Epithelioid sarcoma: An immunohistochemical analysis of 112 classical and variant cases and a discussion of the differential diagnosis

Epithelioid sarcoma (ES) is a distinctive soft tissue neoplasm with a predi lection for the distal extremities of young adults. This tumor typically co ntains nodular aggregates of epithelioid and spindle cells with zonal necro sis. The neoplastic cells are generally reported to coexpress keratin and v imentin and are often stated to be positive for CD34. However, there is no large series with extensive immunohistochemical data, there are few data wi th regard to expression of different keratin subtypes, and there are no lar ge series discussing the epithelioid sarcoma subtypes. In the current study , we immunohistochemically evaluated 88 typical and 24 variant (8 angiomato id, 9 large cell/rhabdoid, and 7 "fibroma-like") ESs. Nearly all ESs with t ypical histology (94%) were positive for keratin 8 (K8), whereas 72% were p ositive for K19, 48% for intermediate- and high-molecular-weight keratins ( 34 beta EH12), and 22% for K7; reactivity with the latter two antibodies wa s usually seen in only a minority of tumor cells. Vimentin reactivity was p resent in all cases, EMA in 96% of cases and muscle-specific actin and CD34 were noted in 41% and 52% of the cases, respectively. A few ESs (7%) showe d focal cytoplasmic CD31 reactivity, but none exhibited a distinctive membr ane staining pattern, and examples tested for FVIIIRAg were negative. The a ngiomatoid, fibroma-like, and large cell-rhabdoid ES variants had immunohis tochemical profiles similar to the classic cases, supporting a common patho genesis;. Although not consistently expressed in ES, the presence of CD34 i s helpful in distinguishing this entity from primary and metastatic carcino mas and other sarcomas such as malignant rhabdoid tumor. (C) 1999 by W.B. S aunders Company.