Proximal-type epithelioid sarcoma of the maxilla with metastasis to the scalp: Cytologic findings of an unusual malignant tumor.

Epithelioid sarcoma of proximal type (ESPT), a subtype of epithelioid sarcoma, is an uncommon malignant neoplasm of the soft tissue with histo- and cytologic features similar to epithelioid sarcoma, classic type and to the more commonly encountered extra-renal malignant rhabdoid tumor (EMRT). Unlike classic epithelioid sarcoma, ESPT usually involves pelvic, perineal, and genital regions and has an aggressive clinical course. Like EMRT, ESPT can have aberrations of the INI1 gene on chromosome 22q, which results in the loss of INI1 protein expression. We describe here the cytological findings of an ESPT metastatic to the scalp in a 14-year-old boy. Cytological preparations showed a discohesive population of pleomorphic ovoid to polygonal cells with large irregular nuclei and prominent nucleoli. Isolated cells with rhabdoid features were noted. These cells had abundant cytoplasm and occasional intracytoplasmic hyaline inclusions. In the light of the patient's clinical history of a known primary ESPT of the maxilla, the cytologic features were distinct enough to render a diagnosis of a metastatic lesion to the skull.