Diagnosis, Differential ; Fasciitis/genetics* ; Fibroma ; Humans ; Panniculitis

Humans ; Fasciitis/pathology* ; Fibroma/pathology* ; Gene Rearrangement ; Proto-Oncogene Proteins/genetics* ; Ubiquitin Thiolesterase

Objective: To investigate the clinicopathological features, immunophenotypes and molecular genetics of fibroma of tendon sheath (FTS). Methods: One hundred and thirty-four cases of FTS or tenosynovial fibroma diagnosed in the Department of Pathology, West China Hospital, Sichuan University, Chengdu, China from January 2008 to April 2019 were selected. The clinical and histologic features of these cases were retrospectively reviewed. Immunohistochemistry, fluorescence in situ hybridization (FISH) and reverse transcription-polymerase chain reaction (RT-PCR) were performed on the above cases. Results: There were a total of 134 cases of FTS, including 67 males and 67 females. The patients' median age was 38 years (ranged from 2 to 85 years). The median tumor size was 1.8 cm (ranged from 0.1 to 6.8 cm). The most common site was the upper extremity (76/134, 57%). Follow-up data was available in 28 cases and there was no detectable recurrence. Classic FTS (114 cases) were well-defined and hypocellular. A few spindle-shaped fibroblasts were scattered in the dense collagenous sclerotic stroma. Characteristically elongated slit-like spaces or thin-walled vessels were observed. Most of cellular FTSs (20 cases) were well-defined and the area with increased cellularity of the spindle cells coexisted with classic FTS. There were occasional mitotic figures, but no atypical mitotic figures. Immunohistochemistry was performed in 8 cases of classic FTS and most cases were positive for SMA (5/8). Immunohistochemistry was also performed in 13 cases of cellular FTS and showed 100% positive rate for SMA. FISH was conducted on 20 cases of cellular FTS and 32 cases of classical FTS. USP6 gene rearrangement was found in 11/20 of cellular FTS. Among 12 cases of CFTS with nodular fasciitis (NF)-like morphological feature, 7 cases showed USP6 gene rearrangement. The rearrangement proportion of USP6 gene in cellular FTS without NF-like morphological features was 4/8. By contrast, 3% (1/32) of the classic FTS showed USP6 gene rearrangement. RT-PCR was performed in those cases with detected USP6 gene rearrangement and sufficient tissue samples for RT-PCR. The MYH9-USP6 fusion gene was detected in 1 case (1/8) of the cellular FTSs, while no target fusion partner was detected in the classic FTS. Conclusions: FTS is a relatively rare benign fibroblastic or myofibroblastic tumor. Our study and recent literature find that some of the classic FTS also show USP6 gene rearrangements, suggesting that classical FTS and cellular FTS are likely to be at different stages of the same disease (spectrum). FISH for USP6 gene rearrangement may be used as an important auxiliary diagnostic tool in distinguishing FTS from other tumors.
Male ; Female ; Humans ; Gene Rearrangement ; In Situ Hybridization, Fluorescence ; Retrospective Studies ; Fibroma/pathology* ; Fasciitis/genetics* ; Ubiquitin Thiolesterase ; Tendons/pathology*

OBJECTIVETo investigate the frequency of USP6 gene rearrangement in nodular fasciitis (NF) and to evaluate its clinical application.

METHODSTwenty nine cases of previously diagnosed NF were screened for the presence of the USP6 gene rearrangement by interphase fluorescence-in-situ hybridization (FISH) on formalin-fixed paraffin-embedded tissue. Fifteen of these cases, which had available tissue, were also analysed for MYH9-USP6 fusion transcripts by reverse transcription-polymerase chain reaction (RT-PCR).

RESULTSTwenty four of the 29 cases (83%) were positive for the USP6 gene rearrangement by interphase FISH. The 15 cases with RT-PCR showed the following results: 11 positive, one deletion and three negative for USP6 gene rearrangement. Of these 15 cases, eight (8/15) showed MYH9-USP6 fusion transcript by RT-PCR. Of these eight cases, seven were positive for USP6 gene rearrangement and one showed USP6 deletion by FISH.

CONCLUSIONSUSP6 gene rearrangement is a recurrent genetic event in NF. It is a valuable ancillary tool for the pathological diagnosis of these lesions.

Fasciitis ; genetics ; Gene Rearrangement ; Humans ; In Situ Hybridization, Fluorescence ; Interphase ; Proto-Oncogene Proteins ; genetics ; Reverse Transcriptase Polymerase Chain Reaction ; Translocation, Genetic ; Ubiquitin Thiolesterase ; genetics