Case 154 - Discussion

Uploaded: 2007-12-06, Updated: 2007-12-30

Desmin (Previous specimen) SMA (Previous specimen)
Vimentin (Previous specimen) CK-AE1/3 (Previous specimen)
   
   
CD34 (Recent specimen) BCL2 (Recent specimen)
CD99 (Recent specimen) CK AE1/3 (Recent specimen)
 
EMA (Recent specimen)  
  • Previous specimen shows epithelial components and focal hyalinization;
  • Second specimen does not contain epithelial component and hyalinization.
  • FISH CYTOGENETICS REPORT: Molecular cytogenetic studies detected a rearrangement of the SYT region at 18q11.2 in 87% of the interphase cells from this specimen. Specifically, these results are positive for the t(X;18)(p11.2;q11.2).

Synovial Sarcoma

 

The Key Features

  • Young age, 15-40 years; most commonly close to the large joints;

  • Two different type of cells: epithelial cells and spindle cells;

  • Spindle cells: uniform, closely packed, oval dark uniform nuclei;

  • Hyalinization, calcification in 20% cases;

  • EMA+, CD99+, BCL2+, CK7+. CK19+,  CK8/18+, TLE1+;

  • t(X;18)(p11;q11). SYT-SSX1: 2/3, biphasic type, poorer prognosis; SYT-SSX2: 1/3, monophasic type, better prognosis.

CLINICAL FEATURES

  • 5-10% of all soft tissue sarcomas;

  • Mostly in the para-articular regions of the extremities (lower-60%, upper-23%), not in joint cavities or associated with synovial structure;

  • Mostly in 15-40 years, mean 34 years; M:F=1.2:1;

  • Radiology findings: round/oval, lobulated mass/swelling; calcification in 20% cases, multiple, small, spotty.

GROSS FINDINGS

  • Commonly attach to surrounding tendons, tendon sheaths, or the exterior wall of the joint capsule;

  • Sharply circumscribed, round, multilobular; complete or partial smooth, glistening pseudocapsule;

  • Section surface, yellow to gray-white;

  • Occasionally calcification present.

MICROSCOPIC FINDINGS

  • Two morphologically different type of cells:

    • Epithelial cells: in solid cords, nests or glands; cuboidal to tall and columnar; abundant pale cytoplasm; large round, oval, vesicular nuclei with distinctly outlined cellular boarders; granular or homogeneously eosinophilic secretions;

    • Spindle cells (not stroma cells): alternating darker and lighter staining regions; in solid, compact sheets/fascicles; well-oriented spindle cells of uniform appearance; small amounts of cytoplasm; oval dark nuclei with evenly dispersed, fine chromatin and inconspicuous nucleoli;

  • Commonly hyalinization (thick collagen bands separate spindle cells ), myxoid changes; calcification (20% cases); occasionally chondroid changes or ossification;

  • Mast cells infiltrate, a conspicuous feature of synovial sarcoma.

SUBTYPES

  • Biphasic type: epithelial and spindle cell components

  • Monophasic fibrous type

  • Monophasic epithelial type: very rare

  • Poorly differentiated synovial sarcoma: three patterns. 1). large cell or epithelioid pattern with prominent nucleoli; 2). small cell pattern with nuclear features similar to other small round cell tumors; and 3). high-grade spindle-cell pattern with high grade nuclear features and high mitotic index.

DIFFERENTIAL DIAGNOSES

  • Carcinosarcoma: both the epithelial and the sarcoma components show more cytological atypia;

  • Malignant mesothelioma: older male patient, asbestos exposure; gradually transition between spindle and epithelial components; WT1+;

  • Fibrosarcoma, leiomyosarcoma, and malignant peripheral nerve sheath tumor: more cytological atypia and different immunohistochemical panel;

  • Ewing's sarcoma/primitive neuroectodermal tumor: CK7-, CK19-, EWS-FLI1+

IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS

  • EMA: focally positive in 97% of cases;

  • Cytokeratin: focally positive in 69-90% of cases, the staining in epithelial cells is more prominent than in spindle cells. CK7-79%, CK19-60%, CK8/18-45%;

  • CD99: positive in 60-70% of cases;

  • BCL2: diffusely positive in all cases;

  • TLE1: positive;

  • S100: positive in 30% of cases;

  • CD34: negative

ELECTRON MICROSCOPIC FINDINGS

  • Microvilli on the surface of epithelial cells;

  • Lack of neuroendocrine secretory particles.

CYTOGENETIC STUDIES

  • t(X;18)(p11;q11): in all cases, SYT in chromosome 18, SSX1/SSX2 on Xp11)

    • SYT-SSX1: 2/3, in all biphasic type;

    • SYT-SSX2: 1/3, in vast majority of monophasic fibrous tumor;

    • SYT-SSX4: rare

  • TLE1 gene is up-regulated

TREATMENT AND PROGNOSIS

  • 5-year survival, 36-76%; up to 82% in highly calcified tumors;

  • SYT-SSX2 group has a better prognosis than SYT-SSX1 group (median overall survival, 13.7 years versus 6.1 years)

REFERENCES

  • Enzinger and Weiss's Soft Tissue Tumors, 5th Edition. By Drs. Sharon Weiss and John Goldblum. 2007.