Epithelioid sarcoma: a clinicopathologic and immunohistochemical analysis of 106 cases from the French sarcoma group.

Epithelioid sarcoma (ES) is rare with a poor prognosis and for which a loss of INI1 expression has been recently reported. We report a study of 106 cases with clinical, histologic, and immunohistochemical data, including INI1 expression, and follow-up data. Of the 106 cases, 70 were the conventional subtype and 36 the large cell subtype. INI1 was negative in 86 cases (81.1%): 57 (81%) of 70 conventional and 29 (81%) of 36 large cell subtypes. Treatment modalities were available for 76 and follow-up for 80 patients. Of the 80 patients, 43 (54%) experienced metastasis and 25 (31%) died of the disease. Univariate analysis indicated that tumor size and mitotic index were significant for metastasis-free survival, whereas proximal location, tumor size, tumor multifocality, and mitotic index were significant for overall survival. Loss of expression of INI1 is frequent in the conventional and large cell subtypes of ES and can be used as a diagnostic marker, but it has no prognostic impact. Epithelioid sarcoma (ES) is a rare soft tissue sarcoma first described by Enzinger1 in 1970. It typically occurs in the distal extremities of young adults as a slow-growing nodule within the dermis or subcutis or in the deep soft tissues. This conventional or distal form is composed of spindle-to-polygonal epithelioid cells arranged in nodules that commonly exhibit central necrosis.2 In 1997, a proximal form arising in the deep part of the pelvis, perineum, and genital tract and proximal extremities was described.3 It consists of large epithelioid carcinoma–like and/or rhabdoid cells and has a more aggressive clinical course than distally located tumors. Moreover, it has a possible link with malignant rhabdoid tumor. Biallelic inactivation of the SMARCBI/INI1 tumor suppressor gene located on chromosome 22 has been identified as the specific genetic event of malignant rhabdoid tumors, whatever their location.4,5 Recently, deletion of the SMARCBI/ INI1 gene with gene inactivation was reported in the proximal type of ES.6 Immunohistochemical expression of INI1 was recently studied in 260 epithelioid malignant tumors, including 96 cases of ES, and showed a loss of expression in about 90% of distal and proximal ES cases.7 We report 106 cases of ES with clinical, histologic, and immunohistochemical data, including INI1 expression, and follow-up data. Materials and Methods