The Role of USP6 Gene Rearrangement by FISH Analysis in Nodular Fasciitis and Histological Mimics

Abstract Background: Nodular fasciitis (NF) is a common benign fibroblast and myofibroblast tumor. Although there have been constant concerns about its histological features and differential diagnosis, NF is still the most easily misdiagnosed mesenchymal lesions, especially over diagnosed as a sarcoma. USP6 gene rearrangement was reported recently to be a reproducible and specific gene change in NF, which strongly assists the diagnosis of NF. We aim to study USP6 Gene Rearrangement in NF and other spindle cell lesions mimicking NF, and to investigate the use of USP6 Gene Rearrangement in differentiating NF and its mimics.Methods: USP6 translocation by fluorescence in situ hybridization (FISH) was studied on 40 cases of NF and 54 cases of other spindle cell lesions (including 10 cases of spindle cell sarcoma) that mimic NF. Results: Thirty-four cases (85.5%) of NF showed USP6 gene translocation, including 10 cases which previously diagnosed or considered as malignant diseases by the referring pathologists. All of other 54 cases of spindle cell lesions were negative for USP6 translocation.Conclusions: USP6 gene rearrangement by FISH analysis is a reliable test for diagnosis of NF, and also a helpful adjunct to prevent over diagnosis of NF. Positive USP6 gene rearrangement by FISH could be a useful marker to exclude malignant lesions that mimics NF.