Case Study: Case 1, femoral mass and lung mass; Case 2, femoral mass

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 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.