Case 142 - Discussion

Uploaded: 200710-31, Updated: 2007-11-03
 

Tumor positive for MyoD1 but negative for cytokeratin, desmin, EMA, S100 and vimentin.
 

Alveolar Soft Part Sarcoma

The Key Features

  • Principally in adolescents and young adults (15-35 year-old);

  • Lower extremities in the adults, and head and neck in infants and children;

  • Typical and constant histological findings: tumor is divided into groups/compartments by dense fibrous trabeculae; the tumor nests in each group are separated by thin-walled, sinusoidal vascular channels; a psendoalveolar pattern is commonly seen; individual cells are large, round/polygonal with little variation in size and shape, and have abundant, granular, eosinophilic and occasionally vacuolated cytoplasm.

  • Positive for vimentin, MSA and desmin, but negative for cytokeratin, EMA, neurofilament, GFAP, synaptophysin, myoglobin, myogenin;

  • Cytoplasmic rhomboid/rod shaped crystals by PAS stain and EM.

CLINICAL FEATURES
 

  • Rare malignant soft tissue tumor of uncertain nature; 0.4-1.0% of all soft tissue sarcoma;

  • Principally in adolescents and young adults, 15-35 years of age;

  • Locations: adults, lower extremities, especially buttock/thigh (39.5%) and leg/popliteal (16.6%); infants and children, often in the head and neck, especially the orbit and tongue;

  • Slowly growing, painless, hypervascular.

GROSS FINDINGS
 

  • Poorly circumscribed, soft, friable, yellow-white to gray-red cut surface;

  • Often large areas of hemorrhage and necrosis;

  • Frequently surrounded by numerous tortuous vessels of large caliber.

MICROSCOPIC FINDINGS
 

  • The microscopic picture varies little and is constantly typical;

  • Architectural findings: dense fibrous trabeculae of varying thickness divide the tumor into compact groups/compartments of irregular size, which in turn are subdivided into sharply defined nests/aggregates; The tumor nests are separated from each other by thin-walled, sinusoidal vascular channels that are lined by a single layer of flattened endothelial cells; In each tumor nests/groups, the center frequently exhibits degeneration, necrosis and dyshesion, which results in a psendoalveolar pattern; The tumor cells may form uniform sheets of solid /compact pattern without nested pattern, which is more common seen in infants and young children and associated with a better prognosis;

  • Cytological findings: individual cells have distinct cell borders and are large, round/polygonal with little variation in size and shape; abundant cytoplasm, granular, eosinophilic, occasionally vacuolated; one or more vesicular nuclei with small nucleoli;

  • At the margin of the tumor, there are commonly numerous dilated veins; vascular invasion is a constant and striking finding.

DIFFERENTIAL DIAGNOSES
 

  • RCC: glycogen+, crystals-, EMA+;

  • Paraganglioma: glycogen-, crystals-, synaptophysin+, chromogranin+, S100 in sustentacular cells;

  • Granular cell tumor: glycogen-, crystals-, S100+.

IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS
 

  • PAS-D staining reveals intracellular glycogen and rhomboid/rod shaped crystals. Presented at about 80% cases;

  • Negative marker: cytokeratin, EMA, neurofilament, GFAP, synaptophysin, myoglobin, myogenin;

  • Occasionally positive: S100, NSE;

  • Commonly positive: vimentin, MSA, desmin.

ELECTRON MICROSCOPIC FINDINGS
 

  • Rhomboid, rod shape or spicular crystals with a regular lattice pattern.

CYTOGENETIC STUDIES
 
  • No consistent findings

TREATMENT AND PROGNOSIS
 

  • Most important parameters, age at diagnosis, tumor size and metastasis;

  • 5-year survival, 60-67%.

REFERENCES
 

  • Enzinger and Weiss's Soft Tissue Tumors, 4th Edition. By Drs. Sharon Weiss and John Goldblum.