Poorly Differentiated Synovial Sarcoma: A Case Report
Francesco CAPPELLO,1,2M BELLAFIORE,2F BUCCHIERI,2,3G BALSANO,4A PALMA,2G ZUMMO,2
1Institute of Pathological Anatomy, 2Institute of Human Anatomy, University of Palermo,
3Institute of Internal Medicine and Pneumology, Ospedale v. Cervello,
4Institute of General and Endoscopic Surgery, University of Palermo, Palermo, Italy
© 2001 W. B. Saunders & Company Ltd on behalf of the Arányi Lajos Foundation 1219-4956/01/010063+04 $ 12.00/0
PATHOLOGY ONCOLOGY RESEARCH Vol 7, No 1, 2001
10.1053.paor.2001.0282 available online at http://www.idealibrary.com on
Synovial sarcoma is a relatively frequent malignant
soft tissue tumor. Commonly, this neoplasm arises in the
extremities and, less frequently, in parapharyngeal
region, abdominal wall or other extraarticular sites.
While the name implies an origin from synovia, general-
ly it arises in sites devoid of normal synovium. In fact, it
is thought to originate from primitive pluripotential mes-
Generally, the microscopic pattern is the classic bipha-
sic type. Nevertheless, synovial sarcoma can be charac-
terised by a predominant monophasic spindle or, more
rarely, epithelial pattern, or by a poorly differentiated
aspect. The latter is the variant with the poorest progno-
sis. Therefore, three patterns of poorly differentiated syn-
Received: July, 12, 2000; revised: Jan 10, 2001; accepted: Jan 21,
Correspondance: Franceso CAPPELLO, M.D., Via Alla Falconara
120, 90136 Palermo, Italy; Tel: +39-0339-5675268, fax: +39-091-
6553508; email: FRANCAPP@HOTMAIL.COM
Poorly differentiated synovial sarcoma is a rare soft
tissue tumor. We studied a case arising in the pleur-
al cavity of a young subject, characterised by the
presence of spindle cell, small cell, and large epithe-
lioid cell areas. We performed stains for mucosub-
stances and analysed the expression of cytokeratins
5/6, 7, 8, 18, 19, CEA, CD34, Ber-Ep4 and calretinin to
characterize the phenotype of this neoplasm. We fur-
thermore assessed immunohistochemically the pres-
ence of p53, Bcl-2, Bax and caspase 3, four apoptotic
markers, to evaluate a relationship between apoptot-
ic activity and the behaviour of this tumor. Our find-
ings showed a strong presence of calretinin, p53 and
Keywords: synovial sarcoma, poorly differentiated synovial sarcoma, soft tissue tumors, calretinin, apoptosis
Bcl-2 in all three areas. The possibility that poorly
differentiated synovial sarcoma could be calretinin-
positive was a new data, to our knowledge, and it
could be of some importance in diagnostic patholo-
gy. Moreover, the negligible positivity for Bax and
caspase 3 suggested that the minor role of pro-
grammed cell death could be one of the causes of the
aggressive behaviour of this tumor. These data also
suggest that the reduction of apoptotic phenomena
in poorly differentiated synovial sarcoma could be
considered one of the major mechanisms of tumoral
growth. (Pathology Oncology Research Vol 7, No 1,
ovial sarcoma (PDSS) have been recognised: spindle
cells (herringbone pattern), large epithelioid cells and
The differential diagnosis includes a variety of soft tis-
sue sarcomas, as malignant peripheral nerve sheath
tumors, fibrosarcomas and leiomyosarcomas. The histo-
logic criteria have been well characterised7, but sometimes
histologic and immunohistochemical aspects can make the
We therefore aimed to study histochemically and
immunohistochemically a case of PDSS. We selected dif-
ferent histochemical stains and immunohistochemical
markers, present in literature, to address the diagnosis. We
also assessed the presence of some apoptotic markers to
evaluate the role of apoptosis in the pathogenesis and in
the behaviour of this neoplasm.
Materials and Methods
We studied a case of PDSS arising in the lower right
pleural cavity of a 33-years old non-smoking man. Diag-
nosis was made using traditional techniques (H&E), histo-
chemistry and immunohistochemistry. We used 7-µm
paraffin sections. Histochemical stains for reticulin, PAS
(with and without diastase digestion), mucicarmine and
alcian blue (with and without hyaluronidase digestion)
were performed. Immunostaining by avidin-biotin com-
plex method was performed (DAKO, LSAB2), using pri-
mary antibodies against cytokeratin (CK) 5/6 (Boehringer-
Mannheim, monoclonal, 1:25), CK7 (DAKO, monoclonal,
1:100), CK8 (Sigma, monoclonal, 1:100), CK18 (Sigma,
monoclonal, 1:500), CK19 (DAKO, monoclonal, 1:50),
CEA (DAKO, monoclonal, 1:50), CD34 (DAKO, mono-
clonal, 1:40), Ber-Ep4 (DAKO, monoclonal, 1:20), calre-
tinin (Zymed, polyclonal, 1:20), p53 (Biogenex, mono-
clonal, 1:100), Bcl-2 (DAKO, policlonal, 1:10), Bax (Bio-
genex, monoclonal, 1:30), caspase 3 (Pharmingen, poly-
clonal, 1:500) and isotype-matched control. Diaminoben-
zidine (DAB chromogen, DAKO) was used as develop
Fifty percent of the tumor was composed of spindle cell
areas, with a herringbone pattern (Figure 1a). Further-
more, these areas showed a high mitotic rate and, focally,
necrosis. Moreover, the neoplasm consisted of small cell
(Figure 1b) and large cell (Figure 1c) areas. Small cell
areas showed cells with less cytoplasm and rounded
nuclei. By contrast, in the large cell areas, the nuclei had
an irregular contour and cytoplasm was increased, giving
an epithelioid appearance to the cells.
This sarcoma was positive for reticulin. In particular, the
small cell component of tumor was abundantly positive.
Moreover, the neoplasm showed PAS-positive, alcian blue
positive and mucicarmine negative mucosubstances,
inside and among the tumoral cells. PAS and alcian blue
positivity was respectively diastase and hyaluronidase
resistant (data not shown).
Interestingly, calretinin was strongly present, particular-
ly in the spindle component (Figure 2a). By contrast, CKs,
CEA, CD34, and Ber-Ep4 were negative in all compo-
nents of the tumor. Furthermore, this tumor was charac-
terised by a strong presence of p53 (Figure 2b) and Bcl-2
(Figure 2c) in all components. By contrast, there was
weak positivity for Bax (Figure 2d) and a negligible pres-
ence of caspase 3 (Figure 2e), in both small and large cells
more than in herringbone areas.
PDSS is the synovial sarcoma with the poorest prog-
nosis. Differential diagnosis is often very difficult and
speculative hypotheses about the pathogenesis of these
neoplasms rarely support definite conclusions. In partic-
ular, the difficulty to study the synovial sarcoma lies not
only in the morphologic aspect, but also in the variabili-
ty of the site. Nevertheless, the simultaneous presence of
all three patterns (herringbone, large epithelioid cells and
small cells) wakes the diagnosis.
Histochemical and immunohistochemical studies often
can not produce a reliable diagnosis without risks and,
sometimes cytogenetic studies are indispensable. Histo-
chemical positivity is a characteristic of these tumors. In
particular, synovial sarcoma is generally PAS and/or
mucicarmine and/or alcian blue positive, diastase/hyalu-
ronidase resistant. This resistance to digestion can be dis-
criminative in differential diagnosis between these and
other sarcomatoid tumors, as malignant mesothelioma.10
We performed the diagnosis using the histological crite-
ria and the histochemical results more than the immuno-
histochemical data. In particular, this case was PAS/alcian
blue positive, digestion resistant, but mucicarmine nega-
tive. This fact confirmed the importance of performing all
three mucosubstances staining to increase the diagnostic
Concerning of immunohistochemical studies, there are
many publications about the use of antibodies to diagnose
PDSS. Generally, CKs and CEA are positive in 50-100%
of cases.1,5,8,9This may be of some utility in a differential
diagnosis between this entity and others round cell sarco-
mas, such as primitive neuroectodermal tumors and malig-
nant nerve sheath tumors. Conversely, positivity to CD34
and Ber-Ep4 is less frequent.1,20,22,24
Calretinin is a recent immunohistochemical marker for
mesothelioma, but it was also found to be present in other
epithelial and spindle tumors.21In particular, biphasic syn-
64 CAPELLO et al
PATHOLOGY ONCOLOGY RESEARCH
Figure 1. a) herringbone area, H&E (25x); b) small cell area,
H&E (25x); c) large cell area, H&E (25x).
ovial sarcoma showed little positivity to this antibody.6The
importance of this datum could lie in the possibility to dif-
ferentiate the biphasic synovial sarcoma from other sarco-
mas arising in the pleural cavity, to be as, biphasic malig-
nant mesothelioma, in which, by contrast, there is a strong
presence of calretinin. This tumor was strongly positive to
calretinin; and in particular, this marker was expressed
mainly in the herringbone component. CKs, CEA, CD34
and Ber-Ep4 were absolutely negative in all areas. These
results suggested that in the presence of a strong calretinin-
positive pleural malignant tumor, the possibility of PDSS
should not be excluded in differential diagnosis.
In this PDSS, p53 was strongly positive in all compo-
nents. P53, the „guardian of genome“, is a tumor suppressor
gene. Its product is a nuclear phosphoprotein, which half-
life is normally very short. If a mutagenic agent stresses the
cell, p53 blocks the cell cycle to allow DNA repair. How-
ever, if the repair process fails, p53 induces the expression
of pro-apoptotic genes, among which is Bax, to stimulate
the apoptotic process. By contrast, when p53 is mutated, its
half-life becomes longer, it accumulates at nuclear level and
DNA-damaged cells can continue to proliferate, resulting in
tumor. Recently, Nakanishi17found that 27% of synovial
sarcoma were p53 positive and he consiclered this data
indicative of abnormal accumulation of p53. P53 presence
in this tumor could be expression of nuclear damage, but
this fact alone is not helpful in pathogenetic speculation.
Bcl-2 was also strongly positive in PDSS. Bcl-2 is a pro-
tein normally expressed in mitochondria, endoplasmic retic-
ulum and the nuclear envelope. Generally, Bcl-2 is an
homodimer that binds a pro-apoptotic protease-activating
factor (APAF-1), which is bound to a cysteine-aspartic pro-
tease, caspase 9. Bcl-2 suppresses apoptosis both prevent-
ing an increase of mitochondrial membrane permeability
(direct way) and interacting with other pro-apoptotic pro-
teins (mediated way). If DNA is irreversibly damaged, p53
induces the synthesis of Bax, which binds Bcl-2, forming an
heterodimer Bax-Bcl-2. The formation of this heterodimer
causes increased of permeability of mitochondrial mem-
branes and the release of an apoptotic trigger, cytochrome
C. The later disrupts the binding between Bcl-2 and APAF-
1 and primes the caspase cascade, inducing apoptosis.
Over-expression of Bcl-2 can inhibit apoptotic phenome-
na in vitro2. Moreover, an inverse correlation between Bcl-
2 expression and apoptotic events has been confirmed in
vivo.13,26Chilosi4found that synovial sarcoma was Bcl-2
positive. Analogously, Nicholson18and Suster25found Bcl-
2 positivity in 100% of synovial sarcomas. Segers23and
Nakanishi17found that synovial sarcoma could be also Bcl-
2 negative. In addition, Nakanishi17underlined the possibil-
ity that patients with Bcl-2 positive soft tissue tumors
showed more favourable prognosis than those Bcl-2 nega-
tive. He suggested that the immunohistochemical detection
of Bcl-2 could be useful to predict the prognosis of patients
with soft tissue tumors, as confirmed by other studies.12,14
Nevertheless, this datum was in contrast with the study of
Bubendorf3, that studied the clinical course of prostatic can-
cer and found a better prognosis in Bcl-2 negative tumors.
The strong positivity to Bcl-2 that we found in PDSS
could indicate a reduction of apoptotic phenomena and
could suggest that p53 was mutated because it could not
induce the synthesis of Bcl-2 suppressor proteins, such as
Bax. The consequent reduction of apoptosis could be a
mechanism of tumoral growth.
In addition, we found scarce positivity of Bax in PDSS.
Bax is a 21-kD molecule of a growing family of proteins
that may both promote and inhibit cell death. In particular,
Bax may overcome the death-suppressive functions of
Bcl-2.19Recently, McPake15demonstrated that Bax may
be an important determinant of chemosensitivity, propos-
ing the measurement of Bax expression as a clinical prog-
nostic indicator for tumor response to therapy. The weak
presence of Bax in PDSS could confirm the hypothesis
that this neoplasm presented a reduction of apoptotic
events as mechanism of tumoral growth. Moreover, the
contrast between the strongly positivity of p53 and the
scarce positivity of Bax suggests the hypothesis that p53 is
present but mutated.
65 Poorly Differentiated Synovial Sarcoma
Vol 7, No 1, 2001
Figure 2. a) anti-calretinin (25x); b) anti-p53 (25x); c) anti-Bcl-2 (25x); d) anti-Bax (25x); e) anti-caspase 3 (25x).
Finally, PDSS showed also scarce caspase 3 positivity. Download full-text
Caspase 3 is a member of a family of proteases that get
their name because they cleave proteins at the aspartic acid
residues. Caspases are subdivided in initiators and execu-
tors. In particular, caspase 3 belongs to the second group,
determining fragmentation of the cytoskeleton. In fact, the
sequential activation of caspases creates an expanding cas-
cade of proteolytic factors, which leads to the digestion of
structural protein of the cytoskeleton and to the degrada-
tion of chromosomal DNA in the nucleus, with the forma-
tion of apoptotic bodies and cell death.
We found negligible presence of caspase 3 in all tumoral
areas. This could be a further confirmation of the reduction
of apoptosis in this tumor.
In conclusion, our findings indicate that Bcl-2 can also
be present in the poorly differentiated variant of synovial
sarcoma. The reduction of apoptosis in this tumor could be
the mechanism of tumoral growth. Although p53 was
found strongly present, it seems not to be able to induce
the activation of apoptotic proteins, as Bax.
The continuous assembly disassembly cycle of the com-
plex network of morphologically distinct filaments and
proteins into the neoplastic mesenchymal cell11can con-
fuse histologic and immunohistochemical features in all
poorly differentiated tumors. This can explain why calre-
tinin, negligibly positive in byphasic synovial sarcoma,
can be strongly present in PDSS.
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