, suggesting that long term survivors (beyond 10 years) in the TNP group may have comparable survival to non-TNP cases. A similar difference was seen if CBP was used instead of TNP. However when CK5/6 and/or EGFR expressing tumors were analyzed without consideration of ER/PR status, the reduction in survival increased with time, becoming more pronounced at 10 years than at 3 years.

Conclusion

Our findings suggests that CK5/6 and/or EGFR expressing tumor types have a persistently poorer prognosis over the longer term, an observation that may have important therapeutic implications as drugs that target the EGFR are currently being evaluated in breast cancer.

1,1-Bis(3'-indolyl)-1-(p-biphenyl)methane inhibits basal-like breast cancer growth in athymic nude mice

INTRODUCTION

1,1-Bis (3'-indolyl)-1-(p-biphenyl) methane (CDIM9) has been identified as a new peroxisome proliferator-activated receptor (PPAR)-gamma agonist that exhibits both receptor dependent and independent antitumor activities. CDIM9 has not previously been studied with respect to its effects against basal-like breast cancer. Our goal in the present study was to investigate the anti-basal-like breast tumor activity of CDIM9 in vitro and in vivo.

METHODS

The effects of CDIM9 on cell protein and DNA syntheses were determined in basal-like breast cancer MDA-MB231 and BT549 cells in vitro. Maximum tolerated dose and dose-limited toxicity were determined in BalB/c mice, and antitumor growth activities were assessed in MDA-MB231 basal-like breast tumor xenografts in athymic nude mice.

RESULTS

CDIM9 exhibited selective cell cytotoxicity and anti-proliferation effects on basal-like breast cancer lines. In MDA-MB231 cell, CDIM9 induced caveolin-1 and p27 expression, which was significantly downregulated by co-treatment with the PPAR-gamma antagonist GW9662. Nonsteroidal anti-inflammatory drug-activated gene-1 and activating transcription factor-3 were upregulated by CDIM9 through a PPAR-gamma independent pathway. CDIM9 (40 mg/kg daily, intraperitoneally, for 35 days) inhibited the growth of subcutaneous MDA-MB231 tumor xenografts by 87%, and produced a corresponding decrease in proliferation index. Nearly half of the treated mice (46%) had complete durable remissions, confirmed by histology. The growth of an established tumor was inhibited by CDIM9 treatment (64 mg/kg daily, intraperitoneally, for 10 days), with a mean tumor growth inhibition of 67% as compared with controls. CDIM9 induced increases in tumor caveolin-1 and p27 in vivo, which may contribute to its antitumor activity in basal-like breast cancer.

CONCLUSION

CDIM9 showed potent antiproliferative effects on basal-like breast cancer cell in tissue culture and dramatic growth inhibition in animal models at safe doses. These findings justify further development of this drug for treatment of basal-like breast cancer.