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124 | CANCER DISCOVERY�FEBRUARY 2015 www.aacrjournals.org
REVIEW
Synovial Sarcoma: Recent Discoveries as a Roadmap to New Avenues for Therapy Torsten O. Nielsen 1 , Neal M. Poulin 1 , and Marc Ladanyi 2
1 Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada. 2 Department of Pathology and Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, New York.
Corresponding Author: Marc Ladanyi, Molecular Diagnostics Service, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10065. Phone: 212-639-6369; Fax: 212-717-3515; E-mail: ladanyim@mskcc.org
doi: 10.1158/2159-8290.CD-14-1246
©2015 American Association for Cancer Research.
ABSTRACT Oncogenesis in synovial sarcoma is driven by the chromosomal translocation t(X,18;
p11,q11), which generates an in-frame fusion of the SWI/SNF subunit SS18 to the
C-terminal repression domains of SSX1 or SSX2. Proteomic studies have identifi ed an integral role of
SS18–SSX in the SWI/SNF complex, and provide new evidence for mistargeting of polycomb repression
in synovial sarcoma. Two recent in vivo studies are highlighted, providing additional support for the
importance of WNT signaling in synovial sarcoma: One used a conditional mouse model in which knock-
out of β-catenin prevents tumor formation, and the other used a small-molecule inhibitor of β-catenin
in xenograft models.
Signifi cance: Synovial sarcoma appears to arise from still poorly characterized immature mesenchymal
progenitor cells through the action of its primary oncogenic driver, the SS18–SSX fusion gene, which
encodes a multifaceted disruptor of epigenetic control. The effects of SS18–SSX on polycomb-mediated
gene repression and SWI/SNF chromatin remodeling have recently come into focus and may offer new
insights into the basic function of these processes. A central role for deregulation of WNT–β-catenin sig-
naling in synovial sarcoma has also been strengthened by recent in vivo studies. These new insights into
the the biology of synovial sarcoma are guiding novel preclinical and clinical studies in this aggressive
cancer. Cancer Discov; 5(2); 124–34. ©2015 AACR.
CLINICAL FEATURES Synovial sarcoma is an aggressive neoplasm that accounts
for 10% to 20% of soft-tissue sarcomas in the adolescent
and young adult population ( 1 ). Although it is typically
diagnosed in young adults (median age 35), the age range is
between 5 and 85 years ( 2 ). There is a slight male predeliction
(M:F ratio 1.13); 70% of cases present in the extremities, and
the most common pattern of metastatic spread is to the lung
( 3 ). The mainstay of treatment is wide surgical excision with
adjuvant or neoadjuvant radiotherapy, which provides a good
chance of cure for localized disease. However, the disease is
prone to early and late recurrences, and 10-year disease-free
survival remains on the order of 50% ( 3 ). Synovial sarcoma is
moderately sensitive to cytotoxic chemotherapy with agents
such as ifosfamide and anthracyclines ( 4, 5 ).
THE SS18 – SSX FUSION ONCOGENE Synovial sarcoma is uniquely characterized by the balanced
chromosomal translocation t(X,18; p11,q11), demonstrable
in virtually all cases ( 2 ), not found in any other human neo-
plasms. This translocation creates an in-frame fusion of the
SS18 gene to SSX1 or SSX2 ( 6 ), whereby all but the carboxy
terminal (C-terminal) 8 amino acids of SS18 become fused
to the C-terminal 78 amino acids of the SSX partner ( Fig. 1 ).
An analogous translocation of SSX4 is detected in less than
1% of cases ( 7 ).
Multiple lines of evidence implicate SS18 – SSX as the cen-
tral genetic “driver” in this cancer: (i) its presence as the sole
cytogenetic anomaly in up to a third of cases ( 8 ), (ii) the low
frequency of additional mutations ( 9 ), (iii) its preservation
in metastatic and advanced lesions ( 8 ), (iv) the death of
synovial sarcoma cells upon SS18 – SSX knockdown ( 10 ), and
(v) its ability to induce tumors in conditional mouse models
with appropriate histology, gene expression, and immu-
nophenotype with 100% penetrance ( 11 ).
Functional Studies of SS18–SSX Initial functional studies of SS18–SSX used yeast two
hybrids and GAL4 fusion constructs, in which the relevant
protein domains are fused to the DNA-binding domain of
GAL4. These studies showed that SS18 is a transcriptional
coactivator and that C-terminal SSX domains mediate repres-
sion ( 12, 13 ). The fusion oncoprotein thus contains both
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Advances in Synovial Sarcoma REVIEW
activating and repressing domains, although neither partner
has a DNA-binding domain. Several other putative bind-
ing partners were also identifi ed as shown in Fig. 1 , but the
mechanisms targeting the fusion protein to specifi c DNA
regions were elusive until recently.
SS18 and SS18–SSX Incorporate into the SWI/SNF Complex
Thaete and colleagues ( 14 ) showed association of both
SS18 and SS18–SSX with the DNA-dependent ATPase BRM,
the catalytic subunit of SWI/SNF chromatin remodeling
complexes. Subsequently, Kato and colleagues ( 15 ) showed
that SS18 is a stable and integral component of SWI/SNF
complexes using coimmunoprecipitation and mass spectros-
copy in nuclear extracts of HeLa cells.
Middeljans and colleagues ( 16 ) extended these results
by showing that the fusion oncoprotein is similarly incor-
porated into stable SWI/SNF complexes. All commonly
observed subunits were recovered in reciprocal purifi cations
between tandem affi nity purifi cation-tagged SS18–SSX1 and
other subunits, indicating minimal perturbation of the core
complex when the fusion oncogene is stably expressed in
HEK293 cells. Kadoch and Crabtree ( 17 ) observed high-
affi nity binding of both SS18 and SS18–SSX to the core sub-
units of SWI/SNF, and immunodepletion of nuclear extracts
showed undetectable levels outside of this association. In
contrast with the results of Middeljans and colleagues ( 16 ),
these authors observed that expression of the fusion onco-
gene induced depletion of the BAF47 (SMARCB1) subunit
from the SWI/SNF complex in experiments using transiently
expressed GFP-tagged SS18–SSX in an HEK293 background.
The authors also reported SMARCB1 loss in synovial sar-
coma cell lines, noting that siRNA knockdown of SS18–SSX
restored SMARCB1 inclusion in SWI/SNF complexes.
Both studies suggest that SMARCB1’s association with
SWI/SNF may be more labile than for other subunits, and
it is conceivable that SMARCB1 is displaced from SWI/SNF
by aberrant protein interactions involving SS18–SSX. Alter-
nately, SMARCB1 may be stabilized in SWI/SNF complexes
by unknown binding partners in different experimental con-
ditions (e.g., transduced vs. transfected HEK293 cells, or dif-
ferences in the parent HEK293 cell lines, which have complex
genomes and known clonal heterogeneity). HEK293 cells,
although convenient for transfection and at least partially
permissive for (short-term) SS18–SSX expression, may not
represent the most relevant cell line model as discussed in
the Cellular Background for SS18–SSX Oncogenesis section,
below. Resolution of these confl icting results will have impor-
tant implications because SMARCB1 (aka SNF5, INI1) is a
known tumor suppressor, with homozygous loss in 98% of
rhabdoid tumors ( 18 ), 90% of epithelioid sarcomas, and more
than half of myoepithelial carcinomas ( 19 ). If SMARCB1 loss
contributes to oncogenesis in synovial sarcoma, advances in
the study of SWI/SNF–directed therapies in rhabdoid tumors
may have direct translational implications. Of potential
importance, synthetic lethalities may be explored by analogy
to rhabdoid tumors, where, for example, tumorigenesis was
found to depend on functional BRG1 in the residual SWI/
SNF complex ( 20 ). Although caution is currently indicated
in drawing simple parallels with rhabdoid tumors, these
proteomic studies imply that the mechanisms of SS18–SSX-
mediated oncogenesis are intimately related to dysregulation
of SWI/SNF chromatin remodeling.
SWI/SNF functions to reposition nucleosomes on genomic
DNA, and can also promote nucleosome disassembly and his-
tone exchange (reviewed in ref. 21 ). The canonical activity of
SWI/SNF is to create nucleosome-depleted regions at core
promoters and regulatory regions, facilitating transcription
factor access to DNA. SWI/SNF activity is broadly recruited
across the genome to effect switches in chromatin state and
has been associated with the induction of a wide range of
transcriptional programs, including cell-cycle control, stem
cell maintenance, and differentiation. Importantly, recent
exome sequencing studies have found mutations in SWI/SNF
complex members in 20% of cases across a broad spectrum of
tumor types, surveyed by Kadoch and colleagues ( 22 ), who
Figure 1. Protein interaction domains involved in synovial sarcoma translocations, where SS18 is fused to one of the highly paralogous SSX1 or SSX2 genes. Translocation breakpoints (vertical arrowheads) result in the fusion of almost all SS18 sequence to the C-terminal region of SSX protein. Protein domains: SNH, SS18 N-terminal homology; QPGY, glutamine/proline/glycine/tyrosine–enriched domain; KRAB, Kruppel-associated box domain; DD, diver-gent domain; RD, repression domain; NLS nuclear localization signal. A conserved site for ubiquitin modifi cation at lysine 13 of SS18 is shown (K13Ub), as well as a site of ubiquitin/acetyl modifi cation at lysine 124 of SSX1 (K124).
SS18
QPGY RDDDKRABSNH
SIN3A
K13Ub∗
K124∗
ATF2
BRG1, BRM
EP300
MLLT10 (AF10)
RBM14 (COAA, SIP)
SSX
SS18
418
188
TLE1
NLS
Histone
LHX4
β-catenin
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Nielsen et al.REVIEW
review the importance of this complex in tumor suppres-
sion. However, the specifi c mechanisms of tumor suppression
remain elusive, due to the diverse and tissue-specifi c roles of
the complex in transcriptional regulation.
SMARCB1 and BRG1 inactivation lead to increased prolifera-
tion ( 23 ), at least in part due to impaired transcriptional activa-
tion of the CDKN2A / B tumor suppressors ( 24 ). This result has
been related to the requirement of SWI/SNF activity for the
eviction of repressive polycomb complexes from chromatin,
and highlights the general principle of antagonism between
SWI/SNF and polycomb activities. In this regard, the domi-
nance of polycomb repression would have profound implica-
tions for the regulation of stemness and differentiation, and
may prove to be a central aspect of oncogenesis in SWI/SNF–
mutated tumors. Other mechanisms of SWI/SNF oncogenesis
have been elaborated, including mutations in ARID1A , where
it has been suggested that functional SWI/SNF is required to
execute the p53 transcriptional response ( 25 ). Although not
shown in synovial sarcoma, such an effect may explain the
lack of TP53 mutation in the majority of these lesions. SWI/
SNF dysfunction also compromises DNA double-strand break
repair, and may confer sensitivity to DNA-damaging agents
( 26 ); this may contribute to the sensitivity of synovial sarcoma
to radio- and anthracycline therapies.
SS18–SSX and Epigenetic Transcriptional Repression
Whereas SS18, through its interactions with the SWI/SNF
complex, might be expected to have a role in transcriptional
activation, its fusion partner SSX associates with the poly-
comb repressor complex, which has opposing effects. An
early observation was that SS18–SSX localizes at discrete
nuclear foci within BMI1-labeled polycomb bodies ( 27 ). More
recently chromatin immunoprecipitation sequencing (ChIP-
Seq) results from HA-FLAG–tagged SS18–SSX, expressed in
transfected C2C12 mouse myoblasts ( 28 ), correlated SS18–
SSX binding with polycomb-marked nucleosomes (trimethyl-
ated histone H3K27) at a subset of genomic H3K27me3 sites.
In studies investigating possible target genes for SS18–
SSX-mediated repression, expression profi ling ( 29 ) showed
the tumor suppressor EGR1 to be among the most consist-
ently downregulated genes in synovial sarcoma. ChIP studies
revealed the presence of SS18–SSX at a cyclic AMP response
element ( CRE ) in the EGR1 promoter ( 30 ). Furthermore,
inhibitors of histone deacetylases (HDAC)—whose antican-
cer activity had been shown previously in synovial sarcoma
xenografts ( 31 )—were found to reverse the repression of EGR1 ,
accompanied by loss of polycomb residency at this locus.
Subsequent studies detailed proteomic and biochemical
characterizations of SS18–SSX-binding partners, and identi-
fi ed Activating Transcription Factor 2 (ATF2) as the transcrip-
tion factor responsible for targeting the fusion oncoprotein
to CRE sites ( 32 ). Moreover, these studies identifi ed a robust
interaction of the transcriptional corepressor Transducin-
Like Enhancer of Split 1 (TLE1) with the SSX portion of
the fusion oncoprotein in human and mouse model syno-
vial sarcoma cells, confi rmed in surgically excised patient
tumor tissue. SS18–SSX serves as a bridge between ATF2
and TLE1, mediating repression of ATF2 targets, including
among others EGR1 , ATF3 , and CDKN2A . Both the SWI/SNF
component BRM and the polycomb component EZH2 were
observed to coelute with the SS18–SSX oncoprotein. Recip-
rocal immunoprecipitations showed copurifi cation of core
PRC2 subunits EZH2, SUZ12, and EED with TLE1, SS18–
SSX, and ATF2, indicating the presence of a stable repressive
complex nucleated by the fusion oncoprotein. ChIP and
electrophoretic mobility shift assays confi rmed the presence
of this repressive complex at conserved CRE elements in ATF2
target gene promoters. Treatment with HDAC inhibitors dis-
rupts this complex ( 32 ).
TLE family proteins are corepressors of WNT target genes
( 33 ) and effectors of HES-mediated NOTCH repression ( 34 ),
and are highly expressed in a number of embryonic progeni-
tor fi elds where these pathways are known to regulate self-
renewal and stemness. The identifi cation of the corepressor
TLE1 as an SS18–SSX-interacting protein is also signifi cant
because expression profi ling experiments have identifi ed
TLE1 as among the most consistently highly expressed genes
in primary synovial sarcoma specimens ( 29 , 35 ). Incidentally,
nuclear expression of TLE1 is readily detectable by immuno-
histochemistry on formalin-fi xed paraffi n-embedded tissues,
and its diagnostic value for synovial sarcoma has been con-
fi rmed ( 36, 37 ), leading to its adoption into clinical use.
THE CELLULAR BACKGROUND FOR SS18–SSX ONCOGENESIS
The above fi ndings contribute to knowledge about SS18–
SSX target genes and/or the cellular background in which the
oncogene operates, but do not clear up enduring mysteries
about the true cell of origin for synovial sarcoma or its line
of differentiation. Despite the name, synovial sarcoma is not
derived from synovium, nor does it differentiate into synovial-
type tissue. The term synovial sarcoma is actually a misnomer
carried over from older literature that postulated synovial dif-
ferentiation based on the propensity for this malignancy to
originate in periarticular regions, and the presence (especially
in biphasic cases) of some reminiscent histology. Synovial sar-
comas do indeed display unusual morphologic features that
are suggestive of a capacity for pluripotential differentiation.
Whereas approximately 75% of cases are “monophasic” spin-
dle cell tumors, the less common biphasic variant constitutes
a pathognomonic example of true mesenchymal–epithelial
transition, with formation of internal epithelial surfaces and
even glandular structures. This epiphenomenon is driven by
variable repression of E-cadherin by SS18–SSX interactions
with the SNAIL and SLUG transcription factors ( 38 ). The
predominant mesenchymal component in synovial sarcoma
can grow as a pure sheet of plump spindle cells reminiscent
of embryologic mesenchyme, but can alternatively display
variable degrees of multilineage mesenchymal differentiation
( 39 ), with some cases producing loosely myxoid, densely col-
lagenized, or even osteoid-type extracellular matrix.
An intriguing observation whose relevance to the cell of
origin of synovial sarcoma remains unclear came from the
discovery that a mouse model of monophasic synovial sar-
coma can be generated by conditional expression of human
SS18 – SSX2 in a MYF5 early skeletal muscle precursor (myo-
blast) population ( 11 ). These tumors arose with 100% pen-
etrance, with no other cooperating background transgenes
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required. Expression in later stage MYF6 + myoblasts caused
myopathy but no tumors, whereas cleavage-stage embryo
expression or conditional expression in earlier (PAX3 + or
PAX7 + ) myoblast populations was embryonic lethal, as was
expression of SS18 – SSX2 in early ectoderm (AP2 + ), bone/carti-
lage (SOX9 + ), endothelial (FLK1 + ; TIE2 + ), or neural (Nestin1 + )
precursor populations ( 40 ). However, a tamoxifen-induced
conditional expression model leads to development of less
aggressive synovial sarcomas in a somewhat different ana-
tomical distribution (including paraspinal and facial pri-
mary sites), suggesting that backgrounds other than MYF5 +
myoblasts may also be permissive for SS18–SSX oncogenesis.
Notably, neither in mouse models nor in human tissues do
the synovial sarcoma tumors express biomarkers typical of
muscle differentiation.
Whereas expression of SS18–SSX in most cellular back-
grounds appears to precipitate cell death, pluripotential stem
cells as well as human mesenchymal stem cells are permis-
sive—although importantly the expression profi les induced
by SS18–SSX in these two precursor populations are very
different ( 41 ). HEK293 cells can also be successfully engi-
neered to express SS18–SSX, but as mentioned above, differ-
ent oncoprotein complexes appear to be formed in transient
transfection versus stably transfected models. In this regard,
the high levels of TLE1 observed in synovial sarcoma may
be crucial, considering its possibly central role in recruiting
repressive activities to target promoters. Expression of TLE1
and its interacting transcription factors in stem/progenitor
cells may help defi ne permissive lineages for the develop-
ment of tumors in transgenic animals. These observations
highlight a major limitation of most engineered models of
synovial sarcoma—the cellular background is probably not
correct. Therefore, it is critical that experimental fi ndings
attributed to synovial sarcoma biology from experimental
systems are verifi ed in models derived from primary human
tumor tissue expressing SS18–SSX under its endogenous
promoter. These include several published cell lines grown
as monolayers, 3D spheroids ( 42 ) or xenografts ( 43 ). Results
ultimately will have to be verifi ed on patient tissue samples.
Methodologically, verifi cation of SS18 – SSX fusion transcript
expression is an important way to confi rm model or tissue
integrity in synovial sarcoma research.
ADDITIONAL MOLECULAR CHANGES FOUND IN SYNOVIAL SARCOMA TUMORS Chromosomal Alterations in Synovial Sarcoma
Synovial sarcoma differs from most common forms of
cancer by virtue of having much lower genetic complex-
ity. Almost half of primary tumors have no chromosomal
aberrations other than t(X;18), and the remainder display
only small numbers of changes (median 2–4; ref. 44 ). Nota-
bly, tumors with a balanced t(X;18) and no other genomic
changes can show a completely “fl at” genomic copy-number
profi le. Additional genomic copy-number changes, which
are more common in adults (>18 years) than in pediatric
patients, are strongly associated with metastatic spread and
poor outcomes. Not surprisingly, metastatic and recurrent
tumors display increased chromosomal complexity ( 45 ).
Secondary Mutations in Synovial Sarcoma In keeping with the observed chromosomal stability, the
most commonly mutated gene in human cancer, TP53 , is
rarely mutated in synovial sarcoma, occurring in 11 of 92
cases across three published studies ( 46–48 ); in these studies,
copy-number gains in the p53-suppressing oncogene MDM2
were somewhat more frequent. Overall, wild-type p53 appears
to be retained in most synovial sarcomas, although its func-
tion may be impaired through upstream regulatory events, as
in several well-described prosurvival interactions within the
AKT–PTEN pathway.
Otherwise, targeted sequencing approaches have high-
lighted mutations in PTEN , CTNNB1 , and APC in 8% to 14%
of cases ( 49–51 ), providing some support for oncogenic acti-
vation of the AKT–mTOR and WNT signaling pathways in
this sarcoma (see below).
As of this writing, only one whole-exome sequencing study
had been published on synovial sarcoma, on tumors from 7
patients ( 9 ). This work identifi ed an average of eight somatic
mutations per tumor exome, and no genomic losses in the
majority of cases. Solitary mutations in cancer pathway genes
were identifi ed for TP53 , SETD2 , and FBXW7 .
On the whole, these results suggest an encouraging setting
for targeted therapy of synovial sarcoma—if treated early in its
natural history, when the majority of tumors do not exhibit
genomic instability or extensive genomic rearrangements. Cell
death pathways and growth controls may be largely intact
and responsive to effective targeting of SS18–SSX. Compared
with most common cancer types, there may be fewer escape
mechanisms for emergence of therapy-resistant subclones in
synovial sarcoma.
Gene and Protein Expression in Synovial Sarcoma A major theme from gene-expression profi ling studies of
synovial sarcoma relates to high expression of mediators
involved in the patterning systems of early embryogenesis,
including WNT ( LEF1 , AXIN2 , WIF1 , WNT5A , and FZD10 ),
NOTCH ( HES1 , JAG1 , JAG2 , and NRARP ), Hedgehog ( PTCH1 ,
GLI1 , and GLI2 ), FGF ( FGFR2 , FGFR3 , FGF18 , and FGF9 ),
and BMP pathways ( BMP7 , BMP5 , BMPR2 , and SOSTDC1 ).
These results and expression of other markers of embryonic
primordia ( SALL2 , TLE1 , SIX1 , SIX4 , and DLX2 ) support the
idea that synovial sarcoma cells have a stem-like or early pro-
genitor phenotype. Of note, primary synovial sarcomas show
a remarkable correspondence with the expression profi les of
the conditional MYF5–CRE mouse model ( 11 ) and SS18 – SSX -
transduced embryonic stem cells ( 41 ).
Synovial sarcomas commonly express relatively high levels
of mRNA for cancer–testis antigens, a group of potentially
immunogenic proteins expressed in many tumor types, but
not in normal adult tissues outside the germline: PRAME ,
CTAG1A (encoding NY-ESO-1), and MAGEE1 are promi-
nent examples. The possible relevance of this aberrant anti-
gen expression in terms of response in recently developed
immuno therapy approaches remains to be determined.
High expression of neural ( NPTX2 , NEFH , and NTNG2 )
and chondrocyte ( COL2A1 , COL9A3 , SOX9 , and TRPS1 ) line-
age markers has been interpreted as consistent with differen-
tiation from neural crest progenitors. High mRNA expression
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Nielsen et al.REVIEW
of SOX2 , an important determinant of neural progenitors and
embryonic stem cells, is common in synovial sarcoma and has
been shown to be critical for growth of some cell lines in vitro
( 15 , 39 ). However, its expression is absent in other cell lines
and is not a universal feature of primary tumor specimens.
Other notable features of the synovial sarcoma profi le
include differential high expression of BCL2 , as well as of the
receptor tyrosine kinases (RTK) PDGFRA , EGFR , and ERBB2 .
The latter group may be important for the stimulation of
PI3K–AKT signaling, which has been reported as critical to
synovial sarcoma viability in several studies ( 52, 53 ), and is
discussed further below.
Many of the above fi ndings have been confi rmed at the pro-
tein level in patient specimens, including FZD10 ( 54 ), HES1
( 55 ), NY-ESO-1 ( 56 ), BMPR2 ( 57 ), SALL2 and EGFR ( 58 ),
BCL2 ( 59 ), SOX9 ( 60 ), FGFs and their receptors ( 61 ), PDGFRA
( 52 ), and WNT pathway mediators (discussed further in the
next section).
TARGETABLE ONCOGENIC PATHWAYS ACTIVE IN SYNOVIAL SARCOMA WNT–b-Catenin Signaling Pathway
There has been longstanding evidence for WNT activa-
tion in a subset of synovial sarcomas. Sanger sequencing
studies found canonical activating mutations in CTNNB1 ,
at frequencies of 4% ( N = 24; ref. 62 ), 8% ( N = 49; ref. 63 ),
and 12% ( N = 16; ref. 50 ), and APC mutations in 8% ( N =
49) of cases ( 51 ). At the protein level, WNT pathway activa-
tion, as evidenced by nuclear accumulation of β-catenin, has
been studied using immunohistochemistry. By this method,
nuclear accumulation of β-catenin is detected in 30% to 60%
of synovial sarcomas ( 64, 65 ), primarily in monophasic cases
or in the spindle cell component of biphasic cases. The SYO-1
synovial sarcoma cell line harbors a codon 34 mutation in
CTNNB1 (G34L) with concomitant protein accumulation
and shows reduced proliferation and impairment in stand-
ard invasion and migration assays when transfected with an
inhibitory dominant-negative LEF1 construct (T. Saito and
colleagues; unpublished data).
Recently, two independent studies have provided impor-
tant functional evidence for a critical role of this signaling
pathway in synovial sarcoma. Barham and colleagues ( 66 )
showed that genetic loss of β-catenin blocks tumor formation
in the MYF5–CRE SS18–SSX2 transgenic model described
above. To confi rm this observation in the human setting,
they showed that pharmacologic activation of CSNK1A by
pyrvinium, known to inhibit β-catenin signaling, or RNAi
knockdown of LRP6 could both impair growth of human
synovial sarcoma cell lines. These investigators also showed
that SS18–SSX can induce nuclear β-catenin accumulation,
apparently by inducing autocrine signaling through its aber-
rant transcriptional effects. These data may explain the fact
that the proportion of human synovial sarcoma tumors with
nuclear β-catenin accumulation is several fold higher than
the rate of CTNNB1 or APC mutations.
In a separate recent study, Trautmann and colleagues ( 67 )
found that introduction of SS18–SSX into HEK293 cells
induced activation of WNT–β-catenin signaling. Conversely,
small-molecule TCF–β-catenin complex inhibitors reduced cell
viability in vitro in fi ve human synovial sarcoma cell lines and
reduced in vivo growth of xenografted SYO-1 synovial sarcoma
cells.
Together, these studies nominate the WNT–β-catenin sig-
naling pathway as an important new candidate therapeutic
target in synovial sarcoma, with putative mechanisms as
outlined in Fig. 2 . As new agents effi ciently targeting this
pathway are in clinical development, these studies provide
a critical preclinical rationale for their evaluation in clini-
cal trials ( 68, 69 ). Beyond the direct targeting of WNT–β-
catenin signaling pathway components by small molecules,
targeting of key interacting proteins also offers therapeutic
opportunities. For instance, β-catenin forms a complex with
the transcriptional modulator YAP1 and the YES1 tyrosine
kinase, which may explain why dasatinib, which blocks the
latter, also inhibits WNT–β-catenin–dependent prolifera-
tion ( 69 ). Interestingly, a recent study found that dasatinib
caused apoptosis and inhibition of cellular proliferation in
synovial sarcoma cells; some data support that this effect
is mediated by inhibition of activated SRC ( 70 ), but it is
tempting to speculate that the potency of the drug may also
have been due to concurrent effects on WNT–β-catenin–
dependent targets.
In light of the recent fi nding that SS18–SSX may, under
certain circumstances, displace SMARCB1 from SWI/SNF
chromatin remodeling complexes ( 17 ), it is also notable that
loss of SMARCB1 results in activation of WNT–β-catenin sig-
naling in mouse and cell culture models, refl ecting a role for
the SWI/SNF complex in regulating this pathway ( 71 ).
AKT–MTOR Signaling Pathway Various lines of evidence also support an important role
for the AKT–mTOR pathway in synovial sarcoma, including
genetic, protein level, preclinical, and clinical trial data. At the
genetic level, PTEN mutations are found in only a minority of
cases ( 49 , 62 , 72 ) and canonical PIK3CA mutations are even
more uncommon ( 72 ). Nonetheless, several groups have dem-
onstrated frequent activation of AKT in synovial sarcoma,
and its dependency on upstream RTKs ( 53 , 73 , 74 ). As noted
above, apoptosis induction in synovial sarcoma cell lines by
HDAC inhibitors is at least partially dependent on derepres-
sion of EGR1 and subsequent induction of PTEN ( 30 ), a phe-
nomenon that may help to identify strategic combinations
involving these promising therapeutic agents.
Notably, fundamental interactions of PI3K–AKT–mTOR and
RAS–MEK–ERK pathways have been identifi ed downstream of
RTK signaling, and multiple levels of feedback regulation have
been identifi ed within and between these pathways, as summa-
rized in Fig. 3 . These interactions underlie intrinsic resistance
to PI3K–AKT–mTORC1-targeted monotherapies in synovial
sarcoma, for example, involving feedback activation of AKT
following mTOR inhibition, which can be mediated by either
IFG1R or PDGFRA ( 43 , 52 ). These data support the combina-
tion of mTOR inhibitors with inhibitors of particular RTKs
that potentiate feedback AKT activation in a given tumor. Strat-
egies that may intercept these signals at critical downstream
nodes are also under investigation, including the combination
of PI3K and MEK inhibitors, and the use of pan-mTOR kinase
inhibitors targeting both mTORC1 and mTORC2 (which are
not associated with reactivation of AKT; ref. 75 ).
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Antiapoptotic Pathways Histologically, synovial sarcomas typically display few
mitotic fi gures, while also displaying few apoptotic bodies.
The tumor’s propensity in many cases for slow growth, late
recurrences, and chemotherapy resistance is consistent with
an antiapoptotic phenotype. A striking feature of synovial
sarcoma is its consistently very high expression of BCL2 ( 59 ,
76 , 77 ), but no evidence has been found that the BCL2 gene
is a direct target for transcriptional upregulation by SS18–
SSX; therefore, its high level of expression may be a second-
ary oncogenic effect, or may refl ect a prerequisite cellular
background to be permissive for SS18–SSX. In contrast, the
BCL2 family members BCL2A1 and MCL1 are direct targets
for SS18–SSX-mediated repression. Resistance to new BH3
mimetic BCL2 inhibitors in lymphomas is typically induced
by activation of MCL1, but this escape mechanism is not
available to synovial sarcomas, which appear to be highly
sensitive to such drugs in human cells and an SS18 – SSX2
mouse tumor model ( 78 ). These fi ndings suggest that BCL2
inhibitors may be worth evaluating in synovial sarcoma,
perhaps in combination with apoptosis-inducing cytotoxic
chemotherapy, but as yet no such clinical trials have been
opened.
CLINICAL TRIALS IN SYNOVIAL SARCOMA Table 1 summarizes several trials in which synovial sarcoma
may be included as an eligible diagnosis. Given its low inci-
dence and a patient population split between pediatric and
adult institutions, synovial sarcoma disease-specifi c trials have
to date been largely precluded by logistical challenges. Instead,
patients with this well-defi ned and unique sarcoma have gen-
erally been lumped with patients with other soft-tissue sar-
comas, as in current trials of multitargeted TKIs (pazopanib:
NCT02180867; regorafenib: NCT01900743). More closely
tied to some of the biologic dependencies of synovial sarcoma
Figure 2. Putative mechanisms for autocrine/paracrine activation of WNT signaling in synovial sarcoma. WNT signals through FZD/LRP6, inhibiting the APC–AXIN–GSK3B–CSNK1 destruction complex, leading to release and nuclear transport of β-catenin (CTNNB1). SS18–SSX integrates within SWI/SNF complexes, with potential interactions with developmental pathways, including NOTCH–HES, BMP–SMAD, Hedghog–GLI, MAPK–ETS, and LEF1–TLE1. Extensive cross-regulation between developmental pathways may lead to transcriptional activation of WNT ligands and/or derepression of WNT target genes. The sites of action of WNT inhibitors PRI-724 and LGK974 are indicated.
WNT
WNT
FZD LRP6
Cytoplasm
Destruction complex
ProteasomeCTNNB1
SWI/SNF
GLISMADHESETS
Nucleus
POLII
CBPLEF1
CTNNB1
?
LEF1TLE1
HDACTLE1
SS18/SSX
BRG1
PRI-724
Wnt targets
POLII
CBP?Wnt ligands
JAG2, CCND1, LEF1,
AXIN2, WNT11
AX
IN
GSK3B
CSNK1
CTNNB1
APC
+Ub**
Acyltransferase
PORCNLGK974
DVL
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Nielsen et al.REVIEW
Figure 3. Drug targets downstream of RTKs involved in synovial sarcoma. Extensive cross-talk and feedback regulation are observed in prosurvival signaling through MAPK–ERK and AKT–mTOR pathways. Intrinsic drug resistance to monotherapies can be mediated by activation of prosurvival signaling in either pathway, due to removal of inhibitory feedback (red lines). Drug targets discussed in the text are shown in green. BH3 represents pro apoptotic BH3 domain–only proteins, and their activation by stress-activated protein kinases is shown (SAPK: JNK, p38). Dashed lines represent nuclear export and translation of mRNA to protein.
RHEB
BH3 (BIM, PUMA, NOXA)
DUSP1, DUSP10
PTENEGR1, MCL1
AP1
EGR1
FOXO3
TLE1
ATF2
SS18/SSX
PRC2HDAC
ELK1
GSK3B
Plasma membrane
Mitochondrion
Cytoplasm
Nucleus
BCL2
BAX
BAD
DUSPSAPK
BH3
AKT
FOXO3TSC1/2
mTOR
RICTOR
mTOR
RAPTOR
GRB10
S6K
FBXW8
PTEN
PDK1
PI3K
PIP2 PIP3
IRS1
ERK
MEK
RAF
RAS
FGFR/PDGFR/IGF1R
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Advances in Synovial Sarcoma REVIEW
described above are efforts to test histone deacetylase inhibi-
tors (including vorinostat: NCT01879085, NCT01294670)
and IGF1R/mTOR inhibitor combinations (cixutumumab/
temsirolimus: NCT01614795). Most of the above studies will
incorporate preplanned disease-specifi c subgroup analyses,
but most likely will remain severely underpowered to identify
signifi cant activity specifi cally against synovial sarcoma.
Inhibitors of the Hedgehog and NOTCH pathways are in
earlier stages of development, but are already being tested in
phase II studies that include synovial sarcoma among the eli-
gible diagnoses (vismodegib + RO4929097: NCT01154452).
The fi rst phase I trials of WNT inhibition in advanced solid
tumors may constitute important referrals for synovial sar-
coma. These include the agent PRI-724 that blocks the inter-
action of β-catenin with CBP (NCT01302405). Another new
trial (NCT01351103) is of LGK974, an inhibitor of PORCN,
an acyltransferase required for secretion of active WNT lig-
and; referral to this trial is contingent on demonstration of
tumors with WNT ligand dependency, and this may require
further preclinical studies for synovial sarcoma.
Expression of the WNT receptor Frizzled class receptor 10
(FZD10) is consistently high in synovial sarcoma, and there
is an open synovial sarcoma–specifi c trial using a Ytrium-90–
labeled antibody to this receptor (NCT01469975). FZD10 is
reported to couple to noncanonical (β-catenin–independent)
WNT signaling in synovial sarcoma cells, and the unlabeled
antibody has only weak inhibitory activity against growth
of these cells. However, FZD10 is not expressed on normal
cells of vital organs, and as such it is excellent for targeting
the radioisotope specifi cally to synovial sarcoma tumor cells.
Antibody-based approaches may additionally work by
inducing antitumor immune responses; other immuno-
therapy strategies include blockade of immune checkpoints
and eliciting responses to neoantigens. Recent successes
involving inhibition of immune checkpoints have led to a
general resurgence of interest in immunotherapy for solid
tumors. Potential immunogenic CT antigens expressed in
synovial sarcoma but not normal tissues have been identifi ed,
including NY-ESO-1, an antigen that is the basis for several
open trials, using strategies such as adoptive T-cell transfer
(NCT01477021) or dendritic cell activation (NCT02122861).
Direct targeting of SS18–SSX oncoprotein has been
attempted using peptide vaccination with an MHC class
1–binding epitope of the oncoprotein, in a small trial of 21
patients, of whom 8 were unable to complete the 12-week vac-
cination schedule due to disease progression ( 79 ). Four arms
of the trial were defi ned, depending on the use of agretope-
modifi ed peptide with increased affi nity for HLA-A24, and on
the addition of Freund’s incomplete adjuvant with IFNα. No
robust immune responses were detected as measured using
delayed type hypersensitivity and tetramer assays, designed
to show the presence of antigen-specifi c CD8 + T cells. These
results are in line with the limited clinical effi cacy of MHC-I
peptide vaccines, but may also relate to the generally observed
lack of infl ammatory infi ltrates in synovial sarcoma. The
basis of immune evasion in synovial sarcoma is unknown, but
may be due to limited neoantigen production in these hypo-
mutated tumors, low expression of class I MHC, or to other
immune suppression mechanisms active in mesenchymal
cells with stem/progenitor phenotypes.
Chimeric antigen receptor T cells represent another promising
approach, in which T cells are engineered to express a chimeric
T-cell receptor, whose signaling components are fused with an
antibody fragment specifi c to a surface antigen on tumor cells.
Activation of costimulatory signals is also engineered, so that
the chimeric antigen receptor T cells are able to bypass immune
checkpoints, recognizing and killing tumor cells independent
of MHC antigen presentation. Given the unique and markedly
elevated expression of FZD10 in synovial sarcoma, this would
seem to represent an attractive target for this technology.
FUTURE PERSPECTIVES Despite genomic and clinical progression, the SS18–SSX
fusion gene is consistently retained in synovial sarcoma, and
synovial sarcoma cells depend on continued SS18–SSX expres-
sion throughout the course of disease. This provides a basis
for monitoring disease recurrence, through PCR detection
Table 1. Summary data for clinical trials referenced in the text
NCI trial Agent 1 Agent 2 Target accrual Start/end Phase
NCT02180867 Pazopanib Radiation/chemoradiation 340 2014–2018 II/III
NCT01900743 Regorafenib 192 2013–2016 II
NCT01879085 Vorinostat Gemcitabine + docetaxel 62 2013–2020 IB/II
NCT01294670 Vorinostat Etoposide 50 2011–2015 I/II
NCT01614795 Temsirolimus Cixutumumab 45 2012–2013 II
NCT01154452 RO4929097 Vismodegib 120 2010–2014 IB/II
NCT01302405 PRI-724 54 2011–2014 IA/IB
NCT01351103 LGK974 80 2012–2015 I
NCT01469975 OTSA101-DTPA-90Y 18 2011–2014 I
NCT01477021 Autologous T cells Cyclophosphamide 7 2012–2014 I
NCT02122861 ID-LV305 36 2014–2016 I
NCT01058707 MLN0128 190 2010–2014 I
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Nielsen et al.REVIEW
of the fusion gene in circulating tumor cells or in free tumor
DNA in plasma. As more effective systemic treatments evolve,
the clinical utility of such tests will become more signifi cant.
Agents that directly target the fusion oncoprotein and its
interactions remain the Holy Grail for the fi eld, and several
newer proximity-based assays could, in principle, be adapted
for high-throughput screening of small-molecule inhibitors.
Given the broad scope and ubiquity of such fundamental
interactions in normal tissues—for example, between SS18
domains and BRG1—in the short term, it may be more fea-
sible to target the critical enzymatic cofactors of SS18–SSX
(such as histone-modifying transcriptional effectors) or the
critical oncogenic pathways it induces. In this regard, EZH2
inhibitors are under investigation in synovial sarcoma models
and early-phase clinical trials. Screening experiments identify-
ing additional epigenetic dependencies are expected to yield
further mechanistic insights, which may guide additional
therapeutic strategies. Finally, given the challenges involved
in opening, accruing, and executing well-powered synovial
sarcoma–specifi c trials, it is possible that drug-repurposing
strategies will provide another set of opportunities for thera-
peutic advances. In cases where there is a good match between
drug mechanism and oncogenic pathway, drugs developed for
more common cancers may in fact work even better in a more
genetically homogeneous malignancy like synovial sarcoma.
Disclosure of Potential Confl icts of Interest No potential confl icts of interest were disclosed.
Acknowledgments The authors thank Drs. B Brodin and T. Ito for insightful discus-
sions and for their review of this article. The authors acknowledge the
contributions of the many sarcoma researchers whose work they are
unable to reference due to space limitations.
Grant Support This work was supported by Terry Fox Research Institute grant no.
1021 (to T.O. Nielsen), Canadian Cancer Society Research Institute
grant no. 701582 (to T.O. Nielsen), the Liddy Shriver Sarcoma Initia-
tive (to T.O. Nielsen and M. Ladanyi), and National Cancer Institute
SPORE grant P50 CA140146 (to M. Ladanyi).
Received October 23, 2014; revised December 23, 2014; accepted
December 29, 2014; published OnlineFirst January 22, 2015.
REFERENCES 1. Herzog CE . Overview of sarcomas in the adolescent and young adult
population . J Pediatr Hematol Oncol 2005 ; 27 : 215 – 8 .
2. Ladanyi M , Antonescu CR , Leung DH , Woodruff JM , Kawai A , Healey
JH , et al. Impact of SYT-SSX fusion type on the clinical behavior of
synovial sarcoma: a multi-institutional retrospective study of 243
patients . Cancer Res 2002 ; 62 : 135 – 40 .
3. Sultan I , Rodriguez-Galindo C , Saab R , Yasir S , Casanova M , Ferrari
A . Comparing children and adults with synovial sarcoma in the Sur-
veillance, Epidemiology, and End Results program, 1983 to 2005: an
analysis of 1268 patients . Cancer 2009 ; 115 : 3537 – 47 .
4. Spurrell EL , Fisher C , Thomas JM , Judson IR . Prognostic factors in
advanced synovial sarcoma: an analysis of 104 patients treated at the
Royal Marsden Hospital . Ann Oncol 2005 ; 16 : 437 – 44 .
5. Al-Hussaini H , Hogg D , Blackstein ME , O’Sullivan B , Catton CN ,
Chung PW , et al. Clinical features, treatment, and outcome in 102
adult and pediatric patients with localized high-grade synovial sar-
coma . Sarcoma 2011 ; 2011 : 231789 .
6. Clark J , Rocques PJ , Crew AJ , Gill S , Shipley J , Chan AM , et al.
Identifi cation of novel genes, SYT and SSX, involved in the t(X;18)
(p11.2;q11.2) translocation found in human synovial sarcoma . Nat
Genet 1994 ; 7 : 502 – 8 .
7. Skytting B , Nilsson G , Brodin B , Xie Y , Lundeberg J , Uhlen M , et al. A
novel fusion gene, SYT-SSX4, in synovial sarcoma . J Natl Cancer Inst
1999 ; 91 : 974 – 5 .
8. Panagopoulos I , Mertens F , Isaksson M , Limon J , Gustafson P , Skyt-
ting B , et al. Clinical impact of molecular and cytogenetic fi ndings in
synovial sarcoma . Genes Chromosomes Cancer 2001 ; 31 : 362 – 72 .
9. Joseph CG , Hwang H , Jiao Y , Wood LD , Kinde I , Wu J , et al. Exomic
analysis of myxoid liposarcomas, synovial sarcomas, and osteosarco-
mas . Genes Chromosomes Cancer 2014 ; 53 : 15 – 24 .
10. Carmody Soni EE , Schlottman S , Erkizan HV , Uren A , Toretsky JA .
Loss of SS18–SSX1 inhibits viability and induces apoptosis in syno-
vial sarcoma . Clin Orthop Relat Res 2014 ; 472 : 874 – 82 .
11. Haldar M , Hancock JD , Coffi n CM , Lessnick SL , Capecchi MR . A con-
ditional mouse model of synovial sarcoma: insights into a myogenic
origin . Cancer Cell 2007 ; 11 : 375 – 88 .
12. Brett D , Whitehouse S , Antonson P , Shipley J , Cooper C , Goodwin G .
The SYT protein involved in the t(X;18) synovial sarcoma transloca-
tion is a transcriptional activator localised in nuclear bodies . Hum
Mol Genet 1997 ; 6 : 1559 – 64 .
13. Perani M , Antonson P , Hamoudi R , Ingram CJ , Cooper CS , Garrett
MD , et al. The proto-oncoprotein SYT interacts with SYT-interacting
protein/co-activator activator (SIP/CoAA), a human nuclear receptor
co-activator with similarity to EWS and TLS/FUS family of proteins .
J Biol Chem 2005 ; 280 : 42863 – 76 .
14. Thaete C , Brett D , Monaghan P , Whitehouse S , Rennie G , Rayner E ,
et al. Functional domains of the SYT and SYT-SSX synovial sarcoma
translocation proteins and co-localization with the SNF protein BRM
in the nucleus . Hum Mol Genet 1999 ; 8 : 585 – 91 .
15. Kato H , Tjernberg A , Zhang W , Krutchinsky AN , An W , Takeuchi
T , et al. SYT associates with human SNF/SWI complexes and the
C-terminal region of its fusion partner SSX1 targets histones . J Biol
Chem 2002 ; 277 : 5498 – 505 .
16. Middeljans E , Wan X , Jansen PW , Sharma V , Stunnenberg HG , Logie
C . SS18 together with animal-specifi c factors defi nes human BAF-
type SWI/SNF complexes . PLoS ONE 2012 ; 7 : e33834 .
17. Kadoch C , Crabtree GR . Reversible disruption of mSWI/SNF (BAF)
complexes by the SS18–SSX oncogenic fusion in synovial sarcoma .
Cell 2013 ; 153 : 71 – 85 .
18. Jackson EM , Sievert AJ , Gai X , Hakonarson H , Judkins AR , Tooke L , et al.
Genomic analysis using high-density single nucleotide polymorphism-
based oligonucleotide arrays and multiplex ligation-dependent probe
amplifi cation provides a comprehensive analysis of INI1/SMARCB1 in
malignant rhabdoid tumors . Clin Cancer Res 2009 ; 15 : 1923 – 30 .
19. Le Loarer F , Zhang L , Fletcher CD , Ribeiro A , Singer S , Italiano A ,
et al. Consistent SMARCB1 homozygous deletions in epithelioid
sarcoma and in a subset of myoepithelial carcinomas can be reliably
detected by FISH in archival material . Genes Chromosomes Cancer
2014 ; 53 : 475 – 86 .
20. Wang X , Sansam CG , Thom CS , Metzger D , Evans JA , Nguyen PT ,
et al. Oncogenesis caused by loss of the SNF5 tumor suppressor is
dependent on activity of BRG1, the ATPase of the SWI/SNF chroma-
tin remodeling complex . Cancer Res 2009 ; 69 : 8094 – 101 .
21. Mueller-Planitz F , Klinker H , Becker PB . Nucleosome sliding mecha-
nisms: new twists in a looped history . Nat Struct Mol Biol 2013 ; 20 :
1026 – 32 .
22. Kadoch C , Hargreaves DC , Hodges C , Elias L , Ho L , Ranish J , et al.
Proteomic and bioinformatic analysis of mammalian SWI/SNF com-
plexes identifi es extensive roles in human malignancy . Nat Genet
2013 ; 45 : 592 – 601 .
23. Tolstorukov MY , Sansam CG , Lu P , Koellhoffer EC , Helming KC ,
Alver BH , et al. Swi/Snf chromatin remodeling/tumor suppressor
complex establishes nucleosome occupancy at target promoters . Proc
Natl Acad Sci U S A 2013 ; 110 : 10165 – 70 .
on June 15, 2019. © 2015 American Association for Cancer Research. cancerdiscovery.aacrjournals.org Downloaded from
Published OnlineFirst January 22, 2015; DOI: 10.1158/2159-8290.CD-14-1246
FEBRUARY 2015�CANCER DISCOVERY | 133
Advances in Synovial Sarcoma REVIEW
24. Kia SK , Gorski MM , Giannakopoulos S , Verrijzer CP . SWI/SNF medi-
ates polycomb eviction and epigenetic reprogramming of the INK4b-
ARF-INK4a locus . Mol Cell Biol 2008 ; 28 : 3457 – 64 .
25. Guan B , Wang TL , Shih Ie M . ARID1A, a factor that promotes forma-
tion of SWI/SNF-mediated chromatin remodeling, is a tumor sup-
pressor in gynecologic cancers . Cancer Res 2011 ; 71 : 6718 – 27 .
26. Watanabe R , Ui A , Kanno S , Ogiwara H , Nagase T , Kohno T , et al.
SWI/SNF factors required for cellular resistance to DNA damage
include ARID1A and ARID1B and show interdependent protein sta-
bility . Cancer Res 2014 ; 74 : 2465 – 75 .
27. Soulez M , Saurin AJ , Freemont PS , Knight JC . SSX and the synovial-
sarcoma-specifi c chimaeric protein SYT-SSX co-localize with the
human Polycomb group complex . Oncogene 1999 ; 18 : 2739 – 46 .
28. Garcia CB , Shaffer CM , Eid JE . Genome-wide recruitment to Polycomb-
modifi ed chromatin and activity regulation of the synovial sarcoma
oncogene SYT-SSX2 . BMC Genomics 2012 ; 13 : 189 .
29. Baird K , Davis S , Antonescu CR , Harper UL , Walker RL , Chen Y , et al.
Gene expression profi ling of human sarcomas: insights into sarcoma
biology . Cancer Res 2005 ; 65 : 9226 – 35 .
30. Lubieniecka JM , de Bruijn DR , Su L , van Dijk AH , Subramanian S ,
van de Rijn M , et al. Histone deacetylase inhibitors reverse SS18–SSX-
mediated polycomb silencing of the tumor suppressor early growth
response 1 in synovial sarcoma . Cancer Res 2008 ; 68 : 4303 – 10 .
31. Ito T , Ouchida M , Morimoto Y , Yoshida A , Jitsumori Y , Ozaki T ,
et al. Signifi cant growth suppression of synovial sarcomas by the
histone deacetylase inhibitor FK228 in vitro and in vivo . Cancer Lett
2005 ; 224 : 311 – 9 .
32. Su L , Sampaio AV , Jones KB , Pacheco M , Goytain A , Lin S , et al. Decon-
struction of the SS18–SSX fusion oncoprotein complex: insights into
disease etiology and therapeutics . Cancer Cell 2012 ; 21 : 333 – 47 .
33. Levanon D , Goldstein RE , Bernstein Y , Tang H , Goldenberg D , Stifani
S , et al. Transcriptional repression by AML1 and LEF-1 is mediated
by the TLE/Groucho corepressors . Proc Natl Acad Sci U S A 1998 ; 95 :
11590 – 5 .
34. Grbavec D , Stifani S . Molecular interaction between TLE1 and the
carboxyl-terminal domain of HES-1 containing the WRPW motif .
Biochem Biophys Res Commun 1996 ; 223 : 701 – 5 .
35. Nakayama R , Mitani S , Nakagawa T , Hasegawa T , Kawai A , Morioka
H , et al. Gene expression profi ling of synovial sarcoma: distinct
signature of poorly differentiated type . Am J Surg Pathol 2010 ; 34 :
1599 – 607 .
36. Valente AL , Tull J , Zhang S . Specifi city of TLE1 expression in unclassi-
fi ed high-grade sarcomas for the diagnosis of synovial sarcoma . Appl
Immunohistochem Mol Morphol 2013 ; 21 : 408 – 13 .
37. Jagdis A , Rubin BP , Tubbs RR , Pacheco M , Nielsen TO . Prospective
evaluation of TLE1 as a diagnostic immunohistochemical marker in
synovial sarcoma . Am J Surg Pathol 2009 ; 33 : 1743 – 51 .
38. Saito T , Nagai M , Ladanyi M . SYT-SSX1 and SYT-SSX2 interfere with
repression of E-cadherin by snail and slug: a potential mechanism
for aberrant mesenchymal to epithelial transition in human synovial
sarcoma . Cancer Res 2006 ; 66 : 6919 – 27 .
39. Naka N , Takenaka S , Araki N , Miwa T , Hashimoto N , Yoshioka K ,
et al. Synovial sarcoma is a stem cell malignancy . Stem Cells 2010 ; 28 :
1119 – 31 .
40. Haldar M , Hedberg ML , Hockin MF , Capecchi MR . A CreER-based
random induction strategy for modeling translocation-associated
sarcomas in mice . Cancer Res 2009 ; 69 : 3657 – 64 .
41. Hayakawa K , Ikeya M , Fukuta M , Woltjen K , Tamaki S , Takahara N ,
et al. Identifi cation of target genes of synovial sarcoma-associated
fusion oncoprotein using human pluripotent stem cells . Biochem
Biophys Res Commun 2013 ; 432 : 713 – 9 .
42. Wakamatsu T , Naka N , Sasagawa S , Tanaka T , Takenaka S , Araki
N , et al. Defl ection of vascular endothelial growth factor action by
SS18–SSX and composite vascular endothelial growth factor- and
chemokine (C-X-C motif) receptor 4-targeted therapy in synovial
sarcoma . Cancer Sci 2014 ; 105 : 1124 – 34 .
43. Yasui H , Naka N , Imura Y , Outani H , Kaneko K , Hamada K , et al.
Tailored therapeutic strategies for synovial sarcoma: receptor tyrosine
kinase pathway analyses predict sensitivity to the mTOR inhibitor
RAD001 . Cancer Lett 2014 ; 347 : 114 – 22 .
44. Lagarde P , Przybyl J , Brulard C , Perot G , Pierron G , Delattre O , et al.
Chromosome instability accounts for reverse metastatic outcomes of
pediatric and adult synovial sarcomas . J Clin Oncol 2013 ; 31 : 608 – 15 .
45. Przybyl J , Sciot R , Wozniak A , Schoffski P , Vanspauwen V , Samson
I , et al. Metastatic potential is determined early in synovial sarcoma
development and refl ected by tumor molecular features . Int J Bio-
chem Cell Biol 2014 ; 53 : 505 – 13 .
46. Schneider-Stock R , Onnasch D , Haeckel C , Mellin W , Franke DS ,
Roessner A . Prognostic signifi cance of p53 gene mutations and p53
protein expression in synovial sarcomas . Virchows Arch 1999 ; 435 :
407 – 12 .
47. Oda Y , Sakamoto A , Satio T , Kawauchi S , Iwamoto Y , Tsuneyoshi
M . Molecular abnormalities of p53, MDM2, and H-ras in synovial
sarcoma . Mod Pathol 2000 ; 13 : 994 – 1004 .
48. Ito M , Barys L , O’Reilly T , Young S , Gorbatcheva B , Monahan J ,
et al. Comprehensive mapping of p53 pathway alterations reveals an
apparent role for both SNP309 and MDM2 amplifi cation in sarcom-
agenesis . Clin Cancer Res 2011 ; 17 : 416 – 26 .
49. Saito T , Oda Y , Kawaguchi K , Takahira T , Yamamoto H , Tanaka K ,
et al. PTEN and other tumor suppressor gene mutations as secondary
genetic alterations in synovial sarcoma . Oncol Rep 2004 ; 11 : 1011 – 5 .
50. Subramaniam MM , Calabuig-Farinas S , Pellin A , Llombart-Bosch A .
Mutational analysis of E-cadherin, beta-catenin and APC genes in
synovial sarcomas . Histopathology 2010 ; 57 : 482 – 6 .
51. Saito T , Oda Y , Sakamoto A , Kawaguchi K , Tanaka K , Matsuda S ,
et al. APC mutations in synovial sarcoma . J Pathol 2002 ; 196 : 445 – 9 .
52. Ho AL , Vasudeva SD , Lae M , Saito T , Barbashina V , Antonescu CR ,
et al. PDGF receptor alpha is an alternative mediator of rapamycin-
induced Akt activation: implications for combination targeted ther-
apy of synovial sarcoma . Cancer Res 2012 ; 72 : 4515 – 25 .
53. Friedrichs N , Trautmann M , Endl E , Sievers E , Kindler D , Wurst P ,
et al. Phosphatidylinositol-3′-kinase/AKT signaling is essential in
synovial sarcoma . Int J Cancer 2011 ; 129 : 1564 – 75 .
54. Nagayama S , Fukukawa C , Katagiri T , Okamoto T , Aoyama T , Oyaizu
N , et al. Therapeutic potential of antibodies against FZD 10, a cell-
surface protein, for synovial sarcomas . Oncogene 2005 ; 24 : 6201 – 12 .
55. Ishibe T , Nakayama T , Aoyama T , Nakamura T , Toguchida J . Neuro-
nal differentiation of synovial sarcoma and its therapeutic applica-
tion . Clin Orthop Relat Res 2008 ; 466 : 2147 – 55 .
56. Jungbluth AA , Antonescu CR , Busam KJ , Iversen K , Kolb D , Coplan
K , et al. Monophasic and biphasic synovial sarcomas abundantly
express cancer/testis antigen NY-ESO-1 but not MAGE-A1 or CT7 .
Int J Cancer 2001 ; 94 : 252 – 6 .
57. Guo W , Gorlick R , Ladanyi M , Meyers PA , Huvos AG , Bertino JR ,
et al. Expression of bone morphogenetic proteins and receptors in
sarcomas . Clin Orthop Relat Res 1999 ; 365 : 175 – 83 .
58. Nielsen TO , Hsu FD , O’Connell JX , Gilks CB , Sorensen PH , Linn S ,
et al. Tissue microarray validation of epidermal growth factor recep-
tor and SALL2 in synovial sarcoma with comparison to tumors of
similar histology . Am J Pathol 2003 ; 163 : 1449 – 56 .
59. Pelmus M , Guillou L , Hostein I , Sierankowski G , Lussan C , Coindre
JM . Monophasic fi brous and poorly differentiated synovial sarcoma:
immunohistochemical reassessment of 60 t(X;18)(SYT-SSX)-positive
cases . Am J Surg Pathol 2002 ; 26 : 1434 – 40 .
60. Cajaiba MM , Jianhua L , Goodman MA , Fuhrer KA , Rao UN . Sox9
expression is not limited to chondroid neoplasms: variable occur-
rence in other soft tissue and bone tumors with frequent expression
by synovial sarcomas . Int J Surg Pathol 2010 ; 18 : 319 – 23 .
61. Ishibe T , Nakayama T , Okamoto T , Aoyama T , Nishijo K , Shibata KR ,
et al. Disruption of fi broblast growth factor signal pathway inhibits
the growth of synovial sarcomas: potential application of signal
inhibitors to molecular target therapy . Clin Cancer Res 2005 ; 11 :
2702 – 12 .
62. Barretina J , Taylor BS , Banerji S , Ramos AH , Lagos-Quintana M ,
Decarolis PL , et al. Subtype-specifi c genomic alterations defi ne new
targets for soft-tissue sarcoma therapy . Nat Genet 2010 ; 42 : 715 – 21 .
on June 15, 2019. © 2015 American Association for Cancer Research. cancerdiscovery.aacrjournals.org Downloaded from
Published OnlineFirst January 22, 2015; DOI: 10.1158/2159-8290.CD-14-1246
134 | CANCER DISCOVERY�FEBRUARY 2015 www.aacrjournals.org
Nielsen et al.REVIEW
63. Saito T , Oda Y , Sakamoto A , Tamiya S , Kinukawa N , Hayashi K , et al.
Prognostic value of the preserved expression of the E-cadherin and
catenin families of adhesion molecules and of beta-catenin mutations
in synovial sarcoma . J Pathol 2000 ; 192 : 342 – 50 .
64. Horvai AE , Kramer MJ , O’Donnell R . Beta-catenin nuclear expres-
sion correlates with cyclin D1 expression in primary and metastatic
synovial sarcoma: a tissue microarray study . Arch Pathol Lab Med
2006 ; 130 : 792 – 8 .
65. Ng TL , Gown AM , Barry TS , Cheang MC , Chan AK , Turbin DA ,
et al. Nuclear beta-catenin in mesenchymal tumors . Mod Pathol
2005 ; 18 : 68 – 74 .
66. Barham W , Frump AL , Sherrill TP , Garcia CB , Saito-Diaz K , VanSaun
MN , et al. Targeting the Wnt pathway in synovial sarcoma models .
Cancer Discov 2013 ; 3 : 1286 – 301 .
67. Trautmann M , Sievers E , Aretz S , Kindler D , Michels S , Friedrichs N ,
et al. SS18–SSX fusion protein-induced Wnt/beta-catenin signaling is
a therapeutic target in synovial sarcoma . Oncogene 2013 ; 33 : 5006 – 16 .
68. Proffi tt KD , Madan B , Ke Z , Pendharkar V , Ding L , Lee MA , et al. Phar-
macological inhibition of the Wnt acyltransferase PORCN prevents
growth of WNT-driven mammary cancer . Cancer Res 2013 ; 73 : 502 – 7 .
69. Rosenbluh J , Wang X , Hahn WC . Genomic insights into WNT/beta-
catenin signaling . Trends Pharmacol Sci 2014 ; 35 : 103 – 9 .
70. Michels S , Trautmann M , Sievers E , Kindler D , Huss S , Renner M ,
et al. SRC signaling is crucial in the growth of synovial sarcoma cells .
Cancer Res 2013 ; 73 : 2518 – 28 .
71. Mora-Blanco EL , Mishina Y , Tillman EJ , Cho YJ , Thom CS , Pomeroy
SL , et al. Activation of beta-catenin/TCF targets following loss of the
tumor suppressor SNF5 . Oncogene 2014 ; 33 : 933 – 8 .
72. Teng HW , Wang HW , Chen WM , Chao TC , Hsieh YY , Hsih CH , et al.
Prevalence and prognostic infl uence of genomic changes of EGFR
pathway markers in synovial sarcoma . J Surg Oncol 2011 ; 103 : 773 – 81 .
73. Bozzi F , Ferrari A , Negri T , Conca E , Luca da R , Losa M , et al. Molecu-
lar characterization of synovial sarcoma in children and adolescents:
evidence of akt activation . Transl Oncol 2008 ; 1 : 95 – 101 .
74. Setsu N , Kohashi K , Fushimi F , Endo M , Yamamoto H , Takahashi
Y , et al. Prognostic impact of the activation status of the Akt/mTOR
pathway in synovial sarcoma . Cancer 2013 ; 119 : 3504 – 13 .
75. Kang MH , Reynolds CP , Maris JM , Gorlick R , Kolb EA , Lock R , et al.
Initial testing (stage 1) of the investigational mTOR kinase inhibitor
MLN0128 by the pediatric preclinical testing program . Pediatr Blood
Cancer 2014 ; 61 : 1486 – 9 .
76. Antonescu CR , Kawai A , Leung DH , Lonardo F , Woodruff JM , Healey
JH , et al. Strong association of SYT-SSX fusion type and morphologic
epithelial differentiation in synovial sarcoma . Diagn Mol Pathol
2000 ; 9 : 1 – 8 .
77. Krskova L , Kalinova M , Brizova H , Mrhalova M , Sumerauer D , Kodet
R . Molecular and immunohistochemical analyses of BCL2, KI-67, and
cyclin D1 expression in synovial sarcoma . Cancer Genet Cytogenet
2009 ; 193 : 1 – 8 .
78. Jones KB , Su L , Jin H , Lenz C , Randall RL , Underhill TM , et al.
SS18–SSX2 and the mitochondrial apoptosis pathway in mouse and
human synovial sarcomas . Oncogene 2013 ; 32 : 2365 – 71 .
79. Kawaguchi S , Tsukahara T , Ida K , Kimura S , Murase M , Kano M , et al.
SYT-SSX breakpoint peptide vaccines in patients with synovial sar-
coma: a study from the Japanese Musculoskeletal Oncology Group .
Cancer Sci 2012 ; 103 : 1625 – 30 .
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