Low-Grade Fibromyxoid Sarcoma and Hyalinizing Spindle Cell Tumor With Giant Rosettes Share a Common t(7;16)(q34;p11) Translocation

Low-grade fibromyxoid sarcoma (LGFMS) is a rare metastasizing soft tissue tumor with deceptively bland histologic features. The hyalinizing spindle cell tumor with giant rosettes (HSCT) is thought to be a closely related tumor differing only by the presence of collagen rosettes. We report the occurrence of a common t(7;16)(q34;p11) translocation in 2 cases of HSCT and 2 cases of LGFMS, thereby providing the first cytogenetic proof that LGFMS and HSCT are variants of the same entity. The tumors occurred in the thighs of 2 females and in the buttock and supraclavicular fossa of 2 males. One HSCT had a spectrum of unusual histologic features, including the presence of plump epithelioid cells with abundant cytoplasm and strands and nests of clear epithelioid cells separated by eosinophilic hyalinized stroma. Two cases showed a hitherto unreported, focal staining with epithelial membrane antigen, thus adding to the immunohistochemical profile of these tumors. LGFMS and HSCT probably have a wider spectrum of morphologic features than previously thought, the awareness of which will help pathologists to avoid diagnostic pitfalls. Demonstration of the t(7;16)(q34;p11) translocation will help to diagnose difficult cases with unusual histologic features.