|
Some of the
clinical and pathological
characteristics of synovial sarcoma are given in the following tables.
|
TYPE |
MORPHOLOGIC FEATURES |
IMMUNOPHENOTYPE |
DIFFERENTIAL DIAGNOSIS |
|
Biphasic |
Presence of both spindle cell and
epithelial components |
 |
Expression of keratins (CK7 and 19
included) and/or EMA in both components in about 90% of
cases |
|
|
Expression of vimentin mostly in the
spindle cell component
|
|
|
Expression of bcl2 protein (mostly in the
spindle cell component)
|
|
|
Expression of CD99 (60-70%) |
|
|
Expression of S100 protein in up to 30%
of cases, smooth muscle alfa-actin and desmin
|
|
|
CD34 virtually always negative |
|
|
|
Carcinosarcoma |
|
|
Glandular MPNST |
|
|
Malignant mesothelioma |
|
|
Nephroblastoma |
|
|
Osteosarcoma
|
GENETICS COULD BE USEFUL IN
UNUSUAL SITES OF ORIGIN |
|
TYPE |
MORPHOLOGIC FEATURES |
IMMUNOPHENOTYPE |
DIFFERENTIAL DIAGNOSIS |
|
Monophasic
Fibrous type |
Presence of the spindle cell
component only |
|
|
Expression of keratins (CK7 and 19 included) and/or EMA |
|
|
Expression of vimentin
|
|
|
Expression of bcl2 protein |
|
|
Expression of CD99 |
|
|
Expression of S100 protein, smooth muscle alfa-actin and
desmin |
|
|
CD34 virtually always negative |
|
|
|
Fibrosarcoma |
|
|
Leiomyosarcoma |
|
|
MPNST |
|
|
SFT / hemangiopericytoma |
|
|
Spindle cell carcinoma |
|
|
Osteosarcoma
|
GENETICS COULD BE USEFUL |
|
Monophasic
Epithelial type |
Presence of the epithelial
component only |
|
|
Expression of keratins (CK7 and 19 included) and EMA |
|
|
Expression of bcl2 protein |
|
|
Expression of CD99 |
|
|
Expression of S100 protein |
|
|
CD34 virtually always negative |
|
|
|
Adenexal carcinoma |
|
|
Metastatic carcinoma |
|
|
Melanoma |
|
|
Epithelioid sarcoma |
|
|
Epithelioid MPNST |
GENETICS COULD BE REQUIRED |
|
TYPE |
MORPHOLOGIC
FEATURES |
IMMUNOPHENOTYPE |
DIFFERENTIAL
DIAGNOSIS |
|
Poorly differentiated |
It is characterized by the
presence of three histologic patterns on the basis of the cell type.
Frequently shows necrosis,
hemorrhage, and a high mitotic index
Presence of a prominent
hemangiopericytomatous pattern |
|
|
Expression of keratins (CK7 and 19
included) and EMA |
|
|
Expression of vimentin |
|
|
Expression of bcl2 protein |
|
|
Expression of CD99 |
|
|
Expression of S100 protein, smooth
muscle alfa-actin and desmin |
|
|
CD34 virtually always negative |
|
|
|
Angiosarcoma |
|
|
Organizing hemathoma |
GENETICS COULD BE REQUIRED |
|
Poorly differentiated
Large cell type |
Presence of cells that can be
larger than usual, epithelioid, sometimes with rhabdoid features,
with large nuclei and prominent nucleoli |
|
|
|
Metastatic carcinoma |
|
|
Epithelioid
sarcoma |
|
|
Rrhabdoid
tumor |
|
|
Poorly differentiated
Small cell type |
Presence of small undifferentiated
cells resembling those seen in "small round cell tumors", e.g.,
Ewing sarcoma |
|
|
|
Small round cell tumors
(ES/pPNET) |
|
|
Neuroblastic
tumors |
|
|
Rabdomyosarcoma |
|
|
Malignant
SFT / hemangiopericytoma |
|
|
Mesenchymal
chondrosarcoma |
|
|
Lymphoma |
|
|
Poorly differentiated
High grade spindle cell type |
Presence of spindle cells with
high grade features, i. e. high grade of atypia and high mitotic
index |
|
|
|
Malignant SFT /
hemangiopericytoma |
|
|
MPNST |
|
|
Other
spindle cell sarcomas |
|
Microscopic findings.
Epithelial cells.
They are characterized by true epithelial
differentiation. The neoplastic cells have large, round or oval, vesicular
nuclei and abundant cytoplasm. Their shape ranges from cuboidal to tall.
They form solid cords, nests, glands with lumina containing eosinophilic
secretions or epithelial mucin or with papillary structures. Focal squamous
metaplasia with keratinization is reported.
Spindle cells.
They are uniform and relatively small, with oval nuclei and scarce
cytoplasm, forming solid sheets.
In the poorly differentiated SS cells can
be:
|
|
Large cells, with epithelioid or
rhabdoid features |
|
|
Small round cells, as in Ewing
sarcoma/peripheral Primitive NeuroEctodermal Tumor (pPNET) |
|
|
Pleomorphic spindle cells |
Mitoses are usually scarce. The poorly
differentiated forms can show more than 2 mitoses/HPF. Necrosis is present
in poorly differentiated SS. Vascularity varies from scarce to
hemangiopericytoma-like (Figure 3).
In the less cellular areas there can be
hyalinization, myxoid changes and calcifications, with or without
ossification and rarely chondroid changes. Focal tumoral calcification, with
or without ossification, is present in about one third of SSs. In
ossifying SS the deposition of osteoid mimics an osteosarcoma. Mast
cells can be numerous.
Immunophenotype.
|
|
Cytokeratins (including CK7 and
19) are expressed in about 90% of cases, mostly in the epithelial
component. |
|
|
EMA is expressed in more then 90%
of cases, also in the spindle cell component. |
|
|
Vimentin is expressed mostly in
the spindle cell component. |
|
|
bcl2 protein is largely expressed,
mostly in the spindle cell component.
|
|
|
CD99 is expressed in about 60% of
SSs, in the cytoplasm of epithelial cells and along the cellular
membranes of spindle cells. |
|
|
S100 protein, smooth muscle
alfa-actin and desmin can be focally expressed. |
|
|
CD34 is usually negative. |
|
