NovelEIF5A-USP6Gene Fusion in Nodular Fasciitis Associated With Unusual Pathologic Features: A Report of a Case and Review of the Literature

摘要

Nodular fasciitis (NF) is a benign self-limiting soft tissue lesion that has long been considered a reactive process. Recently, however, theUSP6gene rearrangement has been discovered, and the neoplastic nature of this tumor was suggested. Since then, many fusion partners of theUSP6gene have been reported, with theMYH9gene as the most common. In this article, we describe a case of NF with a novelEIF5A-USP6gene fusion associated with unusual pathological features. A 41-year-old healthy woman with a painful, rapidly growing subcutaneous mass on the left forearm with a size of 0.8 cm is presented. A soft tissue fragment measuring 1 cm was surgically excised. Owing to positive surgical margins, re-excision was performed, yielding another 2-cm fragment. The lesion was extensively histologically investigated. Immunohistochemical and molecular-genetic analysis, namely fluorescence in situ hybridization, next-generation sequencing, and reverse transcriptase-polymerase chain reaction, were also performed. Histology revealed a dermally located, mitotically active myofibroblastic proliferation with myxoid areas that ulcerated the overlying epidermis. One atypical mitotic figure was also found. The lesion showed positive immunohistochemical staining with smooth muscle actin, whereas S100 protein and CD34 stains were negative. Using fluorescence in situ hybridization, theUSP6gene rearrangement was detected and subsequent analysis using the Archer fusionPlex Sarcoma kit revealed a novelEIF5A-USP6gene fusion. In the appropriate clinicopathological context, the detection ofUSP6gene rearrangement is extremely useful when diagnosing NF, significantly reducing the risk of misdiagnosis and inappropriate overtreatment.