Sclerosing epithelioid fibrosarcoma: Cytogenetic analysis of FUS rearrangement

Sclerosing epithelioid fibrosarcoma (SEF) is a rare but distinct variant of fibrosarcoma. A 43‐year‐old man presented with a lesion in his back that had been present for three years but had recently increased in size. Magnetic resonance imaging (MRI) revealed a 6‐cm sized ovoid mass showing low intensities on T1 and T2 weighted images. Histologically, the tumor was of moderate cellularity, and the cells were relatively uniform in size and shape. The cells were epithelioid, round, oval and polygonal with clear and slightly eosinophilic cytoplasm, forming nests, cords, or sheet‐like patterns with a dense collagenous and hyalinized matrix. The tumor was positive for vimentin, but negative for smooth muscle actin, desmin, HMB45, and CD34. Although the tumor showed nuclear overexpression of beta‐catenin protein, the CTNNB1 exon3 mutation was not detected. Fluorescent in situ hybridization for FUS using dual color break‐apart probes showed rearrangement of the FUS. In accordance with previous studies, our case showed positive findings of FUS rearrangement, reinforcing the notion of a close relationship between low grade fibromyxoid sarcoma and SEF.