Sclerosing Epithelioid Fibrosarcoma–A Report of Two Cases with Cytogenetic Analysis of FUS Gene Rearrangement by FISH Technique

Sclerosing epithelioid fibrosarcoma (SEF) is a rare soft tissue sarcoma. Recently, a link has been suggested between SEF and low-grade fibromyxoid sarcoma (LGFMS) on the basis of the finding of the characteristic translocation t(7;16) ( FUS-CREB3L2 ) of LGFMS in a small number of studied cases of SEF. The frequency of this translocation in SEF is still unknown. We present 2 cases of SEF with cytogenetic analysis for FUS rearrangement. The tumors occurred in 12 and 58 year old patients, respectively and consisted of a well to partially circumscribed, non-encapsulated mass, comprising monomorphic, polygonal cells arranged in aggregates, cords and single file arrays in a variably sclerotic stroma. The cells exhibited minimal nuclear atypia with moderate amount of clear to eosinophilic cytoplasm and rare mitotic figures. One case also showed bland spindle cell areas with myxoid change, as seen in LGFMS. By immunohistochemistry (IHC), the tumor cells were diffusely positive for vimentin, focally for S-100 in 1 case and negative for cytokeratin (CK), epithelial membrane antigen (EMA), HMB-45, desmin, smooth muscle actin (SMA), H-caldesmon, Myo D-1, CD34 and CD 168. By fluorescent in-situ hybridization (FISH) technique, the case with mixed SEF and LGFMS histology was positive for FUS rearrangement. Our study reinforces the previously reported relationship between SEF and LGFMS, and suggests that SEF may represent a variant of LGFMS in at least some cases, rather than an entirely distinct fibrosarcoma variant.