Synovial Sarcoma Characteristics
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 |
|
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 |
|
GENETICS COULD BE USEFUL |
Monophasic Epithelial type |
Presence of the epithelial component only |
|
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 |
|
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 |
|
|
Poorly differentiated Small cell type |
Presence of small undifferentiated cells resembling those seen in "small round cell tumors", e.g., Ewing sarcoma |
|
|
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 |
|
|
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.
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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.
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Vimentin is expressed mostly in the spindle cell component.
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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.
V2N6 ESUN Copyright © 2005 Liddy Shriver Sarcoma Initiative.