Luminal Breast Tumors Research Articles

Comparison of BRCA1 Expression between Triple-Negative and Luminal Breast Tumors

Background:Previous studies have suggested that BRCA1 dysregulation has been shown to have a role in triple-negative phenotypic manifestation. However, differences of BRCA1 expression, as a tumor suppressor gene, have rarely been investigated between luminal and triple-negative breast tumors. Therefore, the present study attempted to compare the BRCA1 expression in triple-negative with luminal breast tumors and its association with the clinicopathologic characteristics of patients.Methods:BRCA1 expression was evaluated by real-time PCR in 26 triple-negative and 27 luminal breast tumors.Results:The results revealed that there is a high frequency of BRCA1 underexpression in both triple-negative and luminal breast tumors. The BRCA1 underexpression was related to young age at diagnosis, lymph node involvement, and grade III tumors.Conclusion:The observations suggest that decreased BRCA1 expression, regardless of tumor subtype, has a general role in breast malignancy and associated with poor prognostic features in breast tumors.

Posttranslationally modified progesterone receptors direct ligand-specific expression of breast cancer stem cell-associated gene programs

BackgroundEstrogen and progesterone are potent breast mitogens. In addition to steroid hormones, multiple signaling pathways input to estrogen receptor (ER) and progesterone receptor (PR) actions via posttranslational events. Protein kinases commonly activated in breast cancers phosphorylate steroid hormone receptors (SRs) and profoundly impact their activities.MethodsTo better understand the role of modified PRs in breast cancer, we measured total and phospho-Ser294 PRs in 209 human breast tumors represented on 2754 individual tissue spots within a tissue microarray and assayed the regulation of this site in human tumor explants cultured ex vivo. To complement this analysis, we assayed PR target gene regulation in T47D luminal breast cancer models following treatment with progestin (promegestone; R5020) and antiprogestins (mifepristone, onapristone, or aglepristone) in conditions under which the receptor is regulated by Lys388 SUMOylation (K388 intact) or is SUMO-deficient (via K388R mutation to mimic persistent Ser294 phosphorylation). Selected phospho-PR-driven target genes were validated by qRT-PCR and following RUNX2 shRNA knockdown in breast cancer cell lines. Primary and secondary mammosphere assays were performed to implicate phospho-Ser294 PRs, epidermal growth factor signaling, and RUNX2 in breast cancer stem cell biology.ResultsPhospho-Ser294 PR species were abundant in a majority (54%) of luminal breast tumors, and PR promoter selectivity was exquisitely sensitive to posttranslational modifications. Phospho-PR expression and target gene programs were significantly associated with invasive lobular carcinoma (ILC). Consistent with our finding that activated phospho-PRs undergo rapid ligand-dependent turnover, unique phospho-PR gene signatures were most prevalent in breast tumors clinically designated as PR-low to PR-null (luminal B) and included gene sets associated with cancer stem cell biology (HER2, PAX2, AHR, AR, RUNX). Validation studies demonstrated a requirement for RUNX2 in the regulation of selected phospho-PR target genes (SLC37A2). In vitro mammosphere formation assays support a role for phospho-Ser294-PRs via growth factor (EGF) signaling as well as RUNX2 as potent drivers of breast cancer stem cell fate.ConclusionsWe conclude that PR Ser294 phosphorylation is a common event in breast cancer progression that is required to maintain breast cancer stem cell fate, in part via cooperation with growth factor-initiated signaling pathways and key phospho-PR target genes including SLC37A2 and RUNX2. Clinical measurement of phosphorylated PRs should be considered a useful marker of breast tumor stem cell potential. Alternatively, unique phospho-PR target gene sets may provide useful tools with which to identify patients likely to respond to selective PR modulators that block PR Ser294 phosphorylation as part of rational combination (i.e., with antiestrogens) endocrine therapies designed to durably block breast cancer recurrence.

Mitotic read-out genes confer poor outcome in luminal A breast cancer tumors.

Luminal breast tumors have been classified into A and B subgroups, with the luminal A being associated with a more favorable clinical outcome. Unfortunately, luminal A tumors do not have a universally good prognosis. We used transcriptomic analyses using public datasets to evaluate the differential expression between normal breast tissue and breast cancer, focusing on upregulated genes included in cell cycle function. Association of selected genes with relapse free survival (RFS) and overall survival (OS) was performed using the KM Plotter Online Tool (http://www.kmplot.com). Seventy-seven genes were differentially expressed between normal and malignant breast tissue. Only five genes were associated with poor RFS and OS. The mitosis-related genes GTSE1, CDCA3, FAM83D and SMC4 were associated with poor outcome specifically in Luminal A tumors. The combination of FAM83D and CDCA3 for RFS and GTSE1 alone for OS showed the better prediction for clinical outcome. CDCA3 was amplified in 3.4% of the tumors, and FAM83D and SMC4 in 2.3% and 2.2%, respectively. In conclusion, we describe a set of genes that predict detrimental outcome in Luminal A tumors. These genes may have utility for stratification in trials of antimitotic agents or cytotoxic chemotherapy, or as candidates for direct target inhibition.

Abstract P2-05-25: Predictive value of ultra-high ESR1 mRNA expression in early breast cancer

Abstract Background Quantitative determination of estrogen receptor mRNA expression in luminal breast tumors is predictive for benefit from adjuvant tamoxifen compared to placebo treatment as has been shown in the large randomized NSABP B-14 trial, while protein determination by IHC or LBA is not (Kim et al JCO 2011). Interestingly, the ultrahigh expression of ESR1 mRNA (above ER score 10 by Oncotype test) has been indicative for tamoxifen benefit. This predictive cut-off value of mRNA expression is significantly higher than the diagnostic cut-off (at ER score 6.5). Here we tested wether the ultrahigh expression of ESR1 mRNA determined by commercial MammaTyper® testing is predictive for survival after neoadjuvant chemotherapy treatment of advanced breast cancer. Materials and Methods Pretreatment core cut biopsies from n=54 patients with PBC treated within a randomized phase II trial (2) of anthracyline/taxane based NAC with available clinical follow-up information were examined. RNA was extracted from the FFPE sections and ESR1 mRNA from each section was measured by commercial assays. For technical comparison of ESR1 mRNA values by Oncotype DX versus MammaTyper® from n=113 surgical samples were analyzed by both commercial assays in a blinded fashion. Statistical analysis was performed using the SAS JMP® 9.0.0 software. Results Quantification of ESR1 mRNA expression after RNA extraction from separate slices of 113 primary breast tumors and determination by different commercial RT-qPCR assays resulted in high correlation of continuous expression results (Spearman r=0,85; p<0,0001). The rate of ESR1 mRNA negative cases by both methods by predefined diagnostic cut-offs was low in this cohort (1/113 and 6/113, respectively) resulting in high concordance for positive ER status by both methods.The median expression of ER score and ESR1 40-DDCq was high (10,2 and 39,8, respectively) and almost exactly at the predictive ER score cut-off. Hence, the Tamoxifen benefit cut-off of ER score 10 by Oncotype is comparable with a 40-DDCqvalue of 39,6 for ESR1 mRNA determination by MammaTyper®, which resembles an ESR1 mRNA expression 3fold above the diagnostic cut-off. In the independent chemotherapy cohort theoptimal discrimination for overall survival could be achieved by an elevated ESR1 mRNA expression exactly at 39,6 resulting in 100% overall survival for ultra-high expressors and 75 % overall survival for lower ESR1 mRNA expression after 5 years (p=0,006). Conclusion Previous data suggest that ultrahigh expression of ESR1 mRNA is predictive for improved overall survival and tamoxifen benefit (1). Here we show that ultrahigh expression of ESR1 mRNA is also prognostic in more advanced breast tumors after neoadjuvant chemotherapy. These findings validate the importance of quantitative determination of estrogen receptor expression and substantiate the understanding of receptor expression being a continuous determinant with indication specific cut-off values. Ultrahigh expression of ESR1 seems to identify a distinct subset of luminal breast tumors with superior prognosis and benefit from tamoxifen treatment. These findings warrant further investigation, which are currently being done in independent large breast cancer cohorts. Citation Format: Wirtz RM, Scheffen I, Marme F, Laible M, Sclombs K, Schumacher C, Schneeweiss A, Eidt S, Sinn H-P. Predictive value of ultra-high ESR1 mRNA expression in early breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-05-25.

Abstract P4-06-02: The mammary ducts create a favourable microenvironment for xenografting of luminal and molecular apocrine breast tumours

Abstract This abstract was not presented at the symposium.

\u03b13 Chains of type V collagen regulate breast tumour growth via glypican-1

Pericellular α3(V) collagen can affect the functioning of cells, such as adipocytes and pancreatic β cells. Here we show that α3(V) chains are an abundant product of normal mammary gland basal cells, and that α3(V) ablation in a mouse mammary tumour model inhibits mammary tumour progression by reducing the proliferative potential of tumour cells. These effects are shown to be primarily cell autonomous, from loss of α3(V) chains normally produced by tumour cells, in which they affect growth by enhancing the ability of cell surface proteoglycan glypican-1 to act as a co-receptor for FGF2. Thus, a mechanism is presented for microenvironmental influence on tumour growth. α3(V) chains are produced in both basal-like and luminal human breast tumours, and its expression levels are tightly coupled with those of glypican-1 across breast cancer types. Evidence indicates α3(V) chains as potential targets for inhibiting tumour growth and as markers of oncogenic transformation.

Genetic and Epigenetic Regulation of TOX3 Expression in Breast Cancer.

Genome wide association studies (GWAS) have identified low penetrance and high frequency single nucleotide polymorphisms (SNPs) that contribute to genetic susceptibility of breast cancer. The SNPs at 16q12, close to the TOX3 and CASC16 genes, represent one of the susceptibility loci identified by GWAS, showing strong evidence for breast cancer association across various populations. To examine molecular mechanisms of TOX3 regulation in breast cancer, we investigated both genetic and epigenetic factors using cell lines and datasets derived from primary breast tumors available through The Cancer Genome Atlas (TCGA). TOX3 expression is highly up-regulated in luminal subtype tumors compared to normal breast tissues or basal-like tumors. Expression quantitative trait loci (eQTL) analyses revealed significant associations of rs3803662 and rs4784227 genotypes with TOX3 expression in breast tumors. Bisulfite sequencing of four CpG islands in the TOX3 promoter showed a clear difference between luminal and basal-like cancer cell lines. 5-Aza-2’-deoxycytidine treatment of a basal-like cancer cell line increased expression of TOX3. TCGA dataset verified significantly lower levels of methylation of the promoter in luminal breast tumors with an inverse correlation between methylation and expression of TOX3. Methylation QTL (mQTL) analyses showed a weak or no correlation of rs3803662 or rs4784227 with TOX3 promoter methylation in breast tumors, indicating an independent relationship between the genetic and epigenetic events. These data suggest a complex system of TOX3 regulation in breast tumors, driven by germline variants and somatic epigenetic modifications in a subtype specific manner.

Lgr6 labels a rare population of mammary gland progenitor cells that are able to originate luminal mammary tumours.

The mammary gland is composed of a complex cellular hierarchy with unusual postnatal plasticity. The identities of stem/progenitor cell populations, as well as tumour-initiating cells that give rise to breast cancer, are incompletely understood. Here we show that Lgr6 marks rare populations of cells in both basal and luminal mammary gland compartments in mice. Lineage tracing analysis showed that Lgr6+ cells are unipotent progenitors, which expand clonally during puberty but diminish in adulthood. In pregnancy or following stimulation with ovarian hormones, adult Lgr6+ cells regained proliferative potency and their progeny formed alveoli over repeated pregnancies. Oncogenic mutations in Lgr6+ cells resulted in expansion of luminal cells, culminating in mammary gland tumours. Conversely, depletion of Lgr6+ cells in the MMTV-PyMT model of mammary tumorigenesis significantly impaired tumour growth. Thus, Lgr6 marks mammary gland progenitor cells that can initiate tumours, and cells of luminal breast tumours required for efficient tumour maintenance.

The mammary ducts create a favourable microenvironment for xenografting of luminal and molecular apocrine breast tumours.

There is a paucity of models for hormone receptor-positive (HR+) breast cancer because of the difficulty of establishing xenografts from these tumours. We show that this obstacle can be overcome by injecting human tumour cells directly into the mammary ducts of immunodeficient mice. Tumours from 31 patients were infected overnight with a lentiviral vector expressing tdTomato and injected through the nipple into the mammary ducts of NOD-SCID-IL2RG-/- mice. Tumours formed in the mice in 77% of cases after the first injection (6/8 luminal A, 15/20 luminal B, and 3/3 molecular apocrine). Four luminal A and one molecular apocrine graft were tested in secondary and tertiary grafts: all were successfully passaged in secondary and 4/5 in tertiary grafts. None of the samples engrafted when injected subcutaneously. The morphology, oestrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR), and Ki-67 profiles of the clinical samples were maintained in the tertiary grafts. We also show that the intraductal approach can be used to test the response to targeted therapy with fulvestrant and palbociclib, using a genetically defined ER+ model. We conclude that the mammary ducts create a microenvironment that is uniquely favourable to the survival and growth of tumours derived from mammary hormone-sensing cells. This approach opens the door to testing genomically targeted treatment of HR+ tumours in precision medicine programmes. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Association between mesothelin expression and survival outcomes in patients with triple-negative breast cancer: a protocol for a systematic review.

BackgroundMesothelin is a membrane-bound glycoprotein. Although the biologic function of mesothelin is not very clear, researchers have found that it plays a role in the survival, proliferation, and migration of tumor cells. Identified as a tumor-associated biomarker, mesothelin is more often overexpressed in triple-negative breast cancer (TNBC) than in common luminal breast tumor subtype or normal tissues. The objective of this review is to determine the association between the expression of mesothelin and overall survival in patients with TNBC.Methods/designWe will search the following electronic databases: MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), PubMed, and Web of Science with no time or language restriction. Prospective or retrospective longitudinal studies that investigate mesothelin expression in TNBC or the prognosis of TNBC with mesothelin baseline measurement will be selected. Two reviewers will independently assess every abstract or full text for inclusion. Data on clinical outcomes, as well as on study design, research setting, study population, demographic characteristics of the participants, and methodological quality, will be extracted using a structured codebook developed by the authors. A pooled measure of associations will be assessed through meta-analyses if appropriate. Heterogeneity across the included studies will be evaluated using the I2 statistics. Findings will be reported according to the Meta-Analysis of Observational Studies in Epidemiology (MOOSE) guidelines and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The quality of evidence and risk of bias of the studies will be evaluated.DiscussionThe aim of this systematic review is to synthesize the evidence regarding the association between the expression of mesothelin and the survival outcomes of patients with TNBC. A better understanding of the expression frequency and prognostic value of mesothelin in TNBC will be essential to identifying a novel therapeutic target.Systematic review registrationPROSPERO CRD42016036212Electronic supplementary materialThe online version of this article (doi:10.1186/s13643-016-0313-6) contains supplementary material, which is available to authorized users.

LRG1 mRNA expression in breast cancer associates with PIK3CA genotype and with aromatase inhibitor therapy outcome

BackgroundPIK3CA is the most frequent somatic mutated oncogene in estrogen receptor (ER) positive breast cancer. We previously observed an association between PIK3CA genotype and aromatase inhibitors (AI) treatment outcome. This study now evaluates whether expression of mRNAs and miRs are linked to PIK3CA genotype and are independently related to AI therapy response in order to define potential expressed biomarkers for treatment outcome. Materials and methodsThe miR and mRNA expression levels were evaluated for their relationship with the PIK3CA genotype in two breast tumor datasets, i.e. 286 luminal cancers from the TCGA consortium and our set of 84 ER positive primary tumors of metastatic breast cancer patients who received first line AI. BRB Array tools class comparison was performed to define miRs and mRNAs whose expression associate with PIK3CA exon 9 and 20 status. Spearman correlations established miR–mRNA pairs and mRNAs with related expression. Next, a third dataset of 25 breast cancer patients receiving neo-adjuvant letrozole was evaluated, to compare expression levels of identified miRs and mRNAs in biopsies before and after treatment. Finally, to identify potential biomarkers miR and mRNA levels were related with overall survival (OS) and progression free survival (PFS) after first-line AI therapy. ResultsExpression of 3 miRs (miR-449a, miR-205-5p, miR-301a-3p) and 9 mRNAs (CCNO, FAM81B, LRG1, NEK10, PLCL1, PGR, SERPINA3, SORBS2, VTCN1) was related to the PIK3CA status in both datasets. All except miR-301a-3p had an increased expression in tumors with PIK3CA mutations. Validation in a publicly available dataset showed that LRG1, PGR, and SERPINA3 levels were decreased after neo-adjuvant AI-treatment. Six miR–mRNA pairs correlated significantly and stepdown analysis of all 12 factors revealed 3 mRNAs (PLCL1, LRG1, FAM81B) related to PFS. Further analyses showed LRG1 and PLCL1 expression to be unrelated with luminal subtype and to associate with OS and with PFS, the latter independent from traditional predictive factors. ConclusionWe showed in two datasets of ER positive and luminal breast tumors that the expression of 3 miRs and 9 mRNAs associate with the PIK3CA status. Expression of LRG1 is independent of luminal (A or B) subtype, decreased after neo-adjuvant AI-treatment, and is proposed as potential biomarker for AI therapy outcome.

Abstract 1656: Subtype-specific radiation response in human breast cancer and potential therapeutic effect of FAS death receptor modulation

Abstract Breast cancer is the most common malignancy diagnosed among women worldwide and represents a heterogeneous group of subtypes. Radiation therapy is an important component of multimodal treatment for women with breast cancer. However, little is known about radiation response among these subtypes. Recent clinical data suggests that distinct patterns of response to systemic therapy may exist in association with each phenotype. Therefore, understanding the intrinsic variation of radiation response in breast cancer subtypes is important in prescribing individualized radiotherapy that maximizes the therapeutic ratio. Our previous studies have identified marked changes in gene expression in breast patient tumors and breast tumor cell lines in response to radiation. Among candidate genes, FAS was consistently and significantly induced after radiation in luminal breast tumors and cell lines. Modulation of FAS in basal breast cancer cell lines favorably impacted radiation response. In this study, we further investigated the role of FAS modulation and radiation response in a mouse model of breast cancer. MCF7 (luminal), HCC1954 (HER2+) or SUM159 (basal) cells were implanted orthotopically into the dorsal mammary fat pad of nude mice. These mice were then treated with different doses of radiation. Our results showed that radiation treatment inhibited MCF7, and to a less extent HCC1954 tumor growth in a dose-dependent manner, while SUM159 tumors were resistant to radiation. The estimated TCD50 value was 19.30 Gy for MCF7 and 44.88 Gy for SUM159. FAS was induced in MCF7 tumors after radiation but showed no change in SUM159 tumors. To investigate whether FAS modulation can affect radiation response, we silenced FAS in MCF7 tumors and activated FAS in SUM159 tumors. We found that silencing of FAS did not negatively impact radiation response in MCF7 tumors, possibly due to compensation by other apoptotic pathways. On the other hand, FAS activating antibody in combination with radiation delayed SUM159 and HCC1954 tumor growth (p = NS). In conclusion, these results suggest that there is intrinsic variation in radiation response among breast cancer subtypes. FAS concurrent with radiation slows tumor growth in the radiation resistant subtypes, but the effect was not significant. Alternative subtype-specific modulators of radiation response are under investigation. Citation Format: Chen-Ting Lee, Yingchun Zhou, Kingshuk R. Choudhury, Sharareh Siamakpour Reihani, Mark W. Dewhirst, Janet K. Horton. Subtype-specific radiation response in human breast cancer and potential therapeutic effect of FAS death receptor modulation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1656.

Abstract 4591: Estrogen receptor-positive breast cancer: from genomic landscape to treatment approach

Abstract Background: Estrogen receptor (ER)-positive or luminal breast tumors represent around two-thirds of all breast cancers. Luminal breast cancer is a highly heterogeneous disease comprising different histologies, gene-expression profiles and mutational patterns, with very diverse clinical courses and responses to systemic treatment. Despite adjuvant endocrine therapy and chemotherapy treatment for patients at high risk of relapse, both early and late relapses still occur, a fact that highlights the unmet medical needs of these patients. A catalogue of molecular aberrations in ER+ breast cancer (BC) is critical for developing and deploying therapies that will improve patients’ lives. Methods: Comprehensive genomic profiling from 128 BC patients (February 2014 through October, 2015) were analyzed. Patients were biopsied after consultation and samples were characterized (ER, PR, and HER2 by IHC; FFPE samples for genomic [Foundation One] and proteomic analyses [Theranostics]). We also evaluated mutation distribution in cell free DNA via digital NGS using Guardant 360 panel. Results: Total 97 genes were altered in 83 ER+BC patients and most frequent genetic alterations are PIK3CA (40%), p53 (27.7%) and CCND1 (24%). The PI3K-AKT pathway specific genes (AK1, AKT2, PIK3CA, PIK3CB, PIK3R1, PTEN, MTOR, RICTOR, RAPTOR, TSC2, STK11, MDM2 and MDM4) were altered in 80% of patients. Analyzing the composite alterations in individual ER+BC patients, we observed that 20% of patients had alterations in two or more nodes of the PI3K pathway while alterations of cell cycle pathway genes (CCND1, CCNE1, CDK4, CDKN1B, CDKN2A/B and RB1) were observed in 36% of patients. Interestingly, concurrent alterations of both PI3K and cell cycle pathways were 24%. Hence we tested the anti-tumor efficacy of the combination of isoform-specific PI3K inhibitor (alpha or beta) and LEE011 using ER+ BC cell lines (PIK3CA mutated MCF7, T47D, & PTEN-null MDA-MB415 cells) based model. Data show a synergistic effect of PI3K alpha or beta inhibitor and CDK4/6 inhibitor as determined from the changes in proliferative and apoptotic signals as well as cell cycle arrest. Conclusion: Since a persistent expression of the CDK4-Cyclin D1 pathway activation enables tumor cells survival even in the presence of PI3K inhibitor (Cancer Cell 2014), results of our study demonstrated that the anti-tumor effect of isoform-specific PI3Ki and CDK4/6i be beneficial in RB wt ER+BC patients with a concurrent genetic alterations of these pathways. Citation Format: Pradip De, Casey Williams, Amy Krie, Kirstin Williams, Jessica Klein, Jennifer H. Carlson, Nandini Dey, Brian Leyland-Jones. Estrogen receptor-positive breast cancer: from genomic landscape to treatment approach. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4591.

Expression and methylation patterns partition luminal-A breast tumors into distinct prognostic subgroups.

BackgroundBreast cancer is a heterogeneous disease comprising several biologically different types, exhibiting diverse responses to treatment. In the past years, gene expression profiling has led to definition of several “intrinsic subtypes” of breast cancer (basal-like, HER2-enriched, luminal-A, luminal-B and normal-like), and microarray based predictors such as PAM50 have been developed. Despite their advantage over traditional histopathological classification, precise identification of breast cancer subtypes, especially within the largest and highly variable luminal-A class, remains a challenge. In this study, we revisited the molecular classification of breast tumors using both expression and methylation data obtained from The Cancer Genome Atlas (TCGA).MethodsUnsupervised clustering was applied on 1148 and 679 breast cancer samples using RNA-Seq and DNA methylation data, respectively. Clusters were evaluated using clinical information and by comparison to PAM50 subtypes. Differentially expressed genes and differentially methylated CpGs were tested for enrichment using various annotation sets. Survival analysis was conducted on the identified clusters using the log-rank test and Cox proportional hazards model.ResultsThe clusters in both expression and methylation datasets had only moderate agreement with PAM50 calls, while our partitioning of the luminal samples had better five-year prognostic value than the luminal-A/luminal-B assignment as called by PAM50. Our analysis partitioned the expression profiles of the luminal-A samples into two biologically distinct subgroups exhibiting differential expression of immune-related genes, with one subgroup carrying significantly higher risk for five-year recurrence. Analysis of the luminal-A samples using methylation data identified a cluster of patients with poorer survival, characterized by distinct hyper-methylation of developmental genes. Cox multivariate survival analysis confirmed the prognostic significance of the two partitions after adjustment for commonly used factors such as age and pathological stage.ConclusionsModern genomic datasets reveal large heterogeneity among luminal breast tumors. Our analysis of these data provides two prognostic gene sets that dissect and explain tumor variability within the luminal-A subgroup, thus, contributing to the advancement of subtype-specific diagnosis and treatment.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-016-0724-2) contains supplementary material, which is available to authorized users.

Predictive value of ultra-high ESR1 mRNA expression in early breast cancer.

e12045Background: Ultrahigh ESR1 mRNA expression in luminal breast tumors is predictive for benefit from adjuvant tamoxifen compared to placebo treatment in NSABP B14, while protein determination b...

Abstract IA28: Epigenetic heterogeneity in breast cancer

Abstract Heterogeneity of cancer cells between and within tumors is a major obstacle toward understanding and treatment of cancers. Variability of epigenetic states is one of the major contributor to both intertumor and intratumor heterogeneity. In breast cancer luminal and basal-like breast tumors have very different molecular and clinical profiles. However, even in individual tumors there is variability among cells for these features. The determinants of luminal cell phenotypes are fairly well understood and major transcriptional regulators have been identified. In contrast, transcriptional determinants of basal-like breast tumors are still poorly defined and high variability is observed among individual tumors. We have investigated molecular regulators of luminal and basal-like phenotypes by applying somatic cell genetics and cellular reprogramming approaches combined with comprehensive molecular profiling. We found that the basal-like state is predominantly dominant and it is defined mainly by epigenetic mechanisms. We have also identified candidate epigenetic and transcriptional regulators of basal-like cellular states. Modulation of epigenetic regulators may decrease intratumor heterogeneity and in combination with other agents could improve the efficacy of cancer therapies. Citation Format: Kornelia Polyak. Epigenetic heterogeneity in breast cancer. [abstract]. In: Proceedings of the AACR Special Conference: Developmental Biology and Cancer; Nov 30-Dec 3, 2015; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(4_Suppl):Abstract nr IA28.

Phorbol Myristate Acetate Suppresses Breast Cancer Cell Growth via Down‐regulation of P‐Rex1 Expression

Phosphatidylinositol‐3,4,5‐trisphosphate‐dependent Rac exchange factor 1 (P‐Rex1) is highly overexpressed in estrogen receptor‐positive and ErbB2‐overexpressing human luminal breast tumors. The present study was to investigate the role and mechanism underlying phorbol‐12‐myristate‐13‐acetate (PMA), a protein kinase C (PKC) activator, down‐regulation of P‐Rex1 in breast cancer cells. P‐Rex1 mRNA and protein expression were determined by real‐time PCR and western blot analysis, respectively. Cell growth was analyzed by counting cells number and 5‐bromo‐2′‐deoxyuridine (BrdU) cell proliferation assay. The translocation of PKC was examined by immunofluorescence staining. Our results showed that treatment with PMA caused a time‐ and concentration‐dependent decrease in P‐Rex1 protein levels in breast cancer MCF‐7 and BT‐474 cells with a maximum reduction of 87.2 ± 1.1 and 57.0 ± 8.6%, respectively, at a concentration of 10 ng/ml. Interestingly, either PMA treatment or silence of P‐Rex1 by siRNA inhibits MCF‐7 and BT‐474 cell growth by 60–80%, which can be attenuated by restoring P‐Rex1 expression. MCF‐7 and BT‐474 cells express PMA‐sensitive conventional (α and β) and novel (δ, ɛ and η) PKC isoforms. Immunofluorescence staining analysis of breast cancer cells showed translocation of PKCs from cytosol to the plasma membrane and/or nucleus, an indication of their activation upon PMA stimulation. The PKC general inhibitor Gö6983, but not the conventional PKC isoform inhibitor Gö6976, blocked PMA inhibition of P‐Rex1 expression and breast cancer cell growth. Expression of a constitutively active PKCɛ mutant suppressed P‐Rex1 expression and breast cancer cell growth, which was blocked by Gö6983 treatment. In contrast, expression of wild‐type PKCɛ, wild‐type or constitutively active PKCδ and PKCη had no effect. Together, our data suggest that PMA suppresses breast cancer cell growth via P‐Rex1 down‐regulation and PKCɛ activation plays a key role in this regulation. Our study may provide a novel strategy for development of chemotherapeutic agents for P‐Rex1‐overexpressing breast cancer patients that develop resistance to anti‐estrogen and/or anti‐ErbB2 therapies.Support or Funding InformationSupported by grants from NIH (5P20GM103489 and R01HL116849), Nebraska State LB595 research program and the National Natural Science Foundation of China (31100595 and 31300683).

Abstract A43: Context-dependent growth effects of progestins in estrogen receptor-positive breast cancer patient-derived xenografts (PDX)

Abstract Introduction: Progesterone (P4) and progesterone receptors (PR) play elusive roles in breast cancer. Synthetic progestins in hormone replacement therapy increase breast tumorigenesis, yet these same progestins at high doses can be an effective therapy for some advanced breast tumors. The literature supports that progestins can either stimulate or inhibit breast cancer cell growth, and an increasing body of evidence supports P4 promotes expansion of breast cancer stem cells. Interplay between PR and estrogen receptors (ER) is emerging as important in dictating growth and response to treatment. There is historical precedence for PR interference of ER dependent gene transcription; recent reports identify that PR modulate ER DNA binding events. Given the importance of PR as a biomarker and potential therapeutic target, and the uncertainty surrounding its context-dependent actions, we aimed resolve this using breast cancer PDX models. The purpose of this study was to evaluate the effects of natural and synthetic progestins on growth and estrogen-dependent gene expression in luminal breast tumors, and to define contexts that dictate their divergent effects. Experimental procedures: Six luminal breast cancer PDX developed at UCD-AMC were used for these studies. Most profiled as Luminal B subtype. Tumors generally fell into two types: a pure luminal phenotype and a mixed luminal/basal phenotype based on cytokeratin expression. Tumors varied in expression of ER, PR, and androgen receptors (AR) from low (<10% positive cells), moderate (30-50%), to high (>90%). Tumors were grown in vivo under conditions of continuous placebo, 17β-estradiol (estrogen), estrogen plus progesterone (P4), or estrogen plus the synthetic progestin medroxyprogesterone acetate (MPA) for several months and growth parameters monitored. Receptor content was measure by immunohistochemistry and western blots. Gene expression profiles of select tumors were determined using Affymetrix® GeneChip human gene microarrays and/or RNAseq and results analyzed using Partek Genomics Suite™ software, and Metacore™ pathway analysis. Summary: In two pure luminal PDX with high receptor levels (ER, PR, AR) both P4 and MPA significantly inhibited estrogen-dependent growth (growth-inhibited, GI). Two PDX (one pure luminal, one mixed) with moderate ER and low PR and AR showed no significant effect of P4 or MPA on estrogen-dependent growth (growth neutral, GN). One mixed luminal/basal PDX with low ER and PR and moderate AR showed no effect with P4, whereas MPA simulated tumor growth above that with estrogen alone (growth stimulated, GS). Study of one PDX is ongoing. In the GI tumors both P4 and MPA reversed expression of ~30% of estrogen regulated genes. In particular these tumors had high estrogen-dependent expression of the Notch pathway, which was blocked by both P4 and MPA. Progestins did not alter estrogen-dependent genes in the GN or GS tumors, which did not include the Notch pathway. MPA stimulated a unique set of genes in the GS tumor, and was able to mobilize AR to the nucleus whereas P4 did not. Conclusion: Progestins have mixed effects on breast cancer PDX tumor growth. Tumors that have high ER and PR and are highly estrogen-dependent are more likely to exhibit strong growth inhibition by progestins (both P4 and MPA). Tumors with mixed luminal/basal phenotype that have less ER and PR and are moderately estrogen-dependent are less likely to be progestin-inhibited. In tumors with low ER and PR but high AR content MPA can act as an AR agonist to stimulate growth. Tumor-specific downstream estrogen-dependent pathways such as Notch may indicate whether progestins are therapeutic. Additional tumors are needed to confirm these results with the long term goal of developing a molecular assay to define those tumors that may benefit from progestin treatment. Citation Format: Jessica Finlay-Schultz, Heather M. Brechbuhl, Rachel B. Rosen, Austin E. Gillen, Britta M. Jacobsen, Peter Kabos, Carol A. Sartorius. Context-dependent growth effects of progestins in estrogen receptor-positive breast cancer patient-derived xenografts (PDX). [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr A43.

Abstract B07: Mcl-1-mediated resistance to ABT-263 is combated by mTOR inhibition in luminal breast cancers

Abstract In the context of cancer, the intrinsic apoptotic pathway is exploited to favor tumor cell survival through overexpression of anti-apoptotic Bcl-2 family members (Bcl-A1, Bcl-2, Bcl-xL, Bcl-w and Mcl-1). We investigated targeting of anti-apoptotic Bcl-2 proteins in a panel of human luminal breast cancer cell lines. Use of ABT-263, the Bcl-2/Bcl-xL/Bcl-w inhibitor, induced transient tumor cell killing and decreased tumor cell growth in only 1 of 4 cell lines in three dimensional (3D) cultures. Mcl-1 expression and activity were rapidly upregulated upon ABT-263 treatment, highlighting the compensatory nature of Mcl-1. In luminal breast cancers, Mcl-1 was the most frequently amplified anti-apoptotic Bcl-2 family member according to The Cancer Genome Atlas, while nearly 80% of the luminal breast tumor epithelium was positive for Mcl-1 in a tissue microarray. Thus, we hypothesized that Mcl-1 may be a dominant tumor cell survival factor in luminal breast cancers. Use of the mTOR inhibitor RAD001 (everolimus) to target Mcl-1 indirectly decreased tumor cell growth and increased tumor cell killing in 3 of 4 cell lines, as well as WAP-Myc luminal mammary tumors, demonstrating the effectiveness of Mcl-1 as a therapeutic target in breast cancers. While Mcl-1 inhibition alone did not affect growth of T47D cells, robust growth inhibition and tumor cell killing were seen in all cell lines upon inhibition of Mcl-1 using RAD001 or a EIF4 complex inhibitor (4E1RCat) in combination with ABT-263, suggesting that the induction of Mcl-1 upon ABT-263 treatment may be supported by increased cap-dependent translation. These results demonstrate that the sensitivity of luminal breast cancers to ABT-263 is enhanced by Mcl-1 inhibition, warranting further investigation into inhibition of anti-apoptotic Bcl-2 family proteins, in particular Mcl-1, as a clinical strategy to improve survival of patients with luminal breast cancers. Citation Format: Michelle M. Williams, Linus Lee, Meghan M. Morrison, Courtney McKernan, Violeta Sanchez, Donna Hicks, Thomas Stricker, Rebecca S. Cook. Mcl-1-mediated resistance to ABT-263 is combated by mTOR inhibition in luminal breast cancers. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research; Oct 17-20, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(2_Suppl):Abstract nr B07.

Subtype-specific accumulation of intracellular zinc pools is associated with the malignant phenotype in breast cancer.

BackgroundZinc (Zn) hyper-accumulates in breast tumors and malignant cell lines compared to normal mammary epithelium. The mechanisms responsible for Zn accumulation and the consequence of Zn dysregulation are poorly understood.MethodsMicroarrays were performed to assess differences in the expression of Zn transporters and metallothioneins (MTs) in human breast tumors and breast cancer cell lines. Real-time PCR and immunoblotting were employed to profile Zn transporter expression in representative luminal (T47D), basal (MDA-MB-231), and non-malignant (MCF10A) cell lines. Zn distribution in human tumors was assessed by X-ray fluorescence imaging. Zn distribution and content in cell lines was measured using FluoZin-3 imaging, and quantification and atomic absorption spectroscopy. Functional consequences of ZnT2 over-expression in MDA-MB-231 cells including invasion, proliferation, and cell cycle were measured using Boyden chambers, MTT assays, and flow cytometry, respectively.ResultsGene expression profiling of human breast tumors and breast cancer cell lines identified subtype-specific dysregulation in the Zn transporting network. X-ray fluorescence imaging of breast tumor tissues revealed Zn hyper-accumulation at the margins of Luminal breast tumors while Zn was more evenly distributed within Basal tumors. While both T47D and MDA-MB-231 cells hyper-accumulated Zn relative to MCF10A cells, T47D cells accumulated 2.5-fold more Zn compared to MDA-MB-231 cells. FluoZin-3 imaging indicated that Zn was sequestered into numerous large vesicles in T47D cells, but was retained in the cytoplasm and found in fewer and larger, amorphous sub-cellular compartments in MDA-MB-231 cells. The differences in Zn localization mirrored the relative abundance of the Zn transporter ZnT2; T47D cells over-expressed ZnT2, whereas MDA-MB-231 cells did not express ZnT2 protein due to proteasomal degradation. To determine the functional relevance of the lack of ZnT2 in MDA-MB-231cells, cells were transfected to express ZnT2. ZnT2 over-expression led to Zn vesicularization, shifts in cell cycle, enhanced apoptosis, and reduced proliferation and invasion.ConclusionsThis comprehensive analysis of the Zn transporting network in malignant breast tumors and cell lines illustrates that distinct subtype-specific dysregulation of Zn management may underlie phenotypic characteristics of breast cancers such as grade, invasiveness, metastatic potential, and response to therapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0486-y) contains supplementary material, which is available to authorized users.