Epithelioid sarcoma was named in 1970 in a classic paper by Enzinger, who expanded the observations in a larger series in 1985. He defined a
sarcoma with a peak incidence in young adult males and a predilection for extremities, involving subcutis or deeper tissue and extending along tendon sheaths or aponeuroses. The
tumor forms nodules with central
necrosis surrounded by bland polygonal cells with eosinophilic cytoplasm and peripheral spindling. Fibromalike, angiomatoid, and proximal aggressive variants (with larger cells, prominent nuceloi, and rhabdoid change) have since been described.
Epithelioid sarcomas regularly express
vimentin, cytokeratins, and
epithelial membrane antigen, and about half are positive for CD34, but a wide range of other
antigens can be expressed.
S100 protein,
desmin, and FLI-1 are usually negative. The ultrastructure displays epithelial and mesenchymal features including myofibroblastic differentiation. There are no specific genetic findings but several cases display
chromosomal abnormalities in the 22q region. The
tumor has no normal cellular counterpart and differs from both
synovial sarcoma and
carcinoma. There is a wide differential diagnosis from numerous benign and malignant conditions, including
granuloma annulare,
melanoma, and epithelioid
vascular neoplasms.
Epithelioid sarcoma has a high recurrence rate, which can be reduced by adequate surgery, and up to 40% metastasize, to regional lymph nodes, to lung, and other locations including scalp. Adverse prognostic factors include large size, male sex, older age,
necrosis, vascular invasion, rhabdoid cytomorphology, and inadequate excision. Thirty-six years after Enzinger's original account,
epithelioid sarcoma remains a clinically and pathologically distinct, indolent but aggressive
sarcoma of indeterminate lineage.