Epithelioid sarcoma

Epithelioid sarcoma
Micrograph of an epithelioid sarcoma. H&E stain.
Specialty	Oncology

Epithelioid sarcoma is a rare soft tissue sarcoma arising from mesenchymal tissue and characterized by epithelioid-like features. It accounts for less than 1% of all soft tissue sarcomas. It was first definitively characterized by F.M. Enzinger in 1970.^[1] It commonly presents itself in the distal limbs (fingers, hands, forearms, or feet) of young adults as a small, soft mass or a cluster of bumps. A proximal version has also been described, frequently occurring in the upper extremities.^[2] Less commonly, cases are reported in the pelvis, vulva, penis, and spine.

Histologically, epithelioid sarcoma forms nodules with central necrosis surrounded by bland, polygonal cells with eosinophilic cytoplasm and peripheral spindling.^[3] Epithelioid sarcomas typically express vimentin, cytokeratins, epithelial membrane antigen, and CD34, whereas they are usually negative for S100, desmin, and FLI1 (FLI-1).^[3] They characteristically lack the protein INI1 (see below). Epithelioid sarcomas typically stain positive for CA125.^[4]

Epithelioid sarcoma most commonly strikes young adults, yet no age group is immune. The disease has a tendency to develop local recurrences and metastasis thereafter to regional lymph nodes, lung, bone, brain, and other locations.^[3] Generally speaking, epithelioid sarcoma has a high rate of relapse after initial treatment and tends to recur locally or regionally (at or near the original tumor site). Epithelioid sarcoma also demonstrates lymphatic spread (in 22-48% of cases), and metastasis (in 21-63% of cases).^[5] These events, as well as advanced stage (progression) and grade (aggressiveness), are predictive of an overall worse outcome. Associated with a more positive outcome are younger age, female vs. male sex, distal vs. proximal location, smaller tumor size, and negative margins upon tumor resection.^[1][6][7]