Malignant rhabdoid tumors of the vulva versus epithelioid sarcomas: a clinicopathologic, immunohistochemical, and molecular genetics study.

It has been suggested that most, if not all, extrarenal rhabdoid tumors of the vulva represent "proximal-type" epithelioid sarcomas. To better understand rhabdoid tumors of the vulva, we studied the clinicopathologic, immunohistochemical (IHC), and molecular features of 8 of these tumors and 13 extragenital epithelioid sarcomas. IHC analysis for cytokeratin AE1/AE3, EMA, S100, CD34, ERG, smooth muscle actin, desmin, and SMARCB1 (INI1) was performed. Ultrastructural study was done in one vulvar rhabdoid tumor. Next-generation sequencing of the SMARCB1 gene was performed in all cases. The 8 vulvar tumors occurred in adult women (mean age, 49 years). They were poorly differentiated neoplasms with a rhabdoid morphology. The ultrastructural study showed large amounts of intermediate filaments (10 nm). All cases had loss of expression of INI1 and were negative for CD34 and ERG. One case showed 2 SMARCB1 mutations: c.592C>T in exon 5 and c.782delG in exon 6. Follow-up revealed that 4 patients died of disease, 1 was alive with disease, and 3 were alive without evidence of disease. Epithelioid sarcomas occurred in young adults (mean age, 41 years), mostly men. Seven tumors arose in the distal extremities and the other 6 had a proximal location. They showed the characteristic "granulomatous" arrangement of the neoplastic cells. The recurrent tumors were more proximal and often showed a rhabdoid morphology. All cases had loss of expression of INI1. CD34 and ERG were expressed by 8 (62%) and 5 (38%) tumors, respectively. No SMARCB1 mutations were encountered. Follow-up revealed that 5 patients died of disease, 1 was alive with disease, and 7 were alive without evidence of disease. Based on their different morphology and biological behavior, we conclude that rhabdoid tumors of the vulva and epithelioid sarcomas are different diseases with distinct clinicopathologic features. Undifferentiated vulvar tumors with rhabdoid morphology should be classified as malignant rhabdoid tumors, rather than "proximal-type" epithelioid sarcomas.