Malignant rhabdoid tumor of the vulva: is distinction from epithelioid sarcoma possible? A pathologic and immunohistochemical study.

Epithelioid sarcoma (ES) and malignant rhabdoid tumor (MRT) have heretofore been regarded as two separate clinicopathologic entities. However, they have some histologic similarities, and both represent histogenetic and phenotypic enigmas. This study reports the pathologic and immunohistochemical findings of four vulvar neoplasms occurring in young women that represented diagnostic dilemmas because of their similarity to both ES and MRT. Only one case had the classic histologic features of ES, whereas, in our opinion, the other three cases fulfilled the histologic criteria of MRT, despite the fact that two of the three cases were reported earlier as examples of ES. Neither electron microscopy nor immunohistochemistry has been found to be helpful in separating ES from MRT, mainly because they share several ultrastructural and immunophenotypic features. The behavior of these vulvar tumors--ours and the few published examples of ES--is generally aggressive, more in keeping with MRT than classic ES. We believe that some, if not most, putative ES of the vulva are in fact MRT, a neoplasm with an unfavorable prognosis.