Sensitivity and Specificity of USP6 Gene Break-Apart Assay and Protein Expression in Nodular Fasciitis

2013-02-03 18:38:37

Laboratory Investigations; 2013 Feb; 93:8-25

Youyuan Xu, Gustavo De la Roza, Jamie Tull, Shengle Zhang



Nodular fasciitis (NF) is a common benign mesenchymal lesion that may progress through myxoid, cellular, and fibrous phases. The differential diagnosis of NF includes many other spindle cell neoplasms and it may be misdiagnosed as a sarcoma due to its rapid growth and active mitotic activity. Recently, it was discovered that the entire coding region of ubiquitin-specific peptidase 6 (USP6), an oncogene translocated in aneurysmal bone cyst (ABC), is fused to the MYH9 promoter region in up to 92% of NFs. This finding indicates a potential application of USP6 gene expression or gene break-apart as a biomarker of NF. However, the sensitivity and specificity of USP6 as a biomarker for nodular fasciitis is not known.


USP6 protein expression was detected by immunohistochemistry (IHC) with a polyclonal antibody (1:20, Sigma-Aldrich) and the USP6 gene break-apart associated with the translocation was tested by fluorescence in situ hybridization (FISH) with a DNA probe (Empire Genomics, Buffalo, NY). The assays were performed on microarrays of paraffin embedded tissues composed of NFs (7) and other soft tissue spindle cell neoplasms including desmoid-type fibromatosis (3), solitary fibrous tumors, dermatofibromas, dermatofibrosarcomas protuberans (DFSP), myositis ossificans, neurofibromas, schwannomas, angioleiomyomas, leiomyosarcomas (LMS), low grade fibromyxoid sarcoma (LGFS); and ABCs (9 primary and 2 secondary).


IHC for USP6 shows weak to moderate reactivity in 6 of 7 (86%) NFs; strong reactivity in 9 of 9 (100%) primary ABCs; variable reactivity in 5 of 6 (83.3%) LGFMSs, 3 of 3 (100%) DFSPs, 2 of 2 (100%) leiomyosarcomas, and 2 of 2 (100%) secondary ABCs. FISH for USP6 was positive in 2 of 7 (28.5%) NFs and negative in all other spindle cell neoplasms (39), including 5 cases of LGFSs and 3 cases of DFSPs that were positive by IHC. Only 3 of 11 ABCs had enough material left in tissue microarrays to perform FISH, 1 of 2 primary ABCs was positive and 1 secondary ABCs was negative. The sensitivity and specificity of USP6 for the diagnosis of NF is 86% and 20% and 29% and 100% for IHC and FISH, respectively.


Despite its low sensitivity, the use of a USP6 gene break-apart rearrangement FISH probe seems highly specific for NF and could potentially be used as an aid in its diagnosis. In contrast, USP6 IHC seems highly sensitivity but not specific for NF and its use as an ancillary test in the diagnosis of NF is not warranted.

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