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Expression of RUNX1 Correlates with Poor Patient
Prognosis in Triple Negative Breast Cancer
Nicola Ferrari
1
, Zahra M. A. Mohammed
2¤
, Colin Nixon
1
, Susan M. Mason
1
, Elizabeth Mallon
3
,
Donald C. McMillan
2
, Joanna S. Morris
4
, Ewan R. Cameron
4
, Joanne Edwards
5
, Karen Blyth
1
*
1Transgenic Models Lab, Cancer Research UK Beatson Institute, Glasgow, Scotland, United Kingdom, 2Academic Unit of Surgery, College of Medical, Veterinary and Life
Sciences, University of Glasgow, Glasgow, Scotland, United Kingdom, 3University Pathology Unit, Southern General Hospital, Glasgow, Scotland, United Kingdom,
4School of Veterinary Medicine, University of Glasgow, Glasgow, Scotland, United Kingdom, 5Institute of Cancer Sciences, University of Glasgow, Glasgow, Scotland,
United Kingdom
Abstract
The RUNX1 transcription factor is widely recognised for its tumour suppressor effects in leukaemia. Recently a putative link
to breast cancer has started to emerge, however the function of RUNX1 in breast cancer is still unknown. To investigate if
RUNX1 expression was important to clinical outcome in primary breast tumours a tissue microarray (TMA) containing
biopsies from 483 patients with primary operable invasive ductal breast cancer was stained by immunohistochemistry.
RUNX1 was associated with progesterone receptor (PR)-positive tumours (P,0.05), more tumour CD4+(P,0.05) and CD8+
(P,0.01) T-lymphocytic infiltrate, increased tumour CD138+plasma cell (P,0.01) and more CD68+macrophage infiltrate (P,
0.001). RUNX1 expression did not influence outcome of oestrogen receptor (ER)-positive or HER2-positive disease, however
on univariate analysis a high RUNX1 protein was significantly associated with poorer cancer-specific survival in patients with
ER-negative (P,0.05) and with triple negative (TN) invasive breast cancer (P,0.05). Furthermore, multivariate Cox
regression analysis of cancer-specific survival showed a trend towards significance in ER-negative patients (P,0.1) and was
significant in triple negative patients (P,0.05). Of relevance, triple negative breast cancer currently lacks good biomarkers
and patients with this subtype do not benefit from the option of targeted therapy unlike patients with ER-positive or HER2-
positive disease. Using multivariate analysis RUNX1 was identified as an independent prognostic marker in the triple
negative subgroup. Overall, our study identifies RUNX1 as a new prognostic indicator correlating with poor prognosis
specifically in the triple negative subtype of human breast cancer.
Citation: Ferrari N, Mohammed ZMA, Nixon C, Mason SM, Mallon E, et al. (2014) Expression of RUNX1 Correlates with Poor Patient Prognosis in Triple Negative
Breast Cancer. PLOS ONE 9(6): e100759. doi:10.1371/journal.pone.0100759
Editor: Arto Mannermaa, University of Eastern Finland, Finland
Received February 24, 2014; Accepted May 28, 2014; Published June 26, 2014
Copyright: ß2014 Ferrari et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was funded by Cancer Research UK. The funders had no role in study design, data collection and analysis, decision to publish, or preparation
of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* Email: K.Blyth@beatson.gla.ac.uk
¤ Current address: University Department of Pathology, Omar Almukhtar University, Al bayda, Libya
Introduction
Breast cancer is the third most common cause of cancer death in
the UK, accountable for more than 11,000 deaths in 2011 alone
(www.cancerresearchuk.org) and an estimated 39,620 female
deaths in the USA in 2013 (www.cancer.gov). In human breast
cancer, oestrogen receptor (ER), progesterone receptor (PR), and
human epidermal growth factor receptor 2 (HER2) are well-
established prognostic and predictive markers, and testing for
them is now considered standard of care [1]. Based on the receptor
status, human breast cancer can be subdivided into three main
groups: oestrogen receptor positive (ER+), human epidermal
growth factor receptor 2 positive (HER2+) and triple negative
(ER2/PR2/HER2–). ER+and HER2+patients benefit from
targeted treatments such as Tamoxifen and/or Trastuzumab
which have consistently improved disease outcome [2]. On the
other hand, the triple negative (TN) subtype lacks any specific
targeted therapy and is associated with worse overall prognosis in
comparison with the other subtypes [3]. This underlines the urgent
need for new prognostic and therapeutic targets specific for this
group of patients.
The RUNX genes are a family of three transcription factors
(RUNX1, 2 and 3) known to play essential roles in haematopoiesis,
osteogenesis and neurogenesis [4]. Besides being key developmen-
tal regulators, RUNX genes are also important in cancer, acting
both as oncogenes or tumour suppressors in different systems [5].
RUNX1 is the most frequently mutated gene in human leukaemia
and many studies have focused on its tumour suppressive function
in haematopoietic malignancies [6]. However, in recent years, a
new role for RUNX1 outside the haematopoietic system has
started to emerge with several studies indicating how this
transcription factor could be more broadly implicated in cancer
[7,8]. In particular RUNX1 has been identified as a key regulator
of tumourigenesis in various epithelial cancers [9–11]. However
little is known about the role of RUNX1 in human breast cancer
[12]. Wang and colleagues using 3D culture models showed that
RUNX1 deletion in MCF10A acini resulted in increased cell
proliferation and abnormal morphogenesis [13]. In addition, three
independent large scale sequencing studies on human breast
PLOS ONE | www.plosone.org 1 June 2014 | Volume 9 | Issue 6 | e100759
cancers discovered recurrent RUNX1 mutations and deletions in
human tumours [14–16] while Kadota et al showed by qRT-PCR
on a small breast cancer cohort (29 samples) that RUNX1
downregulation is associated with high-grade primary breast
tumours [17]. Here we have carried out the first comprehensive
characterization of RUNX1 expression in tissues from a large
cohort of human breast cancers and demonstrate its prognostic
value in different tumour subtypes.
Materials and Methods
Patients
The expression studies in human tissues were ethically approved
from West of Scotland Research Ethics Service West of Scotland
REC4 (REC Ref: Project Number 02/SG007(10), R and D
project: RN07PA001). Consent was not obtained, but all patient
information is anonymised with all patient identifiers removed.
Patients diagnosed with invasive breast cancer at three Glasgow
hospitals (Royal Infirmary, Western Infirmary and Stobhill
Figure 1. Expression of RUNX1 in human breast cancer cell lines. RUNX1 expression by western blot on a panel of human breast cancer cell
lines with basal–like (HCC-70, BT-549, BT-20, MDA-MB-231, MDA-MB-436, MDA-MB-468) and luminal-like (BT-474, MCF-7, T47D, MDA-MB-361)
features. HDAC2 used as a loading control. hMEC-TERT; immortalized human mammary epithelial cells.
doi:10.1371/journal.pone.0100759.g001
Table 1. Clinico-pathological characteristics of patients with primary operable invasive ductal breast cancer.
Clinico-pathological characteristics (total) Patients (n%)
Age (#50/.50 years) (n= 483) 141 (29%)/342 (71%)
Size (#20/21–50/.50 mm) (n= 481) 280 (58%)/186 (39%)/15 (3%)
Tumour type (Special type/lobular/ductal) (n = 483) 23 (5%)/33 (7%)/427 (88%)
Grade (I/II/III) (n = 481) 88 (18%)/202 (42%)/191 (40%)
Involved lymph node (Negative/positive) (n = 478) 268 (56%)/210 (44%)
Oestrogen -receptor status (ER2/ER+) (n = 481) 184 (38%)/297 (62%)
Progesterone -receptor status (PR2/PR+) (n = 480) 266 (55%)/214 (45%)
HER2 status (HER22/HER2+) (n = 466) 393 (84%)/73 (16%)
Lymphovascular invasion (Absent/present) (n = 372) 198 (53%)/174 (47%)
Microvessel density (CD34+) (Low/medium/high) (n = 450) 157 (35%)/150 (33%)/143 (32%)
Ki-67 status (Low Ki-67/high Ki-67) (n= 468) 353 (75%)/115 (25%)
Tumour necrosis (Absent/present) (n = 473) 213 (45%)/260 (55%)
TUNEL (Low/high) (n = 417) 235 (56%)/182 (44%)
General inflammatory infiltrate (Low high) (n = 473) 334 (71%)/139 (29%)
Tumour CD4+T- lymphocytic infiltrate (Low/medium/high) (n = 474) 217 (46%)/93 (20%)/164 (34%)
Tumour CD8+T- lymphocytic infiltrate (Low/medium/high) (n = 474) 162 (34%)/154 (32.5%)/158 (33%)
Tumour CD138+B- lymphocytic infiltrate (Low/medium/high) (n = 473) 265 (56%)/60 (13%)/148 (31%)
Tumour CD68+macrophages infiltrate (Low/medium/high) (n = 471) 141 (30%)/164 (35%)/166 (35%)
Loco-regional treatment (Lumpectomy+radiotherapy/mastectomy+radiotherapy) (n = 483) 170 (35%)/313 (65%)
Systemic treatment (ER-based treatment) (hormonal/hormonal+chemotherapy/chemotherapy/none) (n =476) 252 (53%)/98 (20%)/103 (22%)/23 (5%)
RUNX1 (Negative/positive) (n = 483) 117 (24%)/366 (76%)
(n = 483).
doi:10.1371/journal.pone.0100759.t001
RUNX1 in Triple Negative Breast Cancer
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Hospital) between 1995 and 1998 were studied (n = 483). Clinical
and pathological data including age, histological tumour type,
grade, tumour size, lymph node status, lymphovascular invasion,
type of surgery and use of adjuvant treatment (chemotherapy,
hormonal therapy and radiotherapy) were retrieved from the
patient records and histopathology reports.
Tissue microarray (TMA) construction and
immunohistochemistry
Tissue microarrays (TMA) were already available for use in this
study. 0.6 mm
2
cores of breast cancer tissue, identified by the
pathologist (EM), were removed from representative areas of the
tumour taken from breast cancer patients at the time of surgical
resection. All tissue microarray blocks were constructed in
triplicate and were utilized to assess ER, PR, HER2 status, Ki-
67 and microvessel density by immunohistochemical analyses as
previously described [18–21]. Immunohistochemistry was used to
quantify cellular infiltrate of macrophages [19], CD4+, CD8+
lymphocytes and CD138+plasma cells as previously reported [22].
Immunohistochemistry for RUNX1. RUNX1 antibody
(Sigma, HPA004176) was validated to confirm its specificity by
western blot (Figure S1). Expression was detected in a positive
control (T6i) but not in a leukaemia cell line deleted for RUNX1
(3SS cells). Human mammary epithelial cells (hMEC) transfected
with a RUNX1 overexpression vector (hMEC-RUNX1) or empty
vector (hMEC-Puro) were used as an independent validation.
TMAs were stained for RUNX1 by immunohistochemistry. Heat
induced epitope retrieval for RUNX1 was performed at 98uC for
25 minutes in citrate buffer (pH 6). Endogenous peroxidase was
blocked by incubation in 3% hydrogen peroxide (DAKO, UK) for
5 minutes. The cores were then incubated with primary antibody
for RUNX1 added at dilution of 1:100 for 40 minutes at 25uC.
Sites of binding were detected using the appropriate Envision
secondary antibody (DAKO code K4003) and visualized using
DAB (3-39diaminobenzidine, DAKO, UK) according to the
manufacturer’s instruction. Cores were counterstained with
haematoxylin, dehydrated and coverslipped with DPX.
Weighted histoscore method. RUNX1 staining was quan-
tified using the weighted histoscore method to give a value of 0–
300 [23]. One hundred and fifty cores (10% of total core number)
were scored independently for epithelial RUNX1 expression by
two observers (NF and ZM) blind to patient’s outcome and the
other observer’s score. Interclass Correlation Coefficient (ICC),
measure of inter-observer agreement, was 0.82. NF then scored all
cores and this data was used in subsequent analysis.
Statistical analysis
Inter-relationships between variables were assessed using
contingency tables with the chi-squared test for trend as
appropriate. Univariate analysis and multivariate survival analysis
with calculation of hazard ratios (HR) were performed using Cox’s
proportional-hazards model. A stepwise backward procedure was
used to derive a final model of the variables that had a significant
independent relationship with survival. Mortality incidences up to
March 2010 were included in the analysis. Analysis was performed
using SPSS software version 19 (SPSS Inc., Chicago, IL, USA).
Table 2. The relationship between RUNX1 and clinico-pathological characteristics of patients with primary operable invasive
ductal breast cancer.
Clinico-pathological characteristics (total)
RUNX1 Negative
(n = 117)
RUNX1 Positive
(n = 366) p-value
Age (#50/.50 years) (n = 483) 25/92 116/250 0.033
Size (#20/21–50/.50 mm) (n = 481) 70/43/4 210/143/11 0.769
Tumour type (Special type/lobular/ductal) (n = 483) 8/9/100 15/24/327 0.197
Grade (I/II/III) (n = 481) 17/57/43 71/145/148 0.891
Involved lymph node (Negative/positive) (n = 478) 70/46 198/164 0.287
Oestrogen -receptor status (ER2/ER+) (n = 481) 53/64 131/233 0.072
Progesterone -receptor status (PR2/PR+) (n = 480) 75/42 191/172 0.03
HER2 status (HER22/HER2+) (n = 466) 97/16 296/57 0.613
Lymphovascular invasion (Absent/present) (n = 372) 48/36 150/138 0.414
Microvessel density (CD34+) (Low/medium/high) (n = 450) 44/31/30 113/119/113 0.143
Ki-67 status (Low Ki-67/high Ki-67) (n = 468) 87/26 266/89 0.658
Tumour necrosis (Absent/present) (n = 473) 52/63 161/197 0.963
TUNEL (Low/high) (n = 417) 51/42 184/140 0.738
General inflammatory infiltrate (Low high) (n = 473) 81/34 253/105 0.962
Tumour CD4+T- lymphocytic infiltrate (Low/medium/high) (n = 474) 63/22/30 154/71/134 0.015
Tumour CD8+T- lymphocytic infiltrate (Low/medium/high) (n = 474) 55/28/32 107/126/126 0.004
Tumour CD138+B- lymphocytic infiltrate (Low/medium/high) (n = 473) 80/11/24 185/49/124 0.001
Tumour CD68+macrophages infiltrate (Low/medium/high) (n = 471) 50/39/24 91/125/142
,
0.001
Loco-regional treatment (Lumpectomy+radiotherapy/mastectomy+radiotherapy) (n = 483) 39/78 131/235 0.628
Systemic treatment (ER-based treatment) (hormonal/hormonal+chemotherapy/chemotherapy/none)
(n = 476)
65/23/21/6 187/75/82/17 0.42
Cancer specific survival (months)* 156 (146–165) 149 (143–155) 0.158
*Mean (95%CI).
doi:10.1371/journal.pone.0100759.t002
RUNX1 in Triple Negative Breast Cancer
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Cell lines
T6i leukaemia cell line overexpressing RUNX1 [24] and 3SS (a
cell line generated from a murine lymphoma which is genetically
deleted for RUNX1 and kindly provided by Gillian Borland in
ERC’s lab) were used respectively as positive and negative controls
in RUNX1 western blots. The genetically altered mouse used to
generate 3SS was covered by University of Glasgow ethical review
process and project licence PPL60/4408. hMEC-TERT cell line
[25] (a kind gift of Barbara Chaneton) was grown in HuMEC
complete media (Gibco). MDA-MB-231, MDA-MB-436, MDA-
MB-468, HCC-70, BT-20, BT-549, T47D, MDA-MB-361, MCF-
7 and BT-474 were originally sourced from the American Type
Culture Collection (ATCC). All cell lines were grown in a Galaxy+
incubator (RS Biotech) at 37uC with 5% CO
2
.
To generate RUNX1 overexpressing cells, hMEC-TERT were
transfected with pBABE-Puro-RUNX1 or pBABE-Puro (kindly
provided by Dr Anna Kilbey) through electroporation using
Nucleofector Kit V, program T-013 (Amaxa, Lonza). After
electroporation, cells were allowed to recover for 24 h and then
selected in puromycin selection media (10 mg/ml) for 2 weeks.
Western blot
Nuclear extracts were prepared from mammary cell lines using
NE-PER Nuclear and Cytoplasmic Extraction Reagents (Thermo
Scientific, Cat No 78833) as per kit instructions. Protein extracts
were resolved on 10% NuPAGE Novex Bis-Tris gels (Life
Technologies) and transferred to Hybond-ECL nitrocellulose
membranes (Amersham). Membranes were probed with antibod-
ies to RUNX1 (HPA004176, Sigma), HDAC2 (sc-6296, Santa
Cruz) and GAPDH (Cell Signalling).
Results
Characterisation of RUNX1 expression in human breast
cancer
RUNX1 expression was first tested on a panel of breast cancer
cell lines. The chosen cell lines included normal human mammary
epithelial cells derived from primary tissue and immortalised with
TERT expression (hMEC-TERT), 6 basal-like (HCC-70, BT-549,
BT-20, MDA-MB-231, MDA-MB-436, MDA-MB-468) and 4
luminal-like (BT-474, MCF-7, T47D, MDA-MB-361) breast
cancer cell lines. Significantly, RUNX1 expression was not
detectable in normal hMEC-TERT but was expressed in all
breast cancer cell lines tested with the exception of BT-549
(Figure 1). These results suggest that RUNX1 expression could be
dysregulated in human breast cancer.
To investigate if RUNX1 expression influenced clinical
outcome in primary breast tumours, a tissue microarray (TMA)
containing biopsies from 483 patients with operable invasive
ductal breast cancer [18] was stained for RUNX1. Baseline
clinico-pathological characteristics of the patients included in the
TMA are shown in Table 1. The invasive cancers showed different
degrees of RUNX1 expression, predominantly localized to the
nucleus (Figure 2A). RUNX1 expression in the tumour epithelium
was determined by histoscore which takes into account the
percentage of positive signal and staining intensity. Patients were
divided into two groups: RUNX1 negative (histoscore = 0,
n = 117) and RUNX1 positive (histoscore .0, n = 366). The
relationships between RUNX1 expression and clinico-pathological
characteristics in patients with primary operable ductal invasive
breast cancer are shown in Table 2. In the whole cohort a number
of factors were identified to be associated with positive RUNX1
Table 3. The relationship between RUNX1 and clinico-pathological characteristics of patients with triple negative primary
operable invasive ductal breast cancer.
Clinico-pathological characteristics (total) RUNX1 Negative RUNX1 Positive
p-
value
Age (#50/.50 years) (n = 483) 10/22 33/53 0.477
Size (#20/21–50/.50 mm) (n = 481) 17/15/0 43/38/4 0.537
Tumour type (Special type/lobular/ductal) (n = 483) 5/0/27 6/2/78 0.223
Grade (I/II/III) (n = 481) 0/9/23 4/14/66 0.857
Involved lymph node (Negative/positive) (n = 478) 20/12 48/38 0.515
Lymphovascular invasion (Absent/present) (n = 372) 16/9 37/35 0.278
Microvessel density (CD34+) (Low/medium/high) (n = 450) 8/11/11 30/17/37 0.928
Ki-67 status (Low Ki-67/high Ki-67) (n = 468) 22/9 69/16 0.239
Tumour necrosis (Absent/present) (n = 473) 7/25 16/70 0.691
TUNEL (Low/high) (n = 417) 14/8 48/17 0.363
General inflammatory infiltrate (Low high) (n = 473) 10/22 40/46 0.137
Tumour CD4+T- lymphocytic infiltrate (Low/medium/high) (n = 474) 18/3/10 25/17/42 0.016
Tumour CD8+T- lymphocytic infiltrate (Low/medium/high) (n = 474) 11/7/13 28/16/40 0.675
Tumour CD138+B- lymphocytic infiltrate (Low/medium/high) (n = 473) 19/3/9 42/8/34 0.251
Tumour CD68+macrophages infiltrate
(Low/medium/high) (n = 471)
14/7/10 36/17/31 0.71
Loco-regional treatment (Lumpectomy+radiotherapy/mastectomy+radiotherapy) (n = 483) 16/16 35/51 0.367
Systemic treatment (ER-based treatment) (hormonal/hormonal+chemotherapy/chemotherapy/none) (n = 476) 8/7/14/2 21/8/46/9 0.356
Cancer specific survival (months)* 163 (148–179) 129 (114–144) 0.013
*Mean (95%CI).
(n = 118).
doi:10.1371/journal.pone.0100759.t003
RUNX1 in Triple Negative Breast Cancer
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protein levels including age (P,0.05), ER status (P,0.10), PR
status (P,0.05), tumour lymphocyte and macrophage infiltrate (all
P,0.05). In contrast, in those patients with triple negative receptor
status only the tumour CD4 lymphocytic infiltrate was significantly
associated with positive RUNX1 protein levels (Table 3; P,0.05).
The relationship between RUNX1 expression and clinical
outcome was then assessed by looking at cancer-specific survival in
the full cohort as shown in Figure 2B. Survival analyses showed no
significant difference between RUNX1 negative (mean of 156
months - 95% confidence interval, 146–165 months) and RUNX1
positive tumours (mean of 149 months - 95% confidence interval,
143–155 months) (Figure 2B). Minimum follow-up was 142
months; the median follow-up of the survivors was 164 months.
110 patients developed recurrence; 18 local, 71 distant, 6 with
both and 15 with no information available. During the follow up
period, 207 patients died and of these, 95 deaths could be directly
attributed to their disease.
Impact of RUNX1 expression on survival in breast cancer
according to hormonal status
To define the prognostic impact of RUNX1 expression in
different breast cancer subtypes, the patient cohort was divided
into 4 subgroups accordingly to their receptor status (ER+, ER–,
HER2+and ER2/PR2/HER22). The distribution of RUNX1
positive and negative samples in relation to hormonal status (ER/
PR/HER2) of the full cohort is shown in Table S1. No specific
enrichment of RUNX1 was detected in any one of the hormonally
defined subgroups, similar to what has been shown at a
transcriptomic level [26]. The relationship between RUNX1
expression and clinical outcome was then assessed by looking at
cancer-specific survival in each breast cancer subtype. Survival
analyses showed no difference between the RUNX1 positive and
negative groups in the ER+and HER2+patients (Figure 3A, 3C).
However, RUNX1 showed a positive association with worse
prognosis in the ER2(Figure 3B) and in the triple negative (TN)
(Figure 3D) patients. In the TN subgroup mean cancer-specific
survival of RUNX1 positive patients was 129 months (95% CI,
114–144 months) compared to 163 months (95% CI, 148–179
months) of the RUNX1 negative group. The relationships between
RUNX1 and clinico-pathological characteristics were examined in
patients with ER– (Table S2) and TN tumours (Table 3). In
addition to a significant increase in CD4+T-lymphocytic infiltrate
(P,0.05), RUNX1 positive tumours showed a significant increase
in CD138+B- lymphocytic infiltrate (P,0.05) in ER- patients
(Table S2). In a univariate analysis the presence of RUNX1 was
associated with poorer cancer-specific survival for patients with
ER- tumours (Table 4, p,0.05) and showed a tendency towards
significance as an independent prognostic marker in multivariate
Figure 2. RUNX1 expression and cancer-specific survival in primary operable breast cancer. (A) Representative examples of invasive
breast carcinomas in a tissue microarray containing 483 breast cancers which were positive (left) and negative (right) for RUNX1 expression. Note the
nuclear staining in the tumour epithelium. Scale bar represents 100 mm. (B) The association between the absence and the presence of RUNX1 and
cancer-specific survival in primary operable breast cancer (n = 483). Survival curves are plotted for patients with cancers scored positive for RUNX1
(solid line), or negative for RUNX1 expression (dotted line). P.0.1, P-value calculated using Log Rank (Mantel-Cox) test.
doi:10.1371/journal.pone.0100759.g002
RUNX1 in Triple Negative Breast Cancer
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Table 4. The relationship between clinic-pathological characteristics of patients with ER- negative primary operable invasive ductal breast cancer and recurrence-free/cancer-
specific survival.
Recurrence-free survival Cancer-specific survival
Univariate
survival analysis
Multivariate
survival analysis
Univariate
survival analysis
Multivariate
survival analysis
Clinico-pathological
characteristics (total)
Hazard ratio
(95% CI)
P
-value
Hazard ratio
(95% CI)
P
-value
Hazard ratio
(95% CI)
P
-value
Hazard ratio
(95% CI)
P
-value
Age (#50/.50 years) 0.79 (0.45–1.38) 0.401 1.02 (0.57–1.83) 0.948
Size (#20/21–50/.50 mm) 2.01 (1.20–3.38) 0.008 1.98 (1.18–3.33) 0.01 2.02 (1.20–3.40) 0.008 1.81 (1.04–3.13) 0.035
Tumour type (Special type/lobular/ductal) 2.26 (0.81–6.36) 0.121 3.48 (0.78–15.56) 0.103
Grade (I/II/III) 1.10 (0.69–1.74) 0.701 1.71 (0.94–3.11) 0.077 0.435
Involved lymph node (Negative/positive) 1.91 (1.07–3.39) 0.027 0.108 2.83 (1.54–5.21) 0.001 2.24 (1.19–4.24) 0.013
RUNX1 (Negative/positive) 1.77 (0.88–3.54) 0.108 2.29 (1.07–4.88) 0.033 2.09 (0.97–4.48) 0.058
doi:10.1371/journal.pone.0100759.t004
Table 5. The relationship between clinic-pathological characteristics of patients with triple negative primary operable invasive ductal breast cancer and recurrence-free/cancer-
specific survival.
Recurrence-free survival Cancer-specific survival
Univariate
survival analysis
Multivariate
survival analysis
Univariate
survival analysis
Multivariate
survival analysis
Clinico-pathological
characteristics (total)
Hazard ratio
(95% CI)
P
-value
Hazard ratio
(95% CI)
P
-value
Hazard ratio
(95% CI)
P
-value
Hazard ratio
(95% CI)
P
-value
Age (#50/.50 years) 0.95 (0.44–2.04) 0.888 1.18 (0.57–2.46) 0.659
Size (#20/21–50/.50 mm) 2.53 (1.23–5.21) 0.012 2.31 (1.14–4.65) 0.019 2.76 (1.45–5.25) 0.002 2.63 (1.36–5.09) 0.004
Tumour type (Special type/lobular/ductal) 5.33 (0.36–78.77) 0.223 3.18 (0.73–13.83) 0.122
Grade (I/II/III) 0.97 (0.49–1.93) 0.926 1.40 (0.64–3.07) 0.404
Involved lymph node (Negative/positive) 2.48 (1.15–5.35) 0.021 2.19 (1.00–4.81) 0.05 4.15 (1.91–9.02) ,0.001 4.01 (1.83–8.81) 0.001
RUNX1 (Negative/positive) 3.40 (1.02–11.28) 0.046 3.00 (0.90–10.05) 0.075 4.03 (1.23–13.27) 0.022 3.83 (1.16–12.67) 0.028
doi:10.1371/journal.pone.0100759.t005
RUNX1 in Triple Negative Breast Cancer
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analysis (p = 0.058). More interestingly, RUNX1 was significantly
associated with poorer recurrence-free survival and cancer-specific
survival for patients with triple negative disease (Table 5, p = 0.046
and p = 0.022 respectively). Using multivariate analysis RUNX1
expression was an independent prognostic marker for cancer
specific-survival in the TN subtype when assessed against
established pathological prognostic factors such as tumour size,
grade, tumour type and lymph node status (Table 5).
Discussion
Recent studies have highlighted a novel link for RUNX1 with
breast cancer [13–16] but to date no direct assessment of RUNX1
protein has been carried out. We have now addressed this need
and show that 366/483 (76%) of invasive breast carcinomas in a
tumour tissue microarray were positive for RUNX1 protein. Our
analysis reveals that there was no difference in overall survival of
the full patient cohort, or in ER+,PR+and HER2+subgroups,
when stratified on RUNX1 expression. However on univariate
analysis, positive RUNX1 expression was significantly associated
with poorer cancer-specific survival in the ER2(P,0.05) and
triple negative (ER2/PR2/HER22)(P,0.05) groups of patients.
There was also a trend towards significance on multivariate Cox
regression analysis of cancer-specific survival in ER2breast
cancer (P,0.10) which reached significance in triple negative
breast cancer (TNBC) (P,0.05). TNBC, which accounts for 15%
to 20% of breast cancers, is an aggressive disease, associated with a
significantly higher probability of relapse and poorer overall
survival when compared with other breast cancer subtypes [27].
The lack of identified molecular targets in the majority of TNBCs
means that chemotherapy remains the treatment of choice for
these patients and unfortunately early relapse after chemotherapy
is common [28]. Hence there is an urgent need for identification of
better prognostic markers and novel therapeutic targets for this
subtype [3,29]. Only a few markers have so far been identified as
having a predictive role for the prognosis of TNBC patients
Figure 3. RUNX1 expression and cancer-specific survival in different subtypes of breast cancer. The association between the absence
and the presence of RUNX1 and cancer-specific survival in patients with (A) ER-positive, (B) ER-negative, (C) HER2-positive and (D) triple negative (TN)
primary operable breast cancer. Survival is plotted for patients with cancers positive for RUNX1 (solid line), or those with no RUNX1 expression
(dotted line). ER+cohort (n = 297), p = 0.974; ER– (n = 184), p = 0.028; HER2+cohort (n = 73), p = 0.406; TN cohort (n = 118), p = 0.013. P-values
calculated using Log Rank (Mantel-Cox) test.
doi:10.1371/journal.pone.0100759.g003
RUNX1 in Triple Negative Breast Cancer
PLOS ONE | www.plosone.org 7 June 2014 | Volume 9 | Issue 6 | e100759
[30,31]. Our results now suggest the utility of RUNX1 as a novel
biomarker. In fact, regression analysis using the Cox’s propor-
tional Hazards model confirmed that RUNX1 has prognostic
value together with tumour size and lymph node status in the
TNBC subgroup. Furthermore, multivariate analysis indicated
that RUNX1 expression was independent of the established
pathological prognostic factors currently used in the clinic making
it a new putative prognostic indicator for TN tumours.
It is intriguing that even though RUNX1 was expressed in most
breast cancer cell lines (Figure 1) and the majority of patients
(Table S1) regardless of hormonal status, it was only in the
hormone-negative patients that RUNX1 expression correlated
with patient outcome. Our data therefore indicate that TNBCs
expressing RUNX1 represent a group of tumours with the poorest
prognosis and suggest that in this subtype RUNX1 may be
contributing to tumour progression. If RUNX1 has a pro-
oncogenic role in TNBCs, the question arises as to why this effect
is not observed in tumours expressing the oestrogen receptor. It is
possible that this is being masked by the capacity of RUNX1 to
attenuate or distort ER signalling [26]. In this scenario RUNX1
would be exerting opposing effects; dampening ER driven growth
yet inducing latent tumour aggression. These results may explain
why in a recent flurry of papers ascribing a tumour suppressor role
for RUNX1 in breast cancer [12–16], mutations were found
almost exclusively in ER+cancers. Of course it will be important
to definitively establish a pro-oncogenic role for RUNX1 in
TNBC and understand why expression is maintained in the most
aggressive subtype. Interestingly our data are supported by several
transcriptomic studies that have identified RUNX1 as a possible
oncogene in TNBC [32–34]. In particular RUNX1 is among a 264
gene signature which correlates with a poor prognosis in TNBC
[33] whilst another study demonstrated an inverse correlation
between RUNX1 expression and survival in the claudin low group
of TNBCs [32]. RUNX1 was also among the top 20% differentially
expressed genes in two TN subtypes identified by cluster analysis,
namely the ‘mesenchymal stem-like’ (MSL), and ‘luminal andro-
gen receptor’ (LAR) subtypes [34]. The MSL subtype also displays
low expression of claudins 3, 4, and 7, supporting a possible link
between RUNX1 expression and the claudin-low subtype.
Inflammation has been shown to represent a critical component
of tumour progression [35]. Of significance, RUNX1 expression
correlates with the presence of lymphocytic CD4+infiltrate in
TNBC. RUNX1 is one of the key factors that drives various
aspects of T-cell differentiation including regulation of cytokine
production [36]. We could speculate that in TNBC highly positive
for RUNX1, that RUNX1 would drive a transcriptional
programme in breast cancer cells resulting in production and
secretion of high levels of cytokines which would then lead to
recruitment of lymphocytic cells at the tumour site. Further studies
will clarify the significance of the correlation between RUNX1
and CD4 lymphocytes in TNBC.
The widespread expression of RUNX1 in TNBC also suggests
new therapeutic avenues for the treatment of TNBCs; for example
the development of small-molecule inhibitors which bind to CBFb
and inhibit RUNX1 activity opens the possibility of a RUNX1-
specific targeted therapy [37,38]. In addition, work from
Tumbar’s laboratory has shown that RUNX1 overexpression
leads to STAT3 activation and is necessary for skin and oral
cancer growth [39]. STAT3 is involved in human breast cancer
with high STAT3 levels correlating with poorer survival [40]. If
further studies can establish if RUNX1 overexpression and
STAT3 activation are conserved in human breast cancer, and in
TNBC in particular, this could pave the way for new treatment
options based on the use of STAT3 inhibitors. Taken together our
results identify RUNX1 as a new biomarker in TNBC and are
opening exciting possibilities for the development of novel targeted
therapies for this subgroup.
Supporting Information
Figure S1 Validation of the RUNX1 antibody. RUNX1
antibody specificity was confirmed by western blot using known
positive (T6i, hMEC-RUNX1) and negative (3SS, hMEC-Puro)
controls. GAPDH used as a loading control. T6i; leukaemia cell
line overexpressing RUNX1. 3SS; leukaemia cell line deleted for
RUNX1. hMEC-TERT (immortalized human mammary epithe-
lial cells) transfected with RUNX1 (hMEC-RUNX1) or empty
vector (hMEC-Puro).
(TIF)
Table S1 Distribution of RUNX1 expression in relation to
breast cancer hormonal status.
(DOCX)
Table S2 The relationship between RUNX1 and clinico-
pathological characteristics of ER- patients with primary operable
invasive ductal breast cancer (n = 184).
(DOCX)
Acknowledgments
The authors wish to thank Barbara Chaneton, Anna Kilbey and Gillian
Borland for the kind gifts of cell lines and vectors. We thank Catherine
Winchester for critical reading of the manuscript. The image analysis
system used in the study was gifted by the Think Pink charity and Western
Infirmary Breast Endowment Fund.
Author Contributions
Conceived and designed the experiments: NF EC JE KB. Performed the
experiments: NF ZM CN SM. Analyzed the data: NF ZM EM DM JM EC
JE KB. Contributed reagents/materials/analysis tools: ZM EM DM JE.
Wrote the paper: NF ZM JE KB.
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