Proximal-type epithelioid sarcoma in the groin presenting as a diagnostic dilemma.
ABSTRACT Epithelioid sarcoma is an uncommon soft-tissue sarcoma typically presenting as a subcutaneous or deep dermal mass in the distal extremities of young adults. Lately, a 'proximal' subtype has been described, which occurs in the pelvic and genital areas of somewhat older individuals and tends to behave more aggressively than the conventional subtype. The correct diagnosis of this subtype is essential, since this tumor can be easily mistaken for other malignant tumors that exhibit epithelioid morphology. We report a case of proximal-type epithelioid sarcoma that presented as an inguinal mass in a 47-year-old man. Histologically, the tumor consisted of diffuse sheets of epithelioid cells with scattered rhabdoid morphology. By immunohistochemistry, the neoplastic cells expressed cytokeratin, epithelial membrane antigen, vimentin, CD34, CD99 and showed complete loss of nuclear INI1 protein expression. Fluorescence in situ hybridization was considered borderline for 22q deletion. We present this case to emphasize the importance of diagnosing this uncommon tumor and the role of INI1 immunohistochemistry in establishing the diagnosis.