Sclerosing epithelioid fibrosarcoma of the oral cavity.

Sclerosing epithelioid fibrosarcoma (SEF) rarely occurs outside the somatic soft tissue. Until recently no consistently specific genetic alteration had been associated with SEF. Molecular testing of the FUS gene rearrangement involving chromosome 16 [at one time considered specific for low-grade fibromyxoid sarcoma (LGFMS) and its variant, LGFMS with giant collagen rosettes), may be a nonrandom abnormality in some cases of SEF.We present an example of a rare FUS-positive SEF that arose in the floor of mouth of a 56 year old male. Light microscopy, exhaustive immunohistology, and FISH examination showing chromosome rearrangement using the FUS break-apart probe led to an erroneous diagnosis of LGFMS with giant collagen rosettes. An outside expert agreed with that diagnosis citing the FISH results as confirmatory. Upon review almost 2 years later after local recurrence, the classic histopathologic features of SEF were noted instead. This example suggests that at least a subset if not most examples of SEF are part of the LGFMS "family" of neoplasms, and reiterates the value of careful histologic examination in an age of increasingly sophisticated and presumably specific molecular results.