WISP3 (CCN6) is a secreted tumor-suppressor protein that modulates IGF signaling in inflammatory breast cancer

Inflammatory breast cancer: novel preoperative therapies

The treatment of inflammatory breast cancer (IBC) has been hampered by the diagnostic rarity of the disease and its consequent inclusion in clinical trials of preoperative treatment for the more indolent locally advanced breast cancer (LABC). Patients with IBC have a 2-fold greater probability of dying of their disease compared with patients diagnosed with LABC. The aggressive clinical portrait of IBC supports the recent investigative focus on determining molecular changes specific to IBC and developing novel systemic therapies that will favorably affect its poor disease prognosis. A significant amount of laboratory research has been involved in defining a specific "inflammatory signature" for IBC, denoting molecular changes consistently found in IBC. This work has involved human IBC tissue and cell lines and has demonstrated overexpression of several molecules governing metastatic dissemination, such as overexpression of E-cadherin concurrent with a dysfunctional mucin 1. An increased prevalence of mutant TP53, overexpression of RhoC, and vascular endothelial growth factor-A has been found to contribute to the dominant influence of angiogenesis in this disease. A greater understanding of the molecular mechanisms governing the pathophysiology of IBC has led to the development and clinical application of novel targeting agents for preoperative therapy. This study reviews the advances in molecular understanding of IBC and focuses on the efficacy of therapies that target the epidermal growth factor pathway and angiogenesis as well as early investigational therapies involving RhoC and TP53.

The emerging role of CCN6 in breast cancer invasion

The CCN family of matricellular proteins is essential for cell communication and mediation of epithelial stromal cross-talks with roles in development and cancer. In particular, loss of CCN6 messenger RNA expression has been recognized in highly aggressive breast cancers, especially in inflammatory breast cancer and breast cancers with axillary lymph node metastasis. Recent findings can better explain the relevance of CCN6's reduced expression on human invasive breast carcinomas. CCN6 has been shown to play a role in the process of epithelial to mesenchymal transition (EMT), which converts epithelial cells into migratory mesenchymal-like cells with invasive abilities. Although the mechanism by which CCN6 promotes EMT and invasion has not been fully elucidated, current data suggest that it involves the recruitment of the transcriptional regulators Snai1 and ZEB1 to the E-cadherin promoter.

E-cadherin, beta-catenin, and ZEB1 in malignant progression of cancer

The embryonic program 'epithelial-mesenchymal transition' (EMT) is activated during tumor invasion in disseminating cancer cells. Characteristic to these cells is a loss of E-cadherin expression, which can be mediated by EMT-inducing transcriptional repressors, e.g. ZEB1. Consequences of a loss of E-cadherin are an impairment of cell-cell adhesion, which allows detachment of cells, and nuclear localization of beta-catenin. In addition to an accumulation of cancer stem cells, nuclear beta-catenin induces a gene expression pattern favoring tumor invasion, and mounting evidence indicates multiple reciprocal interactions of E-cadherin and beta-catenin with EMT-inducing transcriptional repressors to stabilize an invasive mesenchymal phenotype of epithelial tumor cells.

Normal growth and development in mice over-expressing the CCN family member WISP3

Loss-of-function mutations in the gene WISP3 cause the autosomal recessive human skeletal disease Progressive Pseudorheumatoid Dysplasia, whereas mice with knockout mutations of Wisp3 have no phenotype. The lack of a phenotype in the Wisp3 knockout mice has constrained studies of the protein’s in vivo function. Over-expression experiments in zebrafish indicated that WISP3 may function as a BMP and Wnt signaling modulator. To determine whether these biologic activities are retained in mice, we created two strains of transgenic mice that over-express WISP3 in a broad array of tissues. Despite strong and persistent protein over-expression, the transgenic mice remained phenotypically indistinguishable from their non-transgenic littermates. Surprisingly, WISP3 contained in conditioned medium recovered from transgenic mouse primary kidney cell cultures was able to bind BMP and to inhibit BMP signaling in vitro. Factors that account for the difference between the in vitro and in vivo activities of WISP3 remain unknown. At present, the mouse remains a challenging model organism in which to explore the biologic function of WISP3.

Summary of article. Transgenic mice that broadly over-express WISP3 were created to search for in vivo biologic activities, since mice that lack WISP3 were normal. Surprisingly, transgenic mice were also phenotypically indistinguishable from wild-type animals. The mouse is a challenging model organism in which to explore the biologic function of WISP3.

Genetic changes of Wnt pathway genes are common events in metaplastic carcinomas of the breast

PURPOSE

Metaplastic carcinomas are distinct invasive breast carcinomas with aberrant nonglandular differentiation, which may be spindle, squamous, or chondroid. The limited effective treatments result from the lack of knowledge of its molecular etiology. Given the role of the Wnt pathway in cell fate and in the development of breast cancer, we hypothesized that defects in this pathway may contribute to the development of metaplastic carcinomas.

DESIGN

In 36 primary metaplastic carcinomas, we comprehensively determined the prevalence of and mechanism underlying beta-catenin and Wnt pathway deregulation using immunohistochemistry for beta-catenin expression and localization and mutational analysis for CTNNB1 (encoding beta-catenin), APC, WISP3, AXIN1, and AXIN2 genes. By immunohistochemistry, normal beta-catenin was seen as membrane staining, and it was aberrant when >5% of tumor cells had nuclear or cytoplasmic accumulation or reduced membrane staining.

RESULTS

By immunohistochemistry, aberrant beta-catenin was present in 33 of 36 (92%) cases, revealing deregulation of the Wnt pathway. CTNNB1 missense mutations were detected in 7 of 27 (25.9%) tumors available for mutation analyses. All mutations affected the NH(2)-terminal domain of beta-catenin, presumably rendering the mutant protein resistant to degradation. Two of 27 (7.4%) tumors had mutations of APC, and 5 (18.5%) carried a frame shift mutation of WISP3. No AXIN1 or AXIN2 mutations were found.

CONCLUSIONS

Activation of the Wnt signaling pathway is common in this specific subtype of breast carcinoma. The discovery of CTNNB1, APC, and WISP3 mutations may result in new treatments for patients with metaplastic carcinomas of the breast.

Defining the molecular biology of inflammatory breast cancer

Inflammatory breast cancer (IBC) is a rare, but aggressive form of breast cancer. Despite the progress related to the introduction of primary combination chemotherapy (CT) to the multimodality treatment regimen, the prognosis of IBC remains poor with long-term survival inferior to 50%. Until recently, IBC remained understudied at the molecular level. In the past 10 years, advances have been made in the molecular characterization of the disease. Recently, the use of experimental models and new high-throughput molecular profiling technologies have led to the identification of genes or pathways potentially involved in disease development, which might represent new clinically relevant targets. The aim of this review is to present and discuss what is known about the biology of this particularly aggressive form of breast cancer and to discuss how this knowledge could improve its management.

Inhibition of CCN6 (Wnt-1-induced signaling protein 3) down-regulates E-cadherin in the breast epithelium through induction of snail and ZEB1

The cysteine-rich protein CCN6 [or Wnt-1-induced signaling protein 3 (WISP3)] exerts tumor-suppressive effects in aggressive inflammatory breast cancer. Loss of CCN6 is associated with poorly differentiated phenotypes and increased invasion. Here, we show that reduction of CCN6 expression occurs in 60% of invasive breast carcinomas and is associated with axillary lymph node metastases. Furthermore, low CCN6 expression in invasive carcinoma tissue samples correlates with reduced expression of E-cadherin. In vitro, RNA interference knockdown of CCN6 in two benign human mammary epithelial cell lines (HME and MCF10A) decreased expression of E-cadherin protein and mRNA and reduced activity of the E-cadherin promoter; this reduction was dependent on intact E-box elements. CCN6 knockdown in HME cells resulted in up-regulation of the E-cadherin transcriptional repressors Snail and ZEB1 and enhanced their recruitment and binding to the E-cadherin promoter as analyzed by chromatin immunoprecipitation assays. Small interfering RNA-mediated knockdown of ZEB1 or Snail blocked the down-regulation of E-cadherin caused by CCN6 inhibition. These data show, for the first time, that CCN6 expression is reduced or lost in a substantial number of invasive breast carcinomas and that CCN6 modulates transcriptional repressors of E-cadherin. Together, our results lead to a new hypothesis that Snail and ZEB1 are downstream of CCN6 and play a critical role in CCN6-mediated regulation of E-cadherin in breast cancer.

The CCN family member Wisp3, mutant in progressive pseudorheumatoid dysplasia, modulates BMP and Wnt signaling

In humans, loss-of-function mutations in the gene encoding Wnt1 inducible signaling pathway protein 3 (WISP3) cause the autosomal-recessive skeletal disorder progressive pseudorheumatoid dysplasia (PPD). However, in mice there is no apparent phenotype caused by Wisp3 deficiency or overexpression. Consequently, the in vivo activities of Wisp3 have remained elusive. We cloned the zebrafish ortholog of Wisp3 and investigated its biologic activity in vivo using gain-of-function and loss-of-function approaches. Overexpression of zebrafish Wisp3 protein inhibited bone morphogenetic protein (BMP) and Wnt signaling in developing zebrafish. Conditioned medium-containing zebrafish and human Wisp3 also inhibited BMP and Wnt signaling in mammalian cells by binding to BMP ligand and to the Wnt coreceptors low-density lipoprotein receptor-related protein 6 (LRP6) and Frizzled, respectively. Wisp3 proteins containing disease-causing amino acid substitutions found in patients with PPD had reduced activity in these assays. Morpholino-mediated inhibition of zebrafish Wisp3 protein expression in developing zebrafish affected pharyngeal cartilage size and shape. These data provide a biologic assay for Wisp3, reveal a role for Wisp3 during zebrafish cartilage development, and suggest that dysregulation of BMP and/or Wnt signaling contributes to cartilage failure in humans with PPD.

Unique bisphenol A transcriptome in prostate cancer: novel effects on ERbeta expression that correspond to androgen receptor mutation status

BACKGROUND

Prostatic adenocarcinomas are dependent on androgen receptor (AR) activity for growth and progression, and therapy for disseminated disease depends on ablation of AR activity. Recurrent tumors ultimately arise wherein AR has been re-activated. One mechanism of AR restoration is via somatic mutation, wherein cells containing mutant receptors become susceptible to activation by alternative ligands, including bisphenol A (BPA). In tumors with specific AR mutations, BPA promotes therapeutic bypass, suggesting significant negative impact to the clinical management of prostate cancer.

OBJECTIVE

Our goal was to determine the mechanism of BPA action in cancer cells carrying BPA-responsive AR mutants.

METHODS

The molecular signature of BPA activity in prostate cancer cells harboring mutant AR was delineated via genetic microarray analysis. Specificity of BPA action was assessed by comparison with the molecular signature elicited by dihydrotestosterone (DHT).

RESULTS

BPA and DHT elicited distinct transcriptional signatures in prostate cancer cells expressing the BPA-responsive mutant AR-T877A. BPA dramatically attenuated estrogen receptor beta (ERbeta) expression; this finding was specific to prostate tumor cells in which BPA induces cellular proliferation.

CONCLUSIONS

BPA induces a distinct gene expression signature in prostate cancer cells expressing somatic AR mutation, and a major molecular consequence of BPA action is down-regulation of ERbeta. Since ERbeta functions to antagonize AR function and AR-dependent proliferation, these findings reveal a novel mechanism by which BPA likely regulates cellular proliferation. Future investigation directed at dissecting the importance of ERbeta in the proliferative response to BPA will establish the contribution of this event to adverse effects associated with human exposure.

Downregulation of CCN3 expression as a potential mechanism for melanoma progression

Coculture of human melanocytes with keratinocytes upregulates CCN3, a matricellular protein critical to maintenance of normal homeostasis of melanocytes in the skin. CCN3 affects two fundamental features of melanocyte physiology: it inhibits melanocyte proliferation and stimulates their adhesion to the basement membrane. Here we report that expression of CCN3 is downregulated in advanced melanomas. Aggressive melanoma cell lines did not respond to treatment with CCN3 inducers, such as interleukin-1beta (IL-1beta), while less aggressive melanoma cell lines responded similarly to melanocytes. Immunostaining analyses revealed that CCN3 was present in melanoma cells close to the epidermal-dermal interface, but not in melanoma cells that had invaded deep into the dermis or had metastasized to lymph nodes. Contrary to our expectations, overexpression of CCN3 in 1205Lu metastatic melanoma cells did not affect their adhesion to collagen IV. However, CCN3 decreased the transcription and activation of matrix metalloproteinases and suppressed the invasion of 1205Lu melanoma cells. These results suggest that the lack of CCN3 in advanced melanoma cells contributes to their invasive phenotype. Whereas major matricellular proteins, such as osteopontin, tenascin or secreted protein acidic and rich in cysteine (SPARC), are strongly upregulated in melanoma cells; CCN3 is the first member of this family that is downregulated.

CCN6 (WISP3) as a new regulator of the epithelial phenotype in breast cancer

CCN6 (WISP3) is a cysteine-rich secreted protein that belongs to the CCN (Cyr61, CTGF, Nov) family of genes. We found that CCN6 mRNA is reduced in 80% of cases of the most lethal form of locally advanced breast cancer, inflammatory breast cancer. CCN6 contains four highly conserved motifs with sequence similarities to insulin-like growth factor binding proteins, von Willebrand type C, thrombospondin 1, and a carboxyl-terminal domain putatively involved in dimerization. CCN6 has tumor growth-, proliferation-, and invasion-inhibitory functions in breast cancer. Recently, by using a small infering RNA to downregulate CCN6 in immortalized human mammary epithelial cells, CCN6 was found to be essential to induce the process of epithelial-mesenchymal transition (EMT) with repression of E-cadherin gene expression and induction of a protein expression program characteristic of EMT. This review will focus on the current knowledge regarding the function of CCN6 in breast cancer with special emphasis on the emerging role of CCN6 as a regulator of the epithelial phenotype and E-cadherin expression in the breast.

Differential Expression and Prognostic Implications of the CCN Family Members WISP-1, WISP-2, and WISP-3 in Human Breast Cancer

BACKGROUND

The CCN family has three Wnt-inducted secreted proteins named WISP-1, WISP-2 and WISP-3. These molecules are known to play a diverse role in cells, but their role in cancer cells remains controversial.

METHODS

In this study, we analyzed the expression of the three WISP molecules at the mRNA and protein levels in a cohort of 122 human breast tumors and 32 normal breast tissues, and we correlated these findings with patients' clinical outcomes.

RESULTS

WISP-1 transcripts were found in lower levels in node-positive tumors compared with node-negative tumors (P < .05); were lower in patients with a moderate (P = .01) and poor Nottingham Prognostic Index prognosis (P < .05) compared with good prognostic groups; were of significantly lower level in grade 3 differentiated tumors (P < .05) compared with grade 1; and were of lower levels in patients who developed metastasis and died from breast cancer-related causes (P < .05 in both comparisons). Almost the reverse was found to be true for WISP-2, which had greater levels of expression in node-positive tumors (P = .0043); higher levels in both moderate and poor prognostic groups compared with the good prognostic group (both P < .05); greater level in both grade 2 and 3 when compared with grade 1 (both P < .05); and higher levels in patients who went on to develop metastases (P < .01). WISP-3 transcript levels showed no statistically significant differences between groups.

CONCLUSIONS

WISPs may play important but contrasting roles in breast cancer. WISP-1 seems to act as a tumor suppressor and WISP-2 as a factor that stimulates aggressiveness; WISP-3 has no definable beneficial or detrimental role.

Mutant WISP3 triggers the phenotype shift of articular chondrocytes by promoting sensitivity to IGF-1 hypothesis of spondyloepiphyseal dysplasia tarda with progressive arthropathy (SEDT-PA)

This article introduces the hypothesis that mutant WISP3 (Wnt1 inducible secreted protein-3) triggers the phenotype shift of the chondrocytes, especially in the articular chondrocytes, by promoting sensitivity to IGF-1 (insulin-like growth factor 1), and results in chondrocytes apoptosis in SEDT-PA. SEDT-PA is also referred to as progressive pseudorheumatoid dysplasia (PPD), arthropathy progressive pseudorheumatoid of childhood (APPRC). Evidence for the hypothesis is based on the following indications: (1) SEDT-PA is caused by mutations of the WISP3 gene. WISP3 encodes a domain that bears homology to the amino-terminal domain of the insulin-like growth factor binding proteins (IGFBPs). (2) IGF-1 enhances chondrocyte hypertrophy by insulin-like actions. WISP3 can up-regulate the expression of type II collagen. When chondrocytes become hypertrophic, they reduce the expression of types II and IX collagen. (3) The chondrocytes in the normal articular cartilage maintain a stable phenotype. These cells exhibit no mitotic activity, low matrix synthesis and low degradation. But articular chondrocytes could react to certain stimuli such as IGF-1. (4) The loss of WISP3 expression alters the phenotype of the breast epithelium and promotes motility and invasion. The WISP3-deficient cells are extremely sensitive to the growth stimulatory effects of IGF-1. (5) The action of IGF-I is inhibited by IGFBPs, both in articular chondrocytes and in the normal breast epithelium. In conclusion, the mutant WISP3 lose is the function of inhibiting IGF-1 and disturbs the maintenance of a stable phenotype in articular chondrocytes. So, the articular chondrocytes undergo hypertrophic and terminal differentiation apoptosis. The precise mechanism of WISP3 function during postnatal cartilage growth and homeostasis is not clear yet. This hypothesis provides a new clue on the present mechanism study on SEDT-PA. If verified, this new concept may lead to a novel pathogenesis of SEDT-PA.

Glucocorticoid induced expression of connective tissue growth factor contributes to lactogenic differentiation of mouse mammary epithelial cells

The response of mammary epithelial cells to basement membrane and stroma induced signals contributes to the degree of differentiation in this tissue. The studies reported here indicate that connective tissue growth factor (CTGF) is highly elevated during lactogenic differentiation of the HC11 mouse mammary epithelial cell line. In addition, CTGF is expressed in the mouse mammary gland during pregnancy and lactation and it is expressed in primary mammary epithelial cell cultures established from pregnant mice. In HC11 cells CTGF is transcriptionally regulated by dexamethasone, but not by estrogen or progesterone, and CTGF expression is not dependent on TGFbeta. CTGF contributes to and is required for lactogenic differentiation of HC11 cells, as demonstrated by increased differentiation following expression of plasmid-encoded CTGF and decreased differentiation following depletion of endogenous CTGF with siRNA. Moreover, HC11 mouse mammary epithelial cells infected with an adenoviral vector encoding CTGF exhibit increased lactogenic differentiation. Plasmid vector-induced elevation of CTGF levels also increased the level of beta1 integrin in HC11 cells. Because the production of stromal factors is an important component of differentiation in mammary epithelial cells, the regulation of CTGF by glucocorticoids may play a critical role in this aspect of the control of differentiation. The studies reported here provide important information on the role of CTGF in mammary epithelial cell differentiation.

Suppression of Cell Proliferation and Signaling Transduction by Connective Tissue Growth Factor in Non–Small Cell Lung Cancer Cells

Connective tissue growth factor (CTGF) is a secreted protein that belongs to CCN family. The proteins in this family are implicated in various biological processes, such as angiogenesis, adhesion, migration, and apoptosis. In this study, we explored the roles of CTGF in lung tumorigenesis. The expression levels of CTGF in 58 lung cancer samples were reduced by >2 fold in 57% of the samples compared with matched normal samples using real-time reverse transcription-PCR. These results were confirmed by immunohistochemical staining for CTGF in normal lung epithelia and lung cancer. Cellular proliferation was inhibited in non-small cell lung cancer (NSCLC) cell lines NCI-H460, NCI-H520, NCI-H1299, and SK-MES-1 by CTGF overexpression. Partially purified CTGF suppressed lung cancer cell growth. The growth inhibition caused by CTGF overexpression was associated with growth arrest at G(0)-G(1) and prominent induction of p53 and ADP ribosylation factor. Most interestingly, overexpression of CTGF suppressed insulin-like growth factor-I-dependent Akt phosphorylation and epidermal growth factor-dependent extracellular signal-regulated kinase 1/2 phosphorylation. In summary, NSCLC cells expressed decreased levels of CTGF compared with normal lung cells; this lower expression has an effect on lung cancer cell proliferation and its cellular response to growth factors. Our data suggest that CTGF may behave as a secreted tumor suppressor protein in the normal lung, and its expression is suppressed in many NSCLCs.

Deletion of the COOH-terminal domain of CXC chemokine receptor 4 leads to the down-regulation of cell-to-cell contact, enhanced motility and proliferation in breast carcinoma cells

The CXC chemokine receptor 4 (CXCR4) contributes to the metastasis of human breast cancer cells. The CXCR4 COOH-terminal domain (CTD) seems to play a major role in regulating receptor desensitization and down-regulation. We expressed either wild-type CXCR4 (CXCR4-WT) or CTD-truncated CXCR4 (CXCR4-DeltaCTD) in MCF-7 human mammary carcinoma cells to determine whether the CTD is involved in CXCR4-modulated proliferation of mammary carcinoma cells. CXCR4-WT-transduced MCF-7 cells (MCF-7/CXCR4-WT cells) do not differ from vector-transduced MCF-7 control cells in morphology or growth rate. However, CXCR4-DeltaCTD-transduced MCF-7 cells (MCF-7/CXCR4-DeltaCTD cells) exhibit a higher growth rate and altered morphology, potentially indicating an epithelial-to-mesenchymal transition. Furthermore, extracellular signal-regulated kinase (ERK) activation and cell motility are increased in these cells. Ligand induces receptor association with beta-arrestin for both CXCR4-WT and CXCR4-DeltaCTD in these MCF-7 cells. Overexpressed CXCR4-WT localizes predominantly to the cell surface in unstimulated cells, whereas a significant portion of overexpressed CXCR4-DeltaCTD resides intracellularly in recycling endosomes. Analysis with human oligomicroarray, Western blot, and immunohistochemistry showed that E-cadherin and Zonula occludens are down-regulated in MCF-7/CXCR4-DeltaCTD cells. The array analysis also indicates that mesenchymal marker proteins and certain growth factor receptors are up-regulated in MCF-7/CXCR4-DeltaCTD cells. These observations suggest that (a) the overexpression of CXCR4-DeltaCTD leads to a gain-of-function of CXCR4-mediated signaling and (b) the CTD of CXCR4-WT may perform a feedback repressor function in this signaling pathway. These data will contribute to our understanding of how CXCR4-DeltaCTD may promote progression of breast tumors to metastatic lesions.

WISP-3 functions as a ligand and promotes superoxide dismutase activity

WISP-3 (Wnt1 inducible secreted protein-3) mutations have been linked to the connective tissue diseases progressive pseudorheumatoid dysplasia and polyarticular juvenile idiopathic arthritis, both of which are accompanied by disorders in cartilage maintenance/homeostasis. The molecular mechanism of WISP-3 mediated effects in the sustenance of cartilage has not been described in detail. Our previous study illustrates the potential role of WISP-3 in regulating the expression of cartilage-specific molecules that sustain chondrocyte growth and cartilage integrity. The present study was conducted to investigate the mode of action of WISP-3 in greater detail. Experimental results depicted here suggest that WISP-3 can function as a ligand and signal via autocrine and/or paracrine modes upon being secreted by chondrocytes. Furthermore, apart from regulating collagen II and aggrecan expression, WISP-3 may also promote superoxide dismutase expression and activity in chondrocytes.

Inhibition of CCN6 (WISP3) expression promotes neoplastic progression and enhances the effects of insulin-like growth factor-1 on breast epithelial cells

INTRODUCTION

CCN6/WISP3 belongs to the CCN (Cyr61, CTGF, Nov) family of genes that contains a conserved insulin-like growth factor (IGF) binding protein motif. CCN6 is a secreted protein lost in 80% of the aggressive inflammatory breast cancers, and can decrease mammary tumor growth in vitro and in vivo. We hypothesized that inhibition of CCN6 might result in the loss of a growth regulatory function that protects mammary epithelial cells from the tumorigenic effects of growth factors, particularly IGF-1.

METHOD

We treated human mammary epithelial (HME) cells with a CCN6 hairpin short interfering RNA.

RESULTS

CCN6-deficient cells showed increased motility and invasiveness, and developed features of epithelial-mesenchymal transition (EMT). Inhibition of CCN6 expression promoted anchorage-independent growth of HME cells and rendered them more responsive to the growth effects of IGF-1, which was coupled with the increased phosphorylation of IGF-1 receptor and insulin receptor substrate-1 (IRS-1).

CONCLUSION

Specific stable inhibition of CCN6 expression in HME cells induces EMT, promotes anchorage-independent growth, motility and invasiveness, and sensitizes mammary epithelial cells to the growth effects of IGF-1.

Identification of cell-of-origin breast tumor subtypes in inflammatory breast cancer by gene expression profiling

Inflammatory breast cancer (IBC) is an aggressive form of locally advanced breast cancer with high metastatic potential. Most patients have lymph node involvement at the time of diagnosis and 1/3 of the patients have distant metastases. In a previous study, we demonstrated that IBC is a distinct form of breast cancer in comparison with non-IBC. The aim of this study was to investigate the presence of the different molecular subtypes in our data set of 16 IBC and 18 non-IBC specimen. Therefore, we selected an 'intrinsic gene set' of 144 genes, present on our cDNA chips and common to the 'intrinsic gene set' described by Sorlie et al. [PNAS, 2003]. This set of genes was tested for performance in the Norway/Stanford data set by unsupervised hierarchical clustering. Expression centroids were then calculated for the core members of each of the five subclasses in the Norway/Stanford data set and used to classify our own specimens by calculating Spearman correlations between each sample and each centroid. We identified the same cell-of-origin subtypes in IBC as those already described in non-IBC. The classification was in good agreement with immunohistochemical data for estrogen receptor protein expression and cytokeratin 5/6 protein expression. Confirmation was done by an alternative unsupervised hierarchical clustering method. The robustness of this classification was assessed by an unsupervised hierarchical clustering with an alternative gene set of 141 genes related to the cell-of-origin subtypes, selected using a discriminating score and iterative random permutation testing. The contribution of the different cell-of-origin subtypes to the IBC phenotype was investigated by principal component analysis. Generally, the combined ErbB2-overexpressing and basal-like cluster was more expressed in IBC compared to non-IBC, whereas the combined luminal A, luminal B and normal-like cluster was more pronounced in non-IBC compared to IBC. The presence of the same molecular cell-of-origin subtypes in IBC as in non-IBC does not exclude the specific molecular nature of IBC, since gene lists that characterize IBC and non-IBC are entirely different from gene lists that define the different cell-of-origin subtypes, as evidenced by principal component analysis.