Gross image of a poorly differentiated 10.5 cm synovial sarcoma from the thigh (inked on the outer surface), with solid and cystic components.
Glistening tan solid areas can be seen.
A karyotype reveals the characteristic t(x;18) translocation (see arrows).
Fascicles of spindle cells with hyperchromatic carrot-shaped nuclei form this monophasic SS.
These intersecting fascicles can have alternating zones of cellularity. A hypercellular region is seen here.
The spindle cells are fairly monotonous.
A looser, less cellular and cystic area (not to be confused with true gland formation) can be appreciated here.
In a biphasic tumor, epithelial glandular structures can be seen embedded within a cellular spindled background.
FNA (Diff-Quik) of the mass reveals uniform spindled cells.
Diffuse strong TLE1 immunostaining is a sensitive marker for SS. TLE1 expression is not entirely specific, as it may be seen in some examples of neurofibroma, schwannoma, malignant peripheral nerve sheath tumor, among others.
Synovial sarcomas are relatively common soft tissue tumors characterized by a distinctive translocation - t(x;18)(p11;q11). Despite its name, these tumors do not arise from synovial tissue. The pathogenesis is still debated. The most common locations are the lower extremity soft tissues, especially around knee and ankles. Other locations include the head and neck, abdominal wall, lungs and other viscera.
Grossly, the tumors are nonspecific tissue masses. If it grows slowly, the tumor may be multinodular and cystic with a fibrous pseudocapsule. If growing rapidly and poorly differentiated, the tumor may become hemorrhagic and necrotic (Ferrari). Calcifications are common and can be visualized on radiographs.
Synovial sarcomas can be monophasic (composed of fascicles of spindled cells with elongated carrot-shaped nuclei, arranged in zones of hyper and hypocellularity) or biphasic (includes foci of glandular differentiation). Other features seen in the monophasic variant include hemangiopericytoma-like vascular pattern and stromal calcifications (Folpe). Of note, a monophasic epithelial SS is exceptionally rare and will not be discussed any further.
In terms of IHC, SS is negative for CD34 (whereas solitary fibrous tumor is CD34 positive); SS is usually negative for S100 (whereas MPNST is positive for S100). SS may have limited expression of cytokeratins and EMA. Up to 70% of SS are positive for CD99, thus, CD99 is not a good marker to differentiate from Ewing sarcoma (Folpe). The best IHC to use would be nuclear expression of TLE1; and of course, confirmation of the t(x;18) by FISH or RT-PCR.
Usually arise in young adults (peak incidence in the 3rd decade), but can occur at any age. These tumors usually present as a painless expanding mass. SS of the head and neck may lead to compressive symptoms i.e. difficulty swallowing or breathing.
Surgery and radiation therapy allow for local control, but therapy for distant metastasis remains a problem limiting survival.
The SYT (on chromosome 18) can have several fusion partners such as SSX1 (2/3 of cases), SSX2 (1/3 of cases), SSX4 (rare). Although some studies suggest that SYT/SSX1 tumors have an improved prognosis, this was not confirmed in other studies (Folpe, Ferrari).
5 year survival for this tumor is ~55%. SS is an aggressive soft tissue tumor with frequent metastases, with lung being a common location.
→Best IHC stain is nuclear positivity for TLE-1.
→Characterized by t(x;18)
→Can be monophasic or biphasic
Ferrari A, Collini P. Synovial Sarcoma: an ESUN article. Available at sarcomahelp.org
Folpe AL, Inwards CY. Bone and Soft Tissue Pathology: Foundations in Diagnostic Pathology Philadelphia, PA: Elsevier; 2010: 298-300.