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An aneurysmal bone cyst (ABC) is a benign bone neoplasm that typically occurs during the first and second decades of life. ABC usually presents as a rapidly growing intramedullary expansile mass with multiple blood-filled cysts in the metaphysis of the long tubular bones. Here, we report a case of a periosteal solid ABC that was initially diagnosed as a high-grade surface osteosarcoma. A 10-year-old male was referred to our hospital for swelling and tenderness of the left upper arm. Radiography revealed periosteal mass without fluid-fluid levels. On performing open biopsy, the tumor showed hypercellular proliferation of uniform spindle to epithelioid cells with brisk mitotic activity (up to 12/2 mm 2 ) and lace-like osteoid formation, which was diagnosed as a high-grade surface osteosarcoma. After one course of chemotherapy using adriamycin and cisplatin, peripheral sclerosis was conspicuous, which led to pathological review and revision of diagnosis as "possibly osteoblastoma." The patient was disease-free for 4 years after marginal resection and curettage. Retrospective nanopore DNA sequencing unexpectedly detected a PAFAH1B1::USP6 rearrangement. The fusion gene was further validated using reverse transcription-polymerase chain reaction and the diagnosis was revised to ABC. Chromothripsis involving chromosome 17 has also been identified. Methylation analysis classified the present tumor as an ABC or non-ossifying fibroma using t-distributed stochastic neighbor embedding and unsupervised hierarchical clustering. This case report highlights the utility of nanopore DNA sequencing for soft tissue and bone tumor diagnosis., (© 2024 Wiley Periodicals LLC.)

Objective: To investigate the radiologic, pathologic, and molecular features of simple bone cysts (SBC), and their differential diagnoses. Methods: Fourteen cases of SBC were collected at the Department of Pathology, the First Affiliated Hospital of Nanjing Medical University from 2017 to 2022, and fluorescence in situ hybridization (FISH) was performed for retrospective analysis. Results: There were 14 patients, including 7 females and 7 males, with age range of 7 to 45 (median 29) years. The most common complaint was pain, including 4 cases with pathological fracture and 5 with history of previous trauma. The tumor size ranged from 3.4 to 13.5 (median 5.6) cm. The lesion involved the femur ( n= 4), humerus ( n= 5) and iliac bone ( n= 5). Radiologic diagnoses included SBC, aneurysmal bone cyst, and giant cell tumor of the bone or its combination with aneurysmal bone cyst-like region and fibrous dysplasia. Histologically, the cyst walls of the lesions were composed of fibrous tissue, fibrin-like collagen deposits, bone-like matrix and occasional woven bone. The lesional cells were spindled to ovoid, with scattered osteoclast-like giant cells, foamy histiocytes, hemosiderin deposits and cholesterol clefts. In 6 cases there were nodular fasciitis-like areas. Immunohistochemically, the spindled to ovoid cells were positive for SMA, EMA and SATB2 in varying degrees. FISH detection was performed in all 14 cases and EWSR1/FUS rearrangement were found in 9 cases. One case of FUS::NFATC2 fusion was detected by next-generation sequencing. Nine cases of SBC with the rearrangement were more cellular, and there were more mitotic figures in the recurrent FUS::NFATC2 fusion tumor. Clinical follow-up was obtained in all 14 cases with the time ranging from 5 to 105 (mean 46) months. Amongst them, the tumor with FUS::NFATC2 rearrangement had local recurrence twice after the first local excision, but had no more recurrence or metastasis 34 months after the subsequent segmental resection. The other 13 cases had no recurrence. Conclusions: EWSR1 or FUS rearrangement is most commonly identified in SBC, suggesting that SBC might be a neoplastic disease. In cases where the radiologic appearance and histomorphology are difficult to differentiate from aneurysmal bone cyst, FISH detection can aid in the definitive diagnosis.

Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ubiquitin-specific protease 6 ( USP6 ) rearrangements have been identified in aneurysmal bone cyst, nodular fasciitis, myositis ossificans, fibro-osseous pseudotumour of digits and cellular fibroma of tendon sheath. These entities show clinical as well as histological overlap, suggesting they are all clonal neoplastic belonging to the same biological spectrum and referred to as ' USP6 -associated neoplasms'. They all show a characteristic gene fusion formed by juxtaposition of the USP6 coding sequences to the promoter regions of several partner genes, leading to USP6 transcriptional upregulation., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2023. No commercial re-use. See rights and permissions. Published by BMJ.)

Purpose: Aneurysmal bone cyst (ABC) of the orbit is a very rare tumor, occurring mostly in the pediatric population, and can result in sight threatening complications and disfigurement. This review discusses previously reported cases with a focus on evolving treatment options and molecular genetics., Methods: We report the youngest case of an orbital ABC with a confirmed gene fusion: a 17-month-old girl, with confirmed FGFR-UPS6 (Fibroblast Growth Factor Receptor 1-ubiquitin specific peptidase 6/tre-2). A literature search for relevant publications on the topic was performed via Medline and PubMed, with the appropriate data extracted., Results: Thirty-two cases of orbital aneurysmal bone cyst were identified in the literature. Presentations are varied and can include pain, proptosis, decreased vision, and extraocular motility disturbance. Typical imaging and histopathology findings are discussed, in particular the usefulness of identifying USP6 gene arrangements. Treatment modalities are reviewed including surgery, embolization, and receptor activator of nuclear factor kappa-B ligand (RANKL) inhibitors. Recurrences can occur, usually within 2 years., Conclusions: Orbital ABC is a neoplasm that presents unique diagnostic and treatment challenges. Gene rearrangements can confirm primary ABC and rule out other underlying pathology. Disfigurement and sight threatening complications can occur due to both the disease process and with treatment. Outcomes may be improved with the use of systemic therapy., Competing Interests: The authors have no financial or conflicts of interest to disclose., (Copyright © 2022 The American Society of Ophthalmic Plastic and Reconstructive Surgery, Inc.)

Primary aneurysmal bone cyst, nodular fasciitis, myositis ossificans and related lesions as well as fibroma of tendon sheath are benign tumors that share common histological features and a chromosomal rearrangement involving the ubiquitin-specific peptidase 6 (USP6) gene. The tumorigenesis of this tumor spectrum has become complex with the identification of an increasing number of new partners involved in USP6 rearrangements. Because traumatic involvement has long been mentioned in the histogenesis of most lesions in the USP6 spectrum and they morphologically resemble granulation tissue or callus, we attempted to shed light on the function and role USP6 partners play in tissue remodelling and the repair process and, to a lesser extent, bone metabolism., (©The Author(s) 2023. Open Access. This article is licensed under a Creative Commons CC-BY International License.)

Background: This study aims to detect USP6 translocation in aneurysmal cysts located in the jaw and to give an overview of demographic data., Methods: The present retrospective cohort study includes 10 patients who underwent surgery due to an aneurysmal cyst of the jaw in our hospital between 2002 and 2021. Unstained formalin-fixed and paraffin-embedded tissue sections cut at 4 μm thickness were subjected to USP6 FISH testing., Results: All patients underwent surgical treatment. In four of ten patients (40%) USP-6-translocations have been found., Conclusion: Based on the study, it is hypothesized that the aneurysmal bone cyst of the jaw bone may be subject to a different pathomechanism than that of the long bones. Therefore, it seems conceivable that the primary cause of aneurysmal bone cysts in the jaw might differ., (© 2022 The Authors. Journal of Oral Pathology & Medicine published by John Wiley & Sons Ltd.)

Aneurysmal bone cyst (ABC) is a benign bone neoplasm that usually affects the metaphysis of long bones and the posterior elements of vertebral bodies. The rearrangement of USP6 gene is present in most of primary ABC cases. Synchronous polyostotic presentation is extremely rare. All of the eight reported cases in literature have a classic ABC histomorphology, including dilated-blood filled cystic spaces separated by fibrous septa and composed of variably cellular bland fibroblasts with scattered osteoclast-like giant cells and reactive new bone formation. Herein, we report a case of a 29-year-old female with a synchronous polyostotic solid variant of ABC involving her T7-T11 posterior elements of her thoracic vertebrae with a novel AHNAK::USP6 fusion, detected by next-generation sequencing (NGS). This case is distinguished by its synchronous polyostotic presentation, solid rather than classic ABC morphology and novel AHNAK::USP6 fusion, which has not been previously reported in ABC or in any mesenchymal bone tumor., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Background: Solid variant aneurysmal bone cysts (SVABCs) are a rare but well-described subtype of ABCs. While classic ABCs are readily identified radiographically, SVABCs lack these characteristic radiographic features and thus have a wide differential diagnosis on presentation (including Ewing sarcoma, Langerhans cell histiocytosis, osteosarcoma, metastasis, and giant cell tumor). Genomic/molecular analyses are often necessary for the diagnosis of SVABCs, with USP6 rearrangements being a characteristic finding. We present two cases in which genomic analysis was critical in the diagnosis of SVABCs and revealed unique gene fusions that may provide insight into SVABC pathogenesis., Case Descriptions: Two 13-year old male children presented to our institution with new mass lesions involving the craniofacial skeleton. Magnetic resonance imaging (MRI) in both cases revealed predominantly solid, avidly enhancing masses, one of the squamous portion of the temporal bone, and the other arising from the sphenopalatine foramen with extension into the ipsilateral maxillary and ethmoid sinuses. Histopathology displayed predominantly solid morphology, and next generation sequencing (NGS) revealed a FAT1-USP6 gene fusion in the temporal lesion, and a MIR22HG-USP6 gene fusion in the maxillofacial lesion, the latter of which was not identified on fluorescence in situ hybridization (FISH). These findings were most consistent with a diagnosis of SVABC in each case., Conclusions: These two cases highlight novel gene fusions in atypically located SVABCs and emphasize the ability of NGS to more accurately and consistently identify USP6 gene fusions, particularly in SVABCs that may otherwise be indistinguishable from alternative pathologies., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Epithelioid osteoblastoma, sometimes equated with aggressive osteoblastoma, is a variant of osteoblastoma that typically demonstrates more worrisome imaging and pathological features compared to conventional osteoblastoma. These more aggressive features can overlap with those seen in osteosarcoma, creating a diagnostic challenge for radiologists and pathologists. Recent identification of FOS and FOSB gene rearrangements in osteoid osteoma and osteoblastoma has allowed for greater diagnostic confidence following biopsy, but careful radiological-pathological correlation remains a key component for guiding appropriate management. Although the imaging features of conventional osteoblastoma have been previously described, there are limited examples in the literature of the imaging appearance of epithelioid osteoblastoma, and none with secondary aneurysmal bone cyst. In this case report, we detail the clinical, imaging, and histological characteristics of a proximal femoral epithelioid osteoblastoma which was pathologically confirmed by FOS and FOSB genetic testing. The initial imaging impression favored a malignancy, but when the biopsy results were correlated in a multidisciplinary fashion with the imaging, epithelioid osteoblastoma became the leading diagnosis which was subsequently genetically confirmed. This case emphasizes the value of multidisciplinary radiology-pathology correlation in routine practice., (© 2021. ISS.)

A simple bone cyst (SBC) is a cystic bone lesion predominantly affecting young males. The cyst is lined by a fibrous membrane and filled with serosanguinous fluid. EWSR1/FUS-NFATC2 rearrangements were recently identified in SBC. We here report exactly the same rearrangement in 3 lesions diagnosed as vascular malformations of 2 elderly patients. In total, through Archer FusionPlex, fluorescence in situ hybridization and/or reverse transcriptase-polymerase chain reaction the EWSR1-NFATC2 rearrangement was identified in 6 of 9 SBC, 3 of 12 benign vascular tumors, and none of 5 aneurysmal bone cyst lacking USP6 fusion. Using fluorescence in situ hybridization, it was apparent that amplification of the fusion, as seen in EWSR1-NFATC2 round cell sarcomas, was absent, and that in the vascular tumors the fusion was present both in the lining cells as well as in the surrounding spindle cells. Of note, not all of the spaces in the vascular malformations were lined by endothelial cells. Aggrecan was positive in all cases but was not specific. NKX2-2 and NKX3-1 staining were negative in all cases. Thus, even though the overlap between the 2 entities is limited to the presence of few thick-walled cysts lacking endothelial lining in the benign vascular malformations, the spectrum of benign tumors containing NFATC2 fusions should be expanded and contains not only SBC in the young, but also vascular malformation/hemangioma in elderly patients., Competing Interests: Conflicts of Interest and Source of Funding: Supported by the Netherlands Organization for Scientific Research (ZON-MW VICI 170.055 to J.V.M.G.B.). In the past, the Departments of Pathology and Cell and Chemical Biology, LUMC, received royalty payments from Kreatech/Leica for EWSR1/NFATC2 probes. The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article., (Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc.)

The term giant cell-rich tumors of bone refers to a shared morphologic pattern in a group of different osseous lesions, that is, the abundance of osteoclastlike giant cells. Fitting with a broad spectrum of clinical presentations and biological behavior, the recent detection of characteristic molecular alterations in giant cell tumor of bone (H3-3), nonossifying fibroma (KRAS, FGFR1), giant cell granuloma of the jaws (KRAS, FGFR1, TRPV4), and aneurysmal bone cyst (USP6) have contributed significantly to the biological understanding of these morphologically related but clinically distinct lesions and their systematic classification, highlighting differences and pathogenic relationships., Competing Interests: Disclosure The authors have nothing to disclose., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

Aneurysmal bone cyst is a benign bone neoplasm that most commonly arises from the metaphyses of long bones in the first and second decades of life. Here, we describe a case of an aneurysmal bone cyst that occurred in the distal tibial diaphysis of a 72-year-old female that was concerning for malignancy on imaging, demonstrating cortical breakthrough and soft tissue extension. Histologically, the tumor showed the characteristic morphologic features of aneurysmal bone cyst. Fluorescence in situ hybridization was positive for USP6 rearrangement, and RNA sequencing revealed a USP6 gene fusion with VDR, a novel partner that encodes the vitamin D receptor and that has not been implicated previously in human neoplasia. This case highlights the diagnostic challenges presented by aneurysmal bone cyst in elderly adults, and it expands the genetic spectrum of USP6 rearrangements., (© 2021 Wiley Periodicals LLC.)

Background: The rarity of juvenile psammomatoid ossifying fibroma (JPOF) and lack of cytogenetic studies prompted us to report a novel SETD2 gene mutation in a benign odontogenic tumour., Case Presentation: A 21-year-old man presented with a hard, expanded mandibular cortex. Computed tomography revealed multilocular radiopacity in the mandible; this was reconstructed via segmental mandibulectomy using a vascularised iliac crest flap. Based on the clinical and histological findings, we diagnosed JPOF associated with an aneurysmal bone cyst. Microscopically, the solid area was characterised by many rounded or angular ossicles in a cellular fibrous stroma. The stromal cells were spindle-like or stellate. Next-generation sequencing detected a frame shift mutation of the SETD2 gene, while the copy number was normal., Conclusions: Our findings suggest further genetic studies should be performed to assess whether this mutation is related to tumour genesis. ., (© 2021. The Author(s).)

Nodular fasciitis, primary aneurysmal bone cyst, myositis ossificans, and their related lesions are benign tumors that share common histological features and a chromosomal rearrangement involving the ubiquitin-specific peptidase 6 (USP6) gene. The identification of an increasing number of new partners implicated in USP6 rearrangements demonstrates a complex tumorogenesis of this tumor spectrum. In this study on a series of 77 tumors (28 nodular fasciitis, 42 aneurysmal bone cysts, and 7 myositis ossificans) from the database of the French Sarcoma Group, we describe 7 new partners of the USP6 gene. For this purpose, rearrangements were first researched by multiplexed RT-qPCRs in the entire population. A targeted RNA sequencing was then used on samples selected according to a high USP6-transcription level expression estimated by RT-qPCR. Thanks to this multistep approach, besides the common USP6 fusions observed, we detected novel USP6 partners: PDLIM7 and MYL12A in nodular fasciitis and TPM4, DDX17, GTF2I, KLF3, and MEF2A in aneurysmal bone cysts. In order to try to bring to light the role played by the recently identified USP6 partners in this lesional spectrum, their functions are discussed. Taking into account that a traumatic participation has long been mentioned in the histogenesis of most of these lesions and because of their morphological resemblance to organizing granulation reparative tissue or callus, a focus is placed on their relationship with tissue remodeling and, to a lesser extent, with bone metabolism., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.)

Context.—: Bone and soft tissue tumors are heterogeneous, diagnostically challenging, and often defined by gene fusions., Objective.—: To present our experience using a custom 34-gene targeted sequencing fusion panel., Design.—: Total nucleic acid extracted from formalin-fixed, paraffin-embedded (FFPE) tumor specimens was subjected to open-ended, nested anchored multiplex polymerase chain reaction and enrichment of 34 gene targets, thus enabling detection of known and novel fusion partners., Results.—: During a 12-month period, 147 patients were tested as part of routine clinical care. Tumor percentage ranged from 10% to 100% and turnaround time ranged from 3 to 15 (median, 7.9) days. The most common diagnostic groups were small round blue cell tumors, tumors of uncertain differentiation, fibroblastic/myofibroblastic tumors, and adipocytic tumors. In-frame fusion transcripts were identified in 64 of 142 cases sequenced (45%): in 62 cases, the detection of a disease-defining fusion confirmed the morphologic impression; in 2 cases, a germline TFG-GPR128 polymorphic fusion variant was detected. Several genes in the panel partnered with multiple fusion partners specific for different diagnoses, for example, EWSR1, NR4A3, FUS, NCOA2, and TFE3. Interesting examples are presented to highlight how fusion detection or lack thereof was instrumental in establishing accurate diagnoses. Novel fusion partners were detected for 2 cases of solid aneurysmal bone cysts (PTBP1-USP6, SLC38A2-USP6)., Conclusions.—: Multiplex detection of fusions in total nucleic acid purified from FFPE specimens facilitates diagnosis of bone and soft tissue tumors. This technology is particularly useful for morphologically challenging entities and in the absence of prior knowledge of fusion partners, and has the potential to discover novel fusion partners.

Aims: USP6 rearrangement underpins self-limiting fibroblastic/myofibroblastic neoplasms, including nodular fasciitis (NF), myositis ossificans (MO), aneurysmal bone cyst (ABC), and related variants. The aim of this study was to characterise UPS6 and fusion partners in order to delineate the clinicopathological, genetic and bone-forming features in such lesions of soft tissue (ST)., Methods and Results: Break-apart fluorescence in-situ hybridisation (FISH) validated USP6 rearrangement in 31 of 35 NF [comprising three of three fasciitis ossificans (FO) cases, seven of eight cellular variant of fibroma of tendon sheath (C-FTS), four of six MO, three of three ST-ABC, and two of two fibro-osseous pseudotumours of digits (FOPD)]. As determined with FISH and reverse transcription polymerase chain reaction, MYH9-USP6 was the commonest fusion in four C-FTS and 20 NF, including one intravascular case and two infantile (one retroperitoneal) cases. The presence of MYH9-USP6 confirmed the diagnosis of two NFs> 50 mm with prominent ischaemic necrosis. COL1A1-USP6 was predominant in ossifying lesions, including all FO, MO, ST-ABC and FOPD with identified partner genes, and was also present in non-ossifying head and neck NF (HN-NF) and C-FTS in two cases each. A cervical NF of a 14-month-old girl harboured the novel COL1A2-USP6. Ossifying lesions showed considerable genetic and morphological overlaps. Sharing COL1A1-USP6, FO and FOPD showed similar central or haphazard bone matrix deposition. Besides zonation of outward bone maturation, four COL1A1-USP6-positive MO had incipient to sieve-like pseudocysts reminiscent of ST-ABC., Conclusion: MYH9-USP6 is present in some C-FTS and most NF, including rare variants, but is unrelated to bone formation. All bone-forming USP6-rearranged lesions adopt COL1A1 as the 5' partner, indicating close genetic kinships. However, COL1A1/COL1A2 also contributes to the pathogenesis of minor subsets of non-ossifying USP6-rearranged HN-NF and C-FTS., (© 2020 John Wiley & Sons Ltd.)

A simple bone cyst (SBC) is a benign bone lesion of unknown etiology. It can be differentiated from an aneurysmal bone cyst (ABC) by radiologic and histopathologic features, as well as by the absence of fusions of the USP6 gene characteristic of an ABC. In an attempt to differentiate between ABC and SBC in a recurrent bone cyst, we performed targeted RNA sequencing and found an EWSR1-NFATC2 fusion and no fusion of the USP6 gene. We subsequently analyzed additional 10 cysts, consistent with SBCs after radiologic-pathologic correlation, for the presence of an NFATC2 gene fusion, by targeted RNA sequencing, reverse-transcription polymerase chain reaction (RT-PCR) and Sanger sequencing, and fluorescent in situ hybridization. Targeted RNA sequencing showed a FUS-NFATC2 fusion in 4 of 11 SBCs and an EWSR1-NFATC2 fusion in 2 of 11 SBCs. No fusion was identified in 3 SBCs and the analysis was not successful in 2 SBCs because of the low quantity or poor quality of isolated RNA. All the 6 fusions detected by targeted RNA sequencing were confirmed by RT-PCR and Sanger sequencing, and 5 of the 6 fusions by fluorescent in situ hybridization. An additional FUS-NFATC2 fusion was identified by RT-PCR, Sanger sequencing, and fluorescent in situ hybridization in 1 of the 3 cases negative for fusions by targeted RNA sequencing. At least a large subset of SBCs represents cystic neoplasms characterized by FUS-NFATC2 or EWSR1-NFATC2 fusions, which also define a group of distinct, rare "Ewing-like" sarcomas that predominantly arise in long bones. Our results provide additional evidence of the existence of benign lesions with FUS-NFATC2 or EWSR1-NFATC2 fusions. Although they can recur locally in a nondestructive manner, their clinical course and possible relation to sarcoma with EWSR1-NFATC2 or FUS-NFATC2 fusion remains to be elucidated.

Nearly 20 years ago, the first description of a translocation involving chromosome 17 on which USP6 resides was described. Since then, not only the culprit gene but also many fusion partners, leading to transcriptional activation of USP6 , have been detected. The first neoplasm known to harbor USP6 rearrangements was aneurysmal bone cyst. Since then, other entities like nodular fasciitis, myositis ossificans, fibro-osseous pseudotumor of digits, and a subgroup of fibromas of tendon sheath, probably representing tenosynovial nodular fasciitis, have been added to the list of USP6 -rearranged lesions. Remarkably, all of them share clinical as well as morphological characteristics, and authors have suggested that these entities actually belong to the same spectrum. This review summarizes the current knowledge regarding USP6 -rearranged lesions and further elaborates on how these neoplasms relate to one another. We propose to call these lesions UAN ( Usp6 -associated neoplasm).

Background/aim: Aneurysmal bone cyst is a benign bone lesion with a strong tendency to recur. The rearrangement of chromosome band 17p13/USP6 gene is now considered a characteristic genetic feature of aneurysmal bone cyst, with t(16;17)(q22;p13)/CDH11-USP6 as the most frequent chromosomal aberration/fusion gene. We report a novel variant translocation leading to a new fusion gene in an aneurysmal bone cyst., Materials and Methods: Genetic analyses were performed on an aneurysmal bone cyst found in the tibia of a child., Results: G-banding chromosome analysis yielded the karyotype 46,XX,t(12;17)(q21;p13)[5]/46,XX[2]. FISH analysis with a USP6 break-apart probe showed rearrangement of USP6. RNA sequencing detected LUM-USP6 and USP6-LUM fusion transcripts which were subsequently verified by RT-PCR/Sanger sequencing. The two genes exchanged 5'- non-coding exons. Thus, promoter swapping between USP6 and LUM had taken place., Conclusion: We report a novel t(12;17)(q21;p13) chromosome translocation which gave rise to a LUM-USP6 fusion in an aneurysmal bone cyst., (Copyright© 2020, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

The solid variant of aneurysmal bone cyst (SVABC) is very uncommon and frequently misdiagnosed. We reevaluated and summarized the clinicopathologic features of 17 SVABCs and further discussed the use of this nomenclature to differ SVABCs from extragnathic giant cell reparative granuloma (GCRG) in the setting of the USP6 rearrangement era. The immunohistochemical markers included α-SMA, SATB2, AE1/AE3, Ki67, S100, CD68 and P63. USP-6 status was detected by fluorescence in situ hybridization using a break-apart probe. The 17 patients with SVABCs comprised 10 males and 7 females ranging in age from 4 to 70 years. The involved locations included the long bone (n = 11), hand (n = 4), rib (n = 1) and vertebra (n = 1). The lesions were characterized by proliferated spindle cells with scattered giant cells and hemorrhages with variable positive α-SMA, SATB2, CD68 and Ki-67 expression. All patients had USP6 rearrangements without H3F3A glycine 34 mutations. Our study reveals that SVABC shares similar clinical and histologic features with other bone lesions, which may lead to an erroneous diagnosis. The presence of an USP-6 rearrangement contributes to the diagnosis SVABC; SVABC and most of the previously documented extragnathic GCRGs may be considered within the umbrella of primary aneurysmal bone cysts., (© 2020 Japanese Society of Pathology and John Wiley & Sons Australia, Ltd.)

Herein we described the clinical, radiological, histological, and molecular characteristics of seven soft tissue aneurysmal bone cysts (STABCs) diagnosed and managed at a tertiary cancer center and to elucidate their relationship with myositis ossificans (MO). All cases had established imaging and histopathological diagnosis of STABC and were subject to fluorescence in situ hybridization (FISH) for USP6 rearrangement and Archer® FusionPlex® targeted RNA sequencing (RNASeq) analysis to identify the fusion partner. A thorough literature review of STABC and MO was conducted. The patients presented with painful masses unpreceded by trauma, occurring most commonly in the deep soft tissue of the thigh/gluteus (4/7), and also in the supraclavicular region, the axilla, and the hand. On imaging, the lesions were frequently associated with peripheral calcification on conventional radiographs and CT (6/7), cystic components on ultrasound, as well as perilesional edema (7/7) and fluid levels (3/7) on MRI. Bone scan (1/1) showed intense radiotracer uptake. Histologically, 6/7 cases demonstrated zonal arrangements reminiscent of MO. USP6 rearrangement was found in all seven cases by FISH and/or RNASeq. RNASeq further detected COL1A1-USP6 fusion in six cases and a novel ANGPTL2-USP6 fusion in one case. Four patients underwent resection of the tumors and were disease free at their last follow-up. Three patients who underwent incisional or needle biopsies had no evidence of disease progression on imaging studies. In conclusion, the clinical, radiological, and pathological overlap between STABC and MO suggests that they are closely related entities. A novel fusion ANGPTL2-USP6 is associated with distinct clinical and pathological presentation.

Aneurysmal bone cyst (ABC) is a benign but locally aggressive neoplasm, with a tendency for local recurrence. In contrast to other bone tumors with secondary cystic change, ABC is characterized by USP6 gene rearrangement. There is a growing list of known USP6 fusion partners, characterization of which has been enabled with the advent of next-generation sequencing (NGS). The list of known fusion partners includes CDH11, CNBP, COL1A1, CTNNB1, EIF1, FOSL2, OMD, PAFAH1B1, RUNX2, SEC31A, SPARC, STAT3, THRAP3, and USP9X. Using NGS, we analyzed a series of 11 consecutive ABCs and identified USP6 fusions in all cases, providing further evidence that USP6 fusions are universally present in primary ABCs. We identified four novel fusion partners in five ABCs and confirmed them by RT-PCR and Sanger sequencing, ASAP1, FAT1, SAR1A, and TNC (in two cases). Because of high sensitivity and specificity, detection of a USP6 fusion by NGS may assist in differentiating between ABC and its mimics, especially in small biopsy samples when a definite diagnosis cannot be achieved on morphological grounds alone. Further studies with a large number of cases and follow-up are needed to determine whether different fusion partners are associated with specific clinical and pathologic features of ABCs., (© 2020 Wiley Periodicals, Inc.)

Aneurysmal bone cysts (ABCs) are benign lesions which most frequently occur in the long bones of pediatric patients. Long thought to be reactive, recent molecular advances have demonstrated that the majority of primary ABCs harbor rearrangements of the USP6 gene, confirming their neoplastic nature. Secondary ABCs arising from other lesions do not demonstrate this recurrent genetic anomaly. ABCs rarely occur in the craniofacial bones, and sinonasal ABCs are exceedingly rare. We report a case of a primary ABC arising the maxillary sinus of a 14-year-old female, which was found to harbor USP6 rearrangement. We describe the clinical, radiologic, and pathologic features of this case, and review the current literature on craniofacial ABCs. Careful histologic evaluation and genetic studies are warranted in order to confirm the rare occurrence of a primary sinonasal ABC.

Goals: Ubiquitin specific protease 6 ( USP6 ) gene rearrangement has been reported in approximately 70%-75% of aneurysmal bone cyst cases. We hypothesize that fluorescence in situ hybridization (FISH) testing of this marker will be useful in the pathological differentiation of primary aneurysmal bone cyst (ABC), secondary ABC, giant cell tumor of bone (GCT), and telangiectatic osteosarcoma (TOS) which are morphologically similar. This study aims to evaluate the efficacy of this test and validate it for diagnostic use., Procedures: FISH was performed in primary ABC, secondary ABC, GCT and TOS using dual color USP6 gene break apart probes. The sensitivity, specificity, positive predictive value, and negative predictive values were calculated., Results: Primary ABC demonstrates USP6 rearrangement. All secondary ABC, GCT and TOS were negative. The test sensitivity and specificity in primary ABC were 53% (9/17) and 100% (18/18), respectively. The positive predictive value and negative predictive value were 100% (9/9) and 69% (18/26), respectively., Conclusion: The USP6 gene break apart detected by FISH is validated as a novel diagnostic tool for primary ABC in our laboratory. This test could be used to study the predictive value of USP6 targeted therapy for primary ABC in the near future., (© 2019 by the Association of Clinical Scientists, Inc.)

Primary aneurysmal bone cyst (ABC) is a benign multiloculated cystic lesion of bone that is defined cytogenetically by USP6 gene rearrangements. Rearrangements involving USP6 are promoter swaps, usually generated by fusion of the noncoding upstream exons of different partner genes with exon 1 or 2 of USP6, thus leading to transcriptional upregulation of full-length USP6 coding sequence. Testing for USP6 rearrangements is used diagnostically to distinguish it from secondary ABC and other giant cell-rich primary bone tumors. In this report, we present a case of a 16-year-old male with a primary ABC of the left distal femur. USP6 break apart fluorescence in situ hybridization was positive for a rearrangement and conventional chromosome analysis identified a reciprocal X;17 translocation. In order to identify the putative USP6 fusion partner, we performed RNA sequencing and uncovered a novel USP9X-USP6 promoter swap fusion. This result was confirmed by reverse transcription-polymerase chain reaction (RT-PCR) and by mate pair sequencing thus showing the utility of these alternative methodologies in identifying novel fusion candidates. Ubiquitin-specific protease 9X (USP9X), like USP6, encodes a highly conserved substrate-specific deubiquitylating enzyme. USP9X is highly expressed in a number of tissue types and acts as both an oncogene and tumor suppressor in several human cancers. We conclude that oncogenic activation of USP6 via USP9X promoter exchange represents a novel driver of primary ABC formation., (© 2019 Wiley Periodicals, Inc.)

Primary aneurysmal bone cyst (ABC) is a cystic bone neoplasm characterized by disease-defining gene fusions involving the USP6/Tre2 gene. The literature describing gnathic ABC is limited. This case report describes a 27-year-old man presenting with a long-standing left-sided facial asymmetry. Multi-detector computed tomography imaging demonstrated a large expansile lesion positioned within the left condylar head. The lesion was biopsied and resected. The specimen showed a giant cell-rich cystic neoplasm, with fibrous tissue lined by multinucleated giant cells. Next-generation sequencing confirmed the presence of a USP6-CDH11 fusion gene, consistent with classification as a primary ABC, the first reported to be translocation-positive in the head of the mandibular condyle., (Copyright © 2018 Elsevier GmbH. All rights reserved.)

Paraspinal tumors with benign histology in the absence of trauma rarely arise in children. Treatment of such benign tumors, in contrast to malignancies, generally consists of surgical resection of the lesion with confirmation of histology via pathologic evaluation. We present a pediatric case of an atraumatic paraspinal mass with a histologic diagnosis of aneurysmal bone cyst, and USP6 gene rearrangement supporting the histologic diagnosis. The patient underwent gross total resection of the paraspinal lesion with no additional intervention. We highlight the differential diagnosis of paraspinal tumors in children and key features that led to the diagnosis in this patient.

Aneurysmal bone cyst (ABC) is a benign but locally aggressive, mostly pediatric neoplasm, with characteristic USP6 gene rearrangement that distinguishes it from a secondary ABC and other primary bone tumors. With the advent of next-generation sequencing (NGS) technology, several hitherto unknown USP6 fusion partners have been identified in ABC. Accordingly, we present a case of an 18-year-old male with a solid sub-periosteal primary ABC in the diaphysis of the left femur. Using an NGS-based assay, we identified SPARC-USP6 fusion, which has not previously been described in ABC. Including our case, the list of currently known USP6 fusion partners in primary ABC include: CDH11, CNBP, COL1A1, CTNNB1, EIF1, FOSL2, OMD, PAFAH1B1, RUNX2, SEC31A, SPARC, STAT3 and THRAP3., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Aneurysmal bone cysts (ABCs) mostly occur in the metaphysis of long bones. Primary paranasal ABCs are extremely rare, and most reported cases reveal typical histopathological features including cystic space with fibrous septa and hemorrhage. Solid-variant ABCs or solid ABCs lacking cyst formation may be histologically indistinguishable from giant cell reparative granulomas, giant cell tumor of bone, and brown tumor. Here we report the case of a 24-year-old woman with a paranasal mass diagnosed as USP6-rearranged solid ABC, mimicking giant cell reparative granuloma, giant cell tumor of bone, and brown tumor. For paranasal sinus bone or soft tissue tumors containing numerous giant cells, molecular analysis including the USP6 gene may serve as a useful diagnostic tool to distinguish solid ABCs from other giant cell-rich lesions., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Myositis ossificans is defined as a self-limiting pseudotumor composed of reactive hypercellular fibrous tissue and bone. USP6 rearrangements have been identified as a consistent genetic driving event in aneurysmal bone cyst and nodular fasciitis. It is therefore an integral part of the diagnostic workup when dealing with (myo)fibroblastic lesions of soft tissue and bone. Two cases of myositis ossificans with USP6 rearrangement were published so far. We determine herein the incidence of USP6 rearrangement in myositis ossificans using USP6 fluorescence in situ hybridization analysis (FISH). Of the 11 cases included, seven patients were female and four were male. Age ranged from 6 to 56 years (mean 27 years). Lesions were located in the thigh (n = 5), knee (n = 1), lower leg (n = 1), lower arm (n = 1), perineum (n = 1), gluteal (n = 1) and thoracic wall (n = 1). All assessable cases except one (8/9) showed rearrangement of USP6 providing evidence that myositis ossificans is genetically related to nodular fasciitis and aneurysmal bone cyst., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Small supernumerary ring chromosome 6 (sSRC[6]) is a rare chromosomal abnormality characterized by a broad clinical phenotype. The spectrum of this disorder can range from phenotypically normal to severe developmental delay and congenital anomalies. We describe two unrelated patients with small SRCs derived from chromosome 6 with a novel bone phenotype. Both patients presented with a complex bone disorder characterized by severe osteopenia, pathologic fractures, and cyst-like lesions within the bone. Imaging revealed decreased bone mineral density, mutiple multiloculated cysts and cortical thinning. Lesion pathology in both patients demonstrated a bland cyst wall with woven dysplastic appearing bone entrapped within it. In patient 1, array comparative genomic hybridization (CGH) detected a tandem duplication of region 6p12.3 to 6q12 per marker chromosome. Cytogenetic analysis further revealed a complex patient of mosaicism with some cell lines displaying either one or two copies of the marker indicative of both tetrasomy and hexasomy of this region. Patient 2 was mosaic for a sSRC that encompassed a 26.8 Mb gain from 6p21.2 to 6q12. We performed an in-depth clinical analysis of a phenotype not previously observed in sSRC(6) patients and discuss the potential influence of genes located within this region on the skeletal presentation observed., (© 2017 Wiley Periodicals, Inc.)

Differentiating osteoclast-rich lesions of bone (giant cell tumor of bone [GCTB], chondroblastoma [CBA], and aneurysmal bone cyst [ABC]) can be challenging, especially in small biopsies or fine-needle aspirations. Mutations affecting codons 34 and 36 of either H3 Histone Family Member 3A (H3F3A) and/or 3B (H3F3B) are characteristically seen in GCTB and CBAs. We devised a simple assay to identify these mutations and evaluated its applicability for routine clinical diagnosis. One hundred twenty-four tissue specimens from 108 patients (43 GCTBs, 38 CBAs and 27 ABCs) were collected from the archives of the Calgary Laboratory Services/University of Calgary and Vanderbilt University Medical Center. Histology was reviewed by an expert orthopedic pathologist. A single base extension assay (SNaPshot) is used to interrogate each nucleotide in codons 34 and 36 of H3F3A and codon 36 of H3F3B. Final diagnoses were generated after re-reviewing cases and incorporating molecular findings. Of 43 GCTBs, 38 (88%) had an H3F3A G34W mutation; 35 of 38 CBAs (92%) had a K36M mutation in either H3F3B (N = 31; 82%) or H3F3A (N = 4; 11%); none of 27 ABCs had a tested mutation. Molecular findings changed the histomorphologic diagnosis in 5 cases (3 GCTB changed to ABC, and 2 ABC changed to GCTB). These findings support the diagnostic utility of mutational analysis for this differential diagnosis in certain challenging cases when clinicoradiologic and histomorphologic features are not definitive, particularly for distinguishing cellular ABC versus GCTB with secondary ABC., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Aneurysmal bone cyst (ABC) is a locally aggressive, expansile, typically multilocular cystic bone tumor. ABC was previously thought to be a non-neoplastic lesion; however, it is now considered to be neoplasm that features recurrent chromosomal translocations resulting in gene fusions between ubiquitin specific peptidase 6 (USP6) and multiple partners, including COL1A1, CDH11, TRAP150, ZNF90 and OMD. Using next generation sequencing (NGS), we uncovered two fusion partners of USP6 in two ABCs: platelet activating factor acetylhydrolase 1b regulatory subunit 1 (PAFAH1B1), which is known to contribute to tumorigenesis in lung cancer, and runt-related transcription factor 2 (RUNX2), which is known to regulate osteoblastic differentiation, osteosarcoma tumorigenesis and its metastasis. In our study, the PAFAH1B1-USP6 fusion consisted of the promoter of PAFAH1B1 fused to the 5'-untranslated region (5'-UTR) of USP6 and was discovered in a typical ABC. The RUNX2-USP6 fusion had the promoter and a short coding region of RUNX2 fused to the translation start codon of USP6 and was detected in an unusually aggressive ABC with an osteosarcoma-like soft tissue extension. Our findings not only expanded the repertoire of the partner genes of USP6 in ABC but also can serve as a reference for future studies to better understand the correlation between various gene fusions and the progression of ABC., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Primary aneurysmal bone cyst (ABC) is a neoplastic process due to recurrent translocations involving the USP6 gene. By fluorescence in situ hybridization, up to 69% of primary ABCs harbored USP6 translocations; no USP6 translocation was found in secondary ABC or giant cell tumor of bone (GCT). GCT can recur locally, metastasize to the lungs in some cases, and rarely undergo malignant transformation. Differentiating primary ABC from its mimics is important for treatment and prognosis. We evaluated USP6 fusion and expression in 13 cases of primary and 1 case of secondary ABC, and 9 cases of GCT using nucleic acid extracted from formalin-fixed, paraffin-embedded tissue and a next generation sequencing (NGS)-based assay. USP6 fusions including 7 novel fusions and USP6 transcripts were identified in all 13 primary ABCs. Nine cases with strong evidence of fusions showed high levels of USP6 transcripts by reverse transcription-PCR (RT-PCR). The remaining four had no detectable USP6 expression by a first-round of RT-PCR but the presence of USP6 transcripts was identified by a second-round, nested PCR. The major fusions were confirmed by RT-PCR followed by Sanger sequencing. No USP6 fusion or transcript was detected in any of the GCTs or the case of secondary ABC by NGS or by two rounds of PCR. All USP6 translocations resulted in fusion of the entire USP6 coding sequence with promoters of the fusion gene leading to upregulation of USP6 transcription, which is likely the underlying mechanism for ABC oncogenesis. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Aneurysmal bone cystic (ABC) lesions can be primary or secondary (to a trauma or a pre-existing benign or malignant tumour). Specific translocations of the USP6 gene are reported in about 70% of primary but never in secondary ABC lesions. We report two cases of ABC lesions in which imbalanced genomic aberrations were detected at initial presentation and showed complex clonal evolution. These demonstrative observations strengthen the guidelines regarding the diagnostic approach when an ABC is suggested by imaging. Biopsy is mandatory including genomic analysis. When a primary ABC is not clearly proven by the initial biopsy, an extensive curettage should be performed, with pathological examination of all removed tissue in order to exclude a secondary ABC. It also illustrates the added value of genomic analyses in the setting of an ABC lesion: complex clonal aberrations argues for a lesion secondary to a malignant proliferation whereas USP6 rearrangement allows the diagnosis of primary ABC.

The receptor-activator of nuclear kappaB ligand (RANKL) signaling pathway plays an important role in the regulation of bone growth and mediates the formation and activation of osteoclasts. Osteoclasts are involved in significant bone resorption and destruction. Denosumab is a fully human monoclonal antibody against RANKL that specifically inhibits osteoclast differentiation and bone resorption. It has been approved for use for multiple myeloma and bone metastases, as well as for giant cell tumor of bone. However, there is no previous report quantitatively, comparing RANKL expression in histologically varied bone tumors. Therefore, we analyzed the mRNA level of various bone tumors and investigated the possibility of these tumors as a new therapeutic target for denosumab. We examined RANKL mRNA expression in 135 clinical specimens of primary and metastatic bone tumors using real-time PCR. The relative quantification of mRNA expression levels was performed via normalization with RPMI8226, a human multiple myeloma cell line that is recognized to express RANKL. Of 135 cases, 64 were also evaluated for RANKL expression by using immunohistochemistry. Among all of the tumors investigated, RANKL expression and the RANKL/osteoprotegerin ratio were highest in giant cell tumor of bone. High RANKL mRNA expression was observed in cases of aneurysmal bone cyst, fibrous dysplasia, osteosarcoma, chondrosarcoma, and enchondroma, as compared to cases of multiple myeloma and bone lesions from metastatic carcinoma. RANKL-positive stromal cells were detected in six cases: five cases of GCTB and one case of fibrous dysplasia. The current study findings indicate that some primary bone tumors present new therapeutic targets for denosumab, particularly those tumors expressing RANKL and those involving bone resorption by osteoclasts.

We present the case of a 46-year-old woman with no significant past medical history who developed left mid-thigh pain and fullness. Imaging demonstrated a mineralized soft-tissue mass, which increased in size during a year of monitoring, but retained a circumscribed appearance. The mass was located in the medial soft tissues of the thigh, separate from the bone on imaging studies, and this finding was confirmed during excision. The mass showed gross and microscopic features of an aneurysmal bone cyst. This diagnosis was supported by cytogenetic analysis revealing a t(17;17)(p13;q21) translocation corresponding to the USP6 and COL1A1 loci. Soft-tissue aneurysmal bone cyst is a rare entity, with fewer than 25 reports in the literature. Limited cytogenetic information about these tumors is available. To our knowledge, the USP6 and COL1A1 rearrangement has only previously been described in a pediatric soft-tissue aneurysmal bone cyst. We also discuss the differential diagnosis of ossifying soft-tissue lesions.

Giant cell reparative granulomas (GCRGs) are lytic lesions that occur predominantly in the gnathic bones and occasionally in the small bones of the hands and feet. They are morphologically indistinguishable from, and are regarded as synonymous with, solid variant of aneurysmal bone cysts (ABC) in extragnathic sites. Identification of USP6 gene rearrangements in primary ABC has made possible investigating potential pathogenetic relationships with other morphologic mimics. USP6 gene alterations in giant cell-rich lesions (GCRG/ABC) of small bones of the hands and feet have not been previously studied. We investigated USP6 gene alterations in a group of 9 giant cell-rich lesions of the hands and feet and compared the findings with morphologically similar lesions including 8 gnathic GCRGs, 22 primary ABCs, 8 giant cell tumors of bone, and 2 brown tumors of hyperparathyroidism. Overall, there were 49 samples from 48 patients including 26 females and 22 males. Of the 9 lesions of the hands and feet, 8 (89%) showed USP6 gene rearrangements, whereas no abnormalities were identified in the 8 gnathic GCRGs, 2 brown tumors, or 8 giant cell tumors of bone. Of the 22 primary ABCs, 13 (59%) showed USP6 gene rearrangements. In conclusion, most GCRGs of the hands and feet represent true ABCs and should be classified as such. The terminology of GCRG should be limited to lesions from gnathic location. Fluorescence in situ hybridization for USP6 break-apart is a useful ancillary tool in the diagnosis of primary ABCs and distinguishing them from GCRGs and other morphologically similar lesions., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Alongside histomorphology and immunohistochemistry, molecular pathology is now established as one of the cornerstones in the tissue diagnosis of bone tumours. We describe the principal molecular pathological techniques employed, and each of the bone tumour entities where their identified characteristic molecular pathological changes can be detected to support and confirm the suspected histological diagnosis. Tumours discussed include fibrous dysplasia, classical and subtype osteosarcomas, central and surface cartilaginous tumours, Ewing's sarcoma, vascular tumours, aneurysmal bone cyst, chordoma, myoepithelioma, and angiomatoid fibrous histiocytoma. This is a rapidly evolving field with discoveries occurring every few months, and some of the newer entities (the Ewing's-like sarcomas), which are principally identified by their molecular pathology characteristics, are discussed., (© 2013 John Wiley & Sons Ltd.)

Aneurysmal bone cyst (ABC), once considered a reactive lesion, has been proven to be a neoplasia characterized by rearrangements of the USP6-gene. Aggressive local growth and recurrences are common and therapeutic options may be limited due to the vicinity of crucial structures. We describe a case of a locally aggressive, multinucleated giant cell-containing lesion of the forearm of a 21-year old woman, treated with denosumab for recurrent, surgically uncontrollable disease. Under the influence of this RANKL inhibitor, the tumor showed a marked reduction of the content of the osteoclastic giant cells and an extensive metaplastic osteoid production leading to the bony containment, mostly located intracortically in the proximal radius. The diagnosis of a periosteal ABC was confirmed by FISH demonstrating USP6 gene rearrangement on the initial biopsy. Function conserving surgery could be performed, enabling reconstruction of the affected bone. Inhibition of RANKL with denosumab may offer therapeutic option for patients not only with giant cell tumors but also with ABCs.

USP6 (also known as TRE17) is a ubiquitin-specific protease that was identified as an oncogene in transfection experiments with Ewing sarcoma DNA 2 decades ago. Until recently, little was known about USP6 function and mechanisms of oncogenic activation. The identification of USP6 fusion genes in aneurysmal bone cyst (ABC) and, more recently, in nodular fasciitis led to a better understanding of the pathogenesis of these lesions. Furthermore, the detection of USP6 genomic rearrangements or USP6 fusion genes may be used as a diagnostic tool for these lesions. In this review, we discuss the clinicopathologic features, molecular pathology, and pathogenesis of ABC and nodular fasciitis. We also discuss the possible line of differentiation of ABC and its relationship to nodular fasciitis and other lesions., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Aneurysmal bone cyst is a rapidly growing and locally aggressive lesion that commonly affects children and young adults. Initially regarded as a reactive process, primary aneurysmal bone cyst is now widely accepted as a neoplasm owing to recent findings of recurrent clonal chromosomal alterations, mostly t(16;17)(q22;p13). However, other infrequent chromosomal rearrangements have also been reported. Giant cell reparative granuloma, previously regarded as a nonneoplastic process and histologically indistinguishable from the solid variant of aneurysmal bone cyst, is frequently seen in the gnathic bones and the short tubular bones of the hands and feet. Here we present such a case of giant cell reparative granuloma (solid aneurysmal bone cyst) in the finger of a 63-year-old white man. Cytogenetic analysis revealed a novel alteration involving a reciprocal translocation between 6q and 13q, with a karyotype of 46,XY,t(6;13)(q15;q34),del(20)(q13.1)., (Copyright © 2012 Elsevier Inc. All rights reserved.)

USP6 rearrangement is the most common genetic abnormality in primary aneurysmal bone cyst, and SS18 rearrangement has not been previously described in any type of tumor where synovial sarcoma was excluded from the differential diagnosis. We report a case of solid aneurysmal bone cyst in which fluorescence in situ hybridization (FISH) analysis indicated rearrangements of both USP6 and SS18, but histologic features were consistent with aneurysmal bone cyst throughout the lesion. Reverse-transcription polymerase chain reaction (RT-PCR) for the SS18-SSX1 and SS18-SSX2 translocations, identity testing, and SS18 FISH were performed on cytogenetic monolayer cultures and formalin-fixed paraffin-embedded (FFPE) tissue. Genomic microarray, FISH, and immunohistochemistry were performed on follow-up studies of the FFPE specimen. The karyotype was 45,X,add(X)(p11.2),add(4)(q13),add(8)(p21),-13,add(17)(p11.2),add(18)(q11.2) in all 20 cells analyzed from monolayer cultures. The karyotype showed no cytogenetically visible alterations of chromosomal regions harboring known partners for USP6. Metaphase FISH with a commercial SS18 break-apart probe showed translocation of the 5' portion of the SS18 probe to the short arm of the derivative X, as is observed in synovial sarcoma. RT-PCR showed no evidence of a SS18-SSX fusion, and immunohistochemistry was negative for TLE1, EMA, and cytokeratin AE1/3 expression. FISH on FFPE sections with a custom break-apart probe flanking USP6 showed evidence for a USP6 rearrangement throughout the tumor (25-50%). FISH on FFPE sections with a commercial SS18 break-apart FISH probe showed more variable results (0-50% split signals). There was no evidence of a SS18-USP6 fusion by FISH or RT-PCR. A molecular inversion probe array revealed a deletion encompassing the entire SS18 gene and its promoter, as well as portions of the region targeted by the commercial SS18 FISH probe. In conclusion, results obtained from commercially available FISH probes may occasionally yield misleading results. In this case, the SS18 rearrangement by FISH resulted from a complex rearrangement of 18q11.2 with a deletion of the SS18 gene. The translocation partner for USP6 remains unknown in this case., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Aneurysmal bone cyst (ABC) is a pediatric osseous tumor characterized by extensive destruction of the surrounding bone. The molecular mechanisms underlying its pathogenesis are completely unknown. Recent work showed that translocation of the TRE17/USP6 locus occurs in over 60% of ABC cases resulting in TRE17 overexpression. Immature osteoblasts are presumed to be the cell type harboring translocation of TRE17 in at least a subset of ABCs. However, the effects of TRE17 overexpression on transformation and osteoblast function are unknown. TRE17 encodes a ubiquitin-specific protease (USP) and a TBC (TRE2-Bub2-Cdc16) domain that promotes activation of the Arf6 GTPase. Here we report that TRE17 potently inhibits the maturation of MC3T3 pre-osteoblasts in a USP-dependent and Arf6-independent manner. Notably, we find that TRE17 function is mediated through an autocrine mechanism. Transcriptome analysis of TRE17-expressing cells reveals dysregulation of several pathways with established roles in osteoblast maturation. In particular, signaling through the bone morphogenetic protein (BMP) pathway, a key regulator of osteogenesis, is profoundly altered. TRE17 simultaneously inhibits the expression of BMP-4 while augmenting the BMP antagonist, Gremlin-1. Osteoblastic maturation is restored in TRE17-expressing cells by the addition of exogenous BMP-4, thus establishing a functional role for BMP-4 during TRE17-induced transformation. Because bone homeostasis involves a precise balance between the activities of osteoblasts and osteoclasts, our studies raise the possibility that attenuated osteoblast maturation caused by TRE17 overexpression may contribute to the bone loss/destruction observed in ABC.

Aneurysmal bone cyst (ABC) is an aggressive, pediatric bone tumor characterized by extensive destruction of the surrounding bone. Although first described over 60 years ago, its molecular etiology remains poorly understood. Recent work revealed that ABCs harbor translocation of TRE17/USP6, leading to its transcriptional upregulation. TRE17 encodes a ubiquitin-specific protease (USP), and a TBC domain that mediates binding to the Arf6 GTPase. However, the mechanisms by which TRE17 overexpression contributes to tumor pathogenesis, and the role of its USP and TBC domains, are unknown. ABCs are characterized by osteolysis, inflammatory recruitment and extensive vascularization, the processes in which matrix proteases have a prominent role. This led us to explore whether TRE17 regulates the production of matrix metalloproteinases (MMPs). In this study we show that TRE17 is sufficient to induce expression of MMP-9 and MMP-10, in a manner requiring its USP activity, but not its ability to bind Arf6. TRE17 induces transcription of MMP-9 through activation of nuclear factor-kappaB (NF-kappaB), mediated in part by the GTPase RhoA and its effector kinase, ROCK. Furthermore, xenograft studies show that TRE17 induces formation of tumors that reproduce multiple features of ABC, including a high degree of vascularization, with an essential role for the USP domain. In sum, these studies reveal that TRE17 is sufficient to initiate tumorigenesis, identify MMPs as novel TRE17 effectors that likely contribute to ABC pathogenesis and define the underlying signaling mechanism of their induction.

Aneurysmal bone cysts (ABCs) are benign bone tumors consisting of blood-filled cavities lined by connective tissue septa. Recently, the hypothesis that ABCs are lesions reactive to local hemodynamics has been challenged after the discovery of specific recurrent chromosomal abnormalities. Multiple cases of malignant transformation of ABC into (osteo)sarcoma have been described, as well as a number of cases of telangiectatic osteosarcoma which had been misdiagnosed as ABC. We herewith document a case of a pelvic ABC metastatic to the lung, liver, and kidneys. Diagnosis was confirmed by the presence of a break in the USP6 gene, which is pathognomonic for ABC, in a pulmonary metastasis of our patient. Sarcomatous transformation as an explanation for this behavior was ruled out by demonstrating diploid DNA content in both the pulmonary lesion and the primary tumor.

Objective: USP6 rearrangements with several partner genes have been identified recently in primary but not in secondary aneurysmal bone cysts (ABCs). Several lesions show histologic features that may overlap with ABC, including myositis ossificans (MO), brown tumor, and cherubism. The objective of this study was to assess whether these lesions harbored USP6 rearrangements., Materials and Methods: Twelve patients with classic radiologic and histologic features of MO, 6 with brown tumors, and 5 with cherubism diagnosed at our institution were studied for the presence of USP6 rearrangements using fluorescence in situ hybridization with probes flanking the USP6 locus on chromosome 17p13. In addition, conventional cytogenetic analysis was performed in 2 patients with cherubism., Results: USP6 rearrangements were identified in 2 patients with radiologic and histologic features consistent with MO. None of the patients with brown tumor or cherubism demonstrated USP6 rearrangements. Cytogenetic analysis of the cherubism patients demonstrated normal karyotypes., Conclusion: These findings indicate that a subset of cases with apparent classic histologic and imaging features of MO are rather better classified as being soft-tissue ABC with clonal USP6 rearrangements. In contrast, no USP6 rearrangements were found in patients with cherubism or brown tumor, supporting the prevailing view that these lesions are distinct biologic entities.