Breast Cancer Research - Latest Articles

PIK3CA mutation impact on survival in breast cancer patients and in ERalpha, PR and ERBB2-based subgroups

Magdalena Cizkova — 2012-02-13T00:00:00Z

IntroductionPIK3CA is the oncogene showing the highest frequency of gain-of-function mutations in breast cancer, but the prognostic value of PIK3CA mutation status is controversial. Methods: We investigated the prognostic significance of PIK3CA mutation status in a series of 452 patients with unilateral invasive primary breast cancer and known long-term outcome (median follow-up 10 years). Results: PIK3CA mutations were identified in 151 tumors (33.4%). The frequency of PIK3CA mutations differed markedly according to hormone receptor (ERalpha and PR) and ERBB2 status, ranging from 12.5% in the triple-negative subgroup (ER-/PR-/ERBB2-) to 41.1% in the HR+/ERBB2- subgroup. PIK3CA mutation was associated with significantly longer metastasis-free survival in the overall population (P=0.0056), and especially in the PR-positive and ERBB2-positive subgroups. In Cox multivariate regression analysis, the prognostic significance of PIK3CA mutation status persisted only in the ERBB2-positive subgroup. Conclusions: This study confirms the high prevalence of PIK3CA mutations in breast cancer. PIK3CA mutation is an emerging tumor marker which might become used in treatment-choosing process. The independent prognostic value of PIK3CA mutation status in ERBB2-positive breast cancer patients should be now confirmed in larger series of patients included in randomized prospective ERBB2-based clinical trials.

The growth response to androgen receptor signaling in ERalpha negative human breast cells is dependent on p21 and mediated by MAP kinase activation

Joe Garay — 2012-02-09T00:00:00Z

IntroductionAlthough a high frequency of androgen receptor (AR) expression in human breast cancers has been described, exploiting this knowledge for therapy has been challenging. This is in part because androgens can either inhibit or stimulate cell proliferation in preclinical models of breast cancer. In addition, many breast cancers co-express other steroid hormone receptors which can affect AR signaling, further obfuscating the effects of androgens on breast cancer cells. Methods: To create better defined models of AR signaling in human breast epithelial cells, we utilized estrogen receptor- a (ER) and progesterone receptor (PR) negative human breast cancerous and non-cancerous epithelial cell lines and engineered them to express AR thus allowing for the unambiguous study of AR signaling. We cloned a full length cDNA of human AR and expressed this transgene in MCF-10A non-tumorigenic human breast epithelial cells as well as MDA-MB-231 human breast cancer cells. We characterized the responses to AR ligand binding using various assays, and employed isogenic MCF-10A p21 "knock out" cell lines expressing AR to demonstrate the requirement of p21 in mediating the proliferative responses to AR signaling in human breast epithelial cells. Results: We show that hyperactivation of the MAP kinase pathway from both AR and epidermal growth factor receptor (EGFR) signaling results in a growth inhibitory response, whereas MAP kinase signaling from either AR or EGFR activation results in cellular proliferation. Additionally, p21 gene knock out studies demonstrate that AR signaling/activation of the MAP kinase pathway is dependent on p21. Conclusions: These studies present a new model for the analysis of AR signaling in human breast epithelial cells that lack ERa/PR expression, providing a system without the potential confounding effects of ERa/PR crosstalk. Using this system, we provide a mechanistic explanation for prior observations ascribing a dual role of AR signaling in human breast cancer cells. Since previous reports demonstrate that approximately 40% of breast cancers can lack p21 expression, our data also point out potential new caveats for exploiting AR as a target for breast cancer therapy.

Key signaling nodes in mammary gland development and cancer: Smad signal integration in epithelial cell plasticity

Anders Sundqvist — 2012-02-08T00:00:00Z

Smad proteins are the key intermediates of transforming growth factor-beta (TGF-β) signaling during development and in tissue homeostasis. Pertubations in TGF-β/Smad signaling have been implicated in cancer and other diseases. In the cell nucleus, Smad complexes trigger cell type- and context-specific transcriptional programs, thereby transmitting and integrating signals from a variety of ligands of the TGF-β superfamily and other stimuli in the cell microenvironment. The actual transcriptional and biological outcome of Smad activation critically depends on the genomic integrity and the modification state of genome and chromatin of the cell. The cytoplasmic and nuclear Smads can also modulate the activity of other signal transducers and enzymes such as microRNA-processing factors. In the case of breast cancer, the role of Smads in epithelial plasticity, tumor-stroma interactions, invasion, and metastasis seems of particular importance.

The role and function of cadherins in the mammary gland

Jennifer Andrews — 2012-02-08T00:00:00Z

Cadherins are transmembrane receptors that function through calcium-dependent homophilic and heterophilic interactions that provide cell-cell contact and communication in many different organ systems. In the mammary gland only a few of the cadherins that make up this large superfamily of proteins have been characterized. Frequently in metastatic breast cancer, the genes for cadherins are epigenetically silenced, mutated, or regulated differently. During epithelial-mesenchymal transition, cadherins that are expressed normally in the epithelial cells are down-regulated, while cadherins expressed in the mesenchyme are up-regulated. This process is known as cadherin switching, and its regulation can sometimes facilitate the increased motility, invasiveness and proliferation that occurs in metastatic cancer cells. Depending on the context, however, cell motility, invasiveness, proliferation and expression of mesenchymal markers can be independently modulated from cadherin expression, leading to partial epithelial-mesenchymal transitions and even mesenchymal-epithelial transitions (METs). This review will summarize the current understanding of cadherins found in the mammary gland and what is known about their mechanism of regulation in the mammary gland during normal physiological conditions and in breast cancer.

Progranulin (GP88) tumor tissue expression is associated with increased risk of recurrence in breast cancer patients diagnosed with estrogen receptor positive invasive ductal carcinoma.

Ginette Serrero — 2012-02-08T00:00:00Z

GP88 (progranulin) has been implicated in tumorigenesis and resistance to anti-estrogen therapies for estrogen receptor positive (ER+) breast cancer. Previous pathological studies showed that GP88 is expressed in invasive ductal carcinoma (IDC), but not in normal mammary epithelial tissue, benign lesions or lobular carcinoma. Based on these results, the present study examines GP88 prognostic significance in association with recurrence and death risks for ER+ IDC patients. Methods: Two retrospective multi-site clinical studies examined GP88 expression by immunohistochemistry (IHC) analysis of paraffin-embedded breast tumor tissue sections from ER+, IDC patients (lymph node positive and negative, stage 1 to 3) in correlation with patients' survival outcomes. The training study established a GP88 cut-off value associated with decreased disease-free (DFS) and overall (OS) survivals. The validation study verified the GP88 cut-off value and compared GP88 prognostic information with other prognostic factors, particularly tumor size, grade, disease stage and lymph node status in multivariate analysis. Results: GP88 expression is associated with a statistically significant increase in recurrence risk for ER+ IDC patients. The training study established that GP88 3+ score was associated with decreased DFS (p=0.0004) and OS (p=0.0036). The independent validation study verified that GP88 3+ score was associated with a 5.9-fold higher hazard of disease recurrence and a 2.5-fold higher mortality hazard compared to patients with tumor GP88<3+. GP88 remained an independent risk predictor after considering age, ethnicity, nodal status, tumor size, tumor grade, disease stage, progesterone receptor expression and treatments. Conclusions: The survival factor GP88 is a novel prognostic biomarker, predictive of recurrence risk and increased mortality for non metastatic ER+ IDC patients. Of importance, our data show that GP88 continues to be a prognostic factor even after 5 years. These results also provide evidence that GP88 provides prognostic information independent of tumor and clinical characteristics and would support prospective study to examine whether GP88 expression could help stratify patients with ER+ tumors for adjuvant therapy.

Initiating breast cancer by PIK3CA mutation

Todd Miller — 2012-02-07T00:00:00Z

PIK3CA mutations confer constitutive activation of PI3K, which initiates intracellular kinase signaling cascades that promote cell proliferation and survival. Recent studies by Meyer and colleagues, and Liu and colleagues demonstrate that expression of the H1047R exon 20 mutant of PIK3CA in luminal mammary epithelial cells induces tumorigenesis, implying that PIK3CA mutation is an early event in breast cancer. PIK3CA-H1047R-initiated tumors exhibit variable dependence on the oncogene and variable sensitivity to PI3K inhibition. Amplification of the oncogenes MYC and MET was observed in tumors that recurred following silencing of PIK3CA-H1047R, suggesting that these pathways represent mechanisms of escape from PI3K inhibition.

Breast cancer risk prediction and individualised screening based on common genetic variation and breast density measurement

Hatef Darabi — 2012-02-07T00:00:00Z

IntroductionOver the last decade several breast cancer risk alleles have been identified which has led to an increased interest in individualised risk prediction for clinical purposes. Methods: We investigate the performance of an up-to-date 18 breast cancer risk single-nucleotide polymorphisms (SNPs), together with mammographic percentage density (PD), body mass index (BMI) and clinical risk factors in predicting absolute risk of breast cancer, empirically, in a well characterised Swedish case-control study of postmenopausal women. We examined the efficiency of various prediction models at a population level for individualized screening by extending a recently proposed analytical approach for estimating number of cases captured. Results: The performance of a risk prediction model based on an initial set of seven breast cancer risk SNPs is improved by additionally including eleven more recently established breast cancer risk SNPs (P = 4.69 x 10-4). Adding mammographic PD, BMI and all 18 SNPs to a Swedish Gail model improved the discriminatory accuracy (the AUC statistic) from 55% to 62%. The net reclassification improvement was used to assess improvement in classification of women into low, intermediate, and high categories of 5-year risk (P = 8.93 x 10-9). For scenarios we considered, we estimated that an individualized screening strategy based on risk models incorporating clinical risk factors, mammographic density and SNPs, captures 10% more cases than a screening strategy using the same resources, based on age alone. Estimates of numbers of cases captured by screening stratified by age provide insight into how individualised screening programs might appear in practice. Conclusions: Taken together, genetic risk factors and mammographic density offer moderate improvements to clinical risk factor models for predicting breast cancer.

Germline DNA copy number variation in familial and early-onset breast cancer

Ana Krepischi — 2012-02-07T00:00:00Z

IntroductionGenetic factors for cancer predisposition remain elusive in the majority of patients with familial or clinical history suggestive of hereditary breast cancer. Germline DNA copy-number variation (CNV) has recently been implicated in predisposition to cancer such as neuroblastoma, prostate and colorectal. We evaluated the role of germline CNVs in breast cancer susceptibility, in particular those with low population frequencies (rare CNVs), which are more likely to impact disease. Methods: Using whole genome array-CGH, we screened a cohort of women fulfilling criteria for hereditary breast cancer, who did not carry BRCA1/BRCA2 mutations. Results: The median number of total and rare CNVs per genome were not different between controls and patients. However, a total of 26 rare germline CNVs were identified in 68 cancer patients, a proportion that was significantly different (P=0.0311) from the control group (23 rare CNVs in 100 individuals). Several of the genes affected by CNV variation in patients and controls had already been implicated in cancer. Conclusions: This is the first study to explore the contribution of germline CNVs to BRCA1/2 negative familial and early-onset breast cancer. The data suggest that rare CNVs may contribute to cancer predisposition in this small cohort of patients, and this trend needs to be confirmed in larger samples.

Contribution of CXCL12 secretion to invasion of breast cancer cells

Pamela Boimel — 2012-02-07T00:00:00Z

IntroductionNeu (HER2/ErbB2) is over-expressed in 25-30% of human breast cancer, correlating with a poor prognosis. Previous studies using the Neu transgenic mouse model (MMTV-Neu) demonstrated that the Neu-YB line had increased production of CXCL12 and increased metastasis, while the Neu-YD line had decreased metastasis. This study examines the role of increased production of CXCL12 in tumor cell invasion and malignancy. Methods: We studied invasion in the tumor microenvironment using multiphoton intravital imaging, in vivo invasion, and intravasation assays. CXCL12 signaling was altered by using the CXCR4 inhibitor AMD3100 or increasing CXCL12 expression. The role of macrophage signaling in vivo was determined using a colony stimulating factor-1 (CSF-1) receptor blocking antibody. Results: The Neu-YD strain was reduced in invasion, intravasation, and metastasis compared to the Neu-YB and Neu-NDL strains. Remarkably, for the Neu-YB strain, in vivo invasion to epidermal growth factor was dependent on both CXCL12/CXCR4 and CSF1/CSF1R signaling. Neu-YB tumors had increased macrophage and microvessel density. Over-expression of CXCL12 in MTLn3 cells increased in vivo invasion, as well as microvessel and macrophage densities. Conclusions: Expression of CXCL12 by tumor cells results in increased macrophage and microvessel density and in vivo invasiveness.

Small interfering RNA library screen identified polo-like kinase-1 (PLK1) as a potential therapeutic target for breast cancer that uniquely eliminates tumour-initiating cells

Kaiji Hu — 2012-02-06T00:00:00Z

IntroductionTriple negative breast cancers' (TNBCs) high rate of relapse is thought to be due to the presence of tumor-initiating cells (TICs), molecularly defined as being CD44high/CD24-/low. TICs are resilient to chemotherapy and radiation. However, there is no currently accepted molecular target against TNBC and moreover TICs. Therefore, we sought the identification of kinase targets that inhibit TNBC growth and eliminate TICs. Methods: A genome-wide human kinase siRNA library (691 kinases) was screened against the TNBC cell line SUM149 for growth inhibition. Selected siRNAs were then tested on four different breast cancer cell lines to confirm the spectrum of activity. Their effect on CD44high subpopulation and sorted CD44high/CD24-/low cells of SUM149 was also studied. Further studies were focused on polo-like kinase 1 (PLK1), including its expression in breast cancer cell lines, effect on CD44high/CD24-/low TIC subpopulation, growth inhibition, mammosphere formation and apoptosis as well as the activity of the PLK1 inhibitor, BI 2536. Results: 85 kinases were identified in the screen. 28 of them were further silenced by siRNAs on MDA-MB-231 (TNBC), BT474-M1 (ER+/HER2+, a metastatic variant) and HR5 (ER+/HER2+, a trastuzumab-resistant model) cells and showed broad spectrum of growth inhibition. Importantly, 12/28 kinases also reduced CD44high subpopulation compared to control in SUM149. Further tests of these 12 kinases directly on sorted CD44high/CD24-/low TIC subpopulation of SUM149 cells confirmed their effect. Blocking PLK1 had the greatest growth inhibition on breast cancer cells and TICs by ~80-90% after 72 hours. PLK1 was universally expressed in breast cancer cell lines representing all of the breast cancer subtypes, and was positively correlated to CD44. The PLK1 inhibitor BI 2536 showed similar effects on growth, mammosphere formation and apoptosis as PLK1 siRNAs. Finally, while paclitaxel, doxorubicin and 5-fluorouracil enriched CD44high/CD24-/low population compared to control in SUM149, subsequent treatment with BI 2536 killed the emergent population suggesting it could potentially be used to prevent relapse. Conclusion: Inhibiting PLK1 with siRNA or BI 2536 blocked growth of TNBCs including the CD44high/CD24-/low TIC subpopulation and mammosphere formation. Thus, PLK1 could be a potential therapeutic target for the treatment of TNBC as well as other subtypes of breast cancer.