van Schooneveld et al. Breast Cancer Research (2015) 17:21 DOI 10.1186/s13058-015-0526-y REVIEW Open Access Dysregulation of microRNAs in breast cancer and their potential role as prognostic and predictive biomarkers in patient management Eleni van Schooneveld1*, Hans Wildiers1, Ignace Vergote1, Peter B Vermeulen2, Luc Y Dirix2 and Steven J Van Laere1,2 Abstract MicroRNAs (miRNAs) are an emerging class of gene expression modulators with relevant roles in several biological processes, including cell differentiation, development, apoptosis, and regulation of the cell cycle. Deregulation of those tiny RNA molecules has been described frequently as a major determinant for the initiation and progression of diseases, including cancer. Not only miRNAs but also the enzymes responsible for miRNA processing could be deregulated in cancer. In this review, we address the role of miRNAs in the pathogenesis of breast cancer, since there are oncogenic, tumor-suppressive, and metastatic-influencing miRNAs. Additionally, the different detection platforms and normalization strategies for miRNAs will be discussed. The major part of this review, however, will focus on the capability of miRNAs to act as diagnostic, predictive, or prognostic biomarkers. We will give an overview of their potential to correlate with response to or benefit from a given treatment and we will consider their ability to give information on prognosis in breast cancer. We will focus on miRNAs validated by more than one study or verified in independent cohorts or where results rely on preclinical as well as clinical evidence. As such, we will discuss their potential use in the personalized management of breast cancer. Introduction MicroRNAs Breast cancer and breast cancer heterogeneity MicroRNAs (miRNAs) are a group of small non-coding Breast cancer is the most frequent carcinoma and sec- RNAs able to regulate gene expression at the post- ond most common cause of cancer-related mortality in transcriptional level by binding to the 3′ untranslated women [1]. Its heterogeneous character is reflected in region (UTR) of target mRNAs. This leads to cleavage of the classification into four intrinsic subtypes (luminal A, the target mRNA by the Ago2 ribonuclease in the RNA- luminal B, basal-like, and ErbB2+), a normal-like group, induced silencing complex (RISC) or inhibition of trans- and a new subtype, referred to as claudin-low. Histologi- lation [3]. Alternatively, miRNAs can exert their effect cally, breast cancer can be divided into in situ and inva- by modulating the relationship between effector and tar- sive carcinoma, both of which can be further subdivided get mRNAs rather than acting as regulators of particular into ductal and lobular. Stratification by integrative mRNAs [4]. Deregulation of miRNA expression and clustering is based on genomic and transcriptomic data potential altered gene expression may contribute to the [2]. Curtis and colleagues [2] revealed new biological development of cancerous phenotypes [5]. Several stud- subgroups as integrative clusters, characterized by well- ies showed a differential miRNA expression profile in defined copy number alterations, gene expression, and cancer as compared with normal, and a global miRNA distinct clinical outcomes. downregulation was a common trait of human malig- nancies [6,7]. Materials and methods * Correspondence: [email protected] Relevant published articles were searched on PubMed 1Department of Oncology, University Hospitals Leuven and Catholic University Leuven, Herestraat 49, Leuven B-3000, Belgium databases from 2001 to present by using the following Full list of author information is available at the end of the article © 2015 van Schooneveld et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. van Schooneveld et al. Breast Cancer Research (2015) 17:21 Page 2 of 15 search criteria to retrieve articles and abstracts: (micro- the most prominent miRNAs involved in the pathogen- RNA* or miR*) AND (breast cancer); depending on the esis of breast cancer is depicted in Tables 1 and 2. chapter discussed in the review, we complemented this with AND (diagnostic OR prognostic OR predictive). Oncogenic microRNAs and ‘metastamiRs’ We focused on recent publications or findings vali- Examples of breast oncomirs are miR-10b, miR-21, miR- dated by several independent studies. Studies were con- 155, miR-373, and miR-520c. (See Table 1 and list of sidered eligible on the basis of the following inclusion abbreviations for miRNA targets.) OncomiRs exert their criteria: (i) miRNAs were evaluated in breast cancer cells oncogenic activity by targeting tumor-suppressor genes or samples (blood or tissue) derived from patients with and activating oncogenic transcription factors [8,15]. breast cancer, including publically available breast cancer MiR-10b targets HOXD10, thereby promoting cell mi- cohorts; (ii) the relationship between the studied miR- gration and invasion [8,16,17]. miR-21 has been reported NAs and breast cancer biology was investigated, or (iii) to be associated with invasive and metastatic breast cancer the relationship between miRNAs and outcome or ther- [18] and regulates epithelial-to-mesenchymal transition apy response in breast cancer was examined. Articles (EMT) and HIF1A in breast cancer stem cell-like cells were excluded if they met one of the following criteria: [19]. It also inhibits various tumor-suppressor proteins (i) published articles were retracted articles or comments; [20-22]. MiR-155 suppresses SOCS1 both in vivo and (ii) lack of key information on breast cancer biology, prog- in vitro [23], and upregulation results in proliferation of nosis, or prediction of therapy response; and (iii) manu- MCF7 cells [24]. FOXO3 was identified as another miR- scripts reported on cancer types other than breast cancer. 155 target, whose inhibition leads to enhanced cell sur- vival and tumor growth [25]. The expression of miR-373 MicroRNAs and breast cancer and -520c, which target CD44, is associated with metasta- The role of microRNAs in breast cancer biology and sis, invasion, and migration [26,27]. metastasis In cancer, miRNAs play a role in oncogenesis, metastasis, Tumor-suppressive and metastasis-suppressive microRNAs and resistance to various therapies and can be classified as Tumor-suppressor miRNAs exhibit a lower expression in oncogenes (oncomirs) or tumor-suppressor genes [8-10]. cancer cells and suppress oncogene expression, thereby Additionally, both pro-metastatic (‘metastamiRs’)and controlling cellular differentiation [28]. In regard to the metastasis-suppressor miRNAs can be identified [11,12]. global downregulation of miRNAs in cancer, it is worth Many miRNA genes are located in genomic regions mentioning that the majority of miRNAs have a tumor- involved in chromosomal alterations. Chromosomal re- suppressive function, some of which exhibit anti-metastatic gions encompassing oncogenic miRNAs may be ampli- properties as well. (See Table 2 and list of abbreviations for fied, resulting in increased expression of the oncomir. miRNA targets). Tumor-suppressive miRNAs could reside in fragile sites MiR-125b, which targets erythropoietin (EPO) and its characterized by deletions or mutations, leading to re- receptor (EPOR) as well as ERBB2, is found to be one of duced levels of these miRNAs [13,14]. An overview of the most downregulated miRNAs in breast cancer [29-31]. Table 1 List of major oncogenic microRNAs in breast cancer miRNA Target Function Number of samplesa Reference miR-10b HOXD10 Promotes cell migration, invasion and metastasis n = 23 [8,16,17] miR-21 PDCD4, HIF1A Promotes invasion, metastasis, migration and EMT Cell culture study [18,19,22] TPM1, PTEN, PDCD4 Promotes invasion n = 17 [20] TIMP3 Promotes invasion n = 32 [21] miR-155 SOCS1 Promotes cell growth and proliferation n = 15 [23] TP53INP1 Promotes proliferation Cell culture study [24] FOXO3 Promotes proliferation and survival n = 115 [25] miR-373 CD44 Promotes cell migration and invasion n = 11 [26] Promotes invasion and metastasis Cell culture study [27] miR-520c CD44 Promotes cell migration, invasion and metastasis n = 11 [26] MetastamiRs are indicated in bold. aWhen applying more than one reference, we focused on the study with the most relevant number of investigated patient samples. The other studies serve as validation and confirm the results. EMT, epithelial-to-mesenchymal transition; FOXO3, forkhead box protein O3; HIF1A, hypoxia-inducible factor-1α; HOXD10, homeobox D10; miRNA, microRNA; PDCD4, programmed cell death protein 4; PTEN, phosphatase and tensin homolog; SOCS1, suppressor of cytokine signaling 1; TIMP3, metalloproteinase inhibitor 3; TM1, tropomyosine 1; TP53INP, tumor protein p53 inducible nuclear protein. van Schooneveld et al. Breast Cancer Research (2015) 17:21 Page 3 of 15 Table 2 List of major tumor suppressive microRNAs in breast cancer miRNA Target Function Number of samplesa Reference miR-125b EPO, EPOR Inhibits cell proliferation and differentiation n = 42 [29] ENPEP, CK2-α,CCNJ, MEGF9 Inhibits cell proliferation n = 25 [30] ERBB2 Inhibits migration and invasion