Download The following cell type-specific IHC markers can be useful in the

S PINDLE C ELL T UMOR / S ARCOMA S UBTYPING
S PINDLE C ELL T UMOR / S ARCOMA S UBTYPING
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ubtyping of spindle cell tumors and sarcomas requires integration of histology, clinicopathologic parameters,
and results of IHC and/or FISH studies. Three subgroups of spindle cell tumors/sarcomas can be identified:
1. Tumors showing cell-specific differentiation (e.g., leiomyoma/ leiomyosarcoma, peripheral nerve sheath tumors)
2. Sarcomas with specific translocations (e.g., PNET/Ewing sarcoma, synovial sarcoma)
3. Sarcomas with single gene alterations, i.e., mutations, deletions, and amplification (e.g., rhabdoid tumor, dedifferentiated
liposarcoma, etc.)
Markers of nerve sheath differentiation: The principal markers of nerve sheath differentiation are antibodies to S100
protein and the p75-NTR nerve growth factor receptor. They are most helpful in confirming the diagnosis of benign and malignant
nerve sheath tumors. None of these markers, however, is specific for nerve sheath differentiation and must be used in combination
with other markers. p75-NTR is also an excellent marker of spindle cell and desmoplastic melanomas, which are generally negative for
expression of melanoma-specific antigens.
IHC studies are most efficacious in identifying group 1, while a combination of IHC and FISH studies, or sometimes FISH studies
alone, are most efficacious in identifying the latter two groups.
The following cell type-specific IHC markers can be useful in the identification of sarcomas showing
cell-specific differentiation:
Markers of epithelial differentiation in soft tissue tumors: Some sarcomas display true epithelial differentiation
(e.g., synovial sarcomas and epithelioid sarcomas) and concomitant cytokeratin expression. Other sarcomas (e.g., leiomyosarcomas,
melanomas, and angiosarcomas) can display ‘anomalous’ cytokeratin expression.
Markers of smooth muscle differentiation: The principal markers of smooth muscle differentiation are antibodies to the
intermediate filament, desmin, and to muscle-specific actin isoforms (e.g., antibodies 1A4 and HHF-35). Such antibodies are most
useful in identifying tumors such as leiomyosarcomas, although smooth muscle actin expression can be seen in other tumors showing
myofibroblastic differentiation.
H&E
p75-NTR
Case of peripheral nerve sheath tumor showing expression of the p75-NTR nerve growth factor receptor.
Markers of endothelial differentiation: Endothelial markers include von Willebrand factor (the co-factor of the clotting
factor VIII, often erroneously referred to as ‘F. VIII’), CD34, CD31, and the FLI-1 gene product, with varying sensitivities and
specificities. As a practical issue, it is best to employ both a highly specific (e.g., CD31) and a highly sensitive (e.g., FLI-1) marker to
assess the presence of endothelial differentiation in histologic and clinical settings where the diagnosis of a vasoformative tumor is
being entertained.
H&E
SM actin
A case of low-grade leiomyosarcoma showing strong expression of smooth muscle actin identified by the 1A4 clone.
Markers of myofibroblastic differentiation: Myofibroblasts are distinguished from true smooth muscle cells by their
‘partial’ muscle immunophenotype, usually smooth muscle actin positive and desmin negative. Furthermore, smooth muscle actin is
generally expressed in a characteristic peripheral, wispy pattern. Soft tissue tumors characterized by myofibroblastic differentiation
include nodular fasciitis and inflammatory myofibroblastic tumors; however, myofibroblastic differentiation can be seen in a wide
range of soft tissue tumors.
H&E
H&E
CD31
Case of spindle cell angiosarcoma showing expression of the endothelial-restricted marker, CD31.
1A4
Case of abdominal fibromatosis showing characteristic myofibroblastic differentiation, with peripheral ‘tram-tracking’ pattern
of smooth muscle actin expression.
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S PINDLE C ELL T UMOR / S ARCOMA S UBTYPING
Chromosomal Translocations
Other useful IHC markers in identifying soft tissue tumors:
Type IV Collagen: While not specific for a cell or tumor type, the presence and even pattern of expression of type IV
collagen can be helpful in identifying specific soft tissue tumor subtypes, as only a subset of sarcomas produce a type IV
collagen; furthermore, the pattern of type IV collagen expression can provide evidence to help identify selected spindle cell
tumors.
is normally a cell membrane-associated protein. However, alterations in the APC/beta catenin pathway result
in abnormal nuclear localization of this protein. Only a restricted subset of spindle cell tumors, including fibromatoses,
endometrial stromal tumors, solitary fibrous tumors, and synovial sarcomas, show this unique distribution of beta catenin.
DOG1 and CD117 (c-kit) are highly sensitive and specific markers for gastrointestinal stromal tumors. DOG1 is
particularly useful in identifying the subset of c-kit negative gastrointestinal stromal tumors (GISTs).
is a marker of a unique subset of spindle cell tumors. In addition to vascular tumors, CD34 is expressed in
dermatofibrosarcoma protuberans, solitary fibrous tumor/hemangiopericytoma, and a subset of nerve sheath tumors,
among others.
is a highly sensitive and specific marker for synovial sarcoma. This protein, initially identified with gene expression
profiling, is best used as a ‘screening marker’ for synovial sarcoma and, if positive, followed by confirmatory FISH for the
SYT translocation. Other spindle cell tumors may occasionally show high-level expression of TLE-1 such as peripheral
nerve sheath tumors.
Approximately one-third of all sarcomas contain chromosomal translocations which result in the juxtapositioning of two different
genes (one from each translocation partner) that form a ‘fusion gene’. An example is the EWSR-WT1 fusion which results from the
t(11;22)(p13;q12) translocation found in desmoplasic small round cell tumor. For detection of these translocations in tissue sections
of the tumor, two different types of probes or probe sets can be employed: (a) dual fusion, dual color FISH probes, which identify the
chromosomes participating in the translocation; a ‘positive’ result is one in which normally disparate red and green signals ‘fuse’ as a
result of the translocation into a single yellow spot; (b) breakapart probes, in which two different-colored probes span the expected
breakpoint region in one of the partner genes, with a ‘positive’ result yielding disparate (e.g., red and green) spots that would normally
be a single yellow spot.
FISH for SYT translocations of synovial sarcoma: The histologic diagnosis of synovial sarcoma can be difficult as these
tumors often resemble other spindle cell sarcomas. IHC studies are usually helpful in characterizing these tumors, but many of the
marker studies (TLE-1 and beta catenin) used to confirm this diagnosis are not completely specific. Translocations involving the SYT
gene on chromosome 18q11.2 are unique to, and ultimately define, synovial sarcomas, and confirmation of this diagnosis can be made
with high sensitivity and specificity using dual color, ‘breakapart’ FISH studies. In these assays, translocations involving the SYT gene
lead to a breakapart of the normal red-(yellow)-green overlapping signal, resulting in distinct red and green signals, as illustrated below,
which confirm the presence of the SYT translocation characteristic of synovial sarcoma.
is a tumor supressor gene product, the loss of which has been found to be a characteristic finding of the following
tumors: rhabdoid tumors, atypical teratoid/ rhabdoid tumors of the CNS, epithelioid sarcoma, MPNST, myxoid
chondrosarcoma, and soft tissue myoepitheliomas.
is the glycoprotein to which the monoclonal antibody HMB-45 is directed. In addition to being a marker of
melanoma and clear cell sarcoma, gp100 expression also characterizes the group of tumors known as PEComas (PEC =
perivascular epithelioid cell), a family of spindle to epithelioid tumors that includes angiomyolipoma, sugar tumor of the
lung, pulmonary lymphangioleiomyomatosis, clear cell myomelanocytic tumor of the falciform ligamentum teres, and
others.
H&E
Monophasic synovial sarcoma
Beta catenin
TLE-1
CD117 (c-kit)
Nuclear localization of beta catenin is a
characteristic feature of the cells of abdominal
fibromatosis.
Synovial sarcoma showing uniform
expression of the nuclear protein, TLE-1.
Strong uniform expression of c-kit in a case of
gastrointestinal stromal tumor.
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© 2013 PhenoPath Laboratories, PLLC. All rights reserved.
FISH for translocations of the SYT gene
characteristic of synovial sarcoma
TUMOR
TRANSLOCATION
FUSION GENE
FORMED
TYPE
Alveolar
rhabdomyosarcoma
t(2;13)(q35;q14)
PAX3-FOXO1
Breakapart (FOXO1)
Angiomatoid fibrous
histiocytoma
t(12;22)(q13;q12)
t(2;22)(q33;q12)
t(12;16)(q13;p11)
EWSR-ATF1
EWSR-CREB1
FUS-ATF1
Breakapart (EWSR)
Breakapart
(FUS)
Desmoplastic small
round cell tumor
t(11;22)(p13;q12)
EWSR-WT1
Breakapart (EWSR)
PNET/Ewing sarcoma
t(11;22)(q24;q12)
t(21;22)(q24;q12)
t(7;22)(q22;q12)
and others
EWSR-FLI-1
EWSR-ERG
EWSR-ETV1
EWSR partner for most
Breakapart (EWSR)
Extraskeletal myxoid
chondrosarcoma
t(9;22)(q22;q12)
EWSR-NR4A3
Myxoid/round cell
liposarcoma
t(12;16)(q13;p11)
t(12;22)(q13;q12)
FUS-DDIT3
EWSR-DDIT3
Breakapart FUS
Breakapart EWSR
Synovial sarcoma
t(X;18)(p11.2;q11.2)
SS18-SSX1
SS18-SSX2
SS18-SSX4
SYT breakapart
Breakapart (EWSR)
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