Myositis ossificans-like soft tissue aneurysmal bone cyst: a clinical, radiological, and pathological study of seven cases with COL1A1-USP6 fusion and a novel ANGPTL2-USP6 fusion

Physiological roles and therapeutic implications of USP6

Ubiquitin-specific protease 6 (USP6) is a member of deubiquitinating enzyme family, recognized for its essential roles in physiological and pathological processes. USP6 is initially identified as a hominoid-specific enzyme residing on chromosome 17p13. USP6 is involved in regulating cellular functions, signaling pathways, protein degradation, intracellular trafficking, tumorigenesis and immune responses. USP6 is pivotal in signaling pathways, including NF-κB, JAK-STAT, and Wnt, which are fundamental for maintaining cellular homeostasis and mediating stress responses. Dysregulation of USP6 has been implicated in a spectrum of diseases, including bone tumors, breast and colorectal cancers, cranial fasciitis, and neurological disorders such as memory dysfunction. Furthermore, USP6 is involved in emerging therapeutic strategies highlighting its implications for drug development. A number of potential small molecule inhibitors are known to be responsible for suppression of USP6, such as Momelotinib (CYT387), FT385, USP30 Inh-1, -2 and -3, 2,6-Diaminopyridine-3,5-bis(thiocyanate) (PR-619) and so on. This review explores the emerging role of USP6 as a key regulator of cellular signaling pathways, its involvement in disease progression, its physiological functions, and the inhibitors that effectively suppress USP6 activity in detail. The comprehensive study provides insight to enhance our understanding of biological importance and therapeutic interventions of USP6 in drug development.

Detection of GRM1 gene rearrangements in chondromyxoid fibroma: a comparison of fluorescence in-situ hybridisation, RNA sequencing and immunohistochemical analysis

AIMS

Chondromyxoid fibroma (CMF) is a rare, benign bone tumour which arises primarily in young adults and is occasionally diagnostically challenging. Glutamate metabotropic receptor 1 (GRM1) gene encodes a metabotropic glutamate receptor and was recently shown to be up-regulated in chondromyxoid fibroma through gene fusion and promoter swapping. The aim of this study was to interrogate cases of CMF for the presence of GRM1 gene rearrangements, gene fusions and GRM1 protein overexpression.

METHODS AND RESULTS

Selected cases were subjected to testing by fluorescent in-situ hybridisation (FISH) with a GRM1 break-apart probe, a targeted RNA sequencing method and immunohistochemical study with an antibody to GRM1 protein. Two cases were subjected to whole transcriptomic sequencing. In 13 of 13 cases, GRM1 protein overexpression was detected by immunohistochemistry using the GRM1 antibody. Of the 12 cases successfully tested by FISH, nine of 12 showed GRM1 rearrangements by break-apart probe assay. Targeted RNA sequencing analysis did not detect gene fusions in any of the eight cases tested, but there was an increase in GRM1 mRNA expression in all eight cases. Two cases subjected to whole transcriptomic sequencing (WTS) showed elevated GRM1 expression and no gene fusions.

CONCLUSION

GRM1 gene rearrangements can be detected using FISH break-apart probes in approximately 75% of cases, and immunohistochemical detection of GRM1 protein over-expression is a sensitive diagnostic method. The gene fusion was not detected by targeted RNA sequencing, due most probably to the complexity of fusion mechanism, and is not yet a reliable method for confirming a diagnosis of CMF in the clinical setting.

ENG is a Biomarker of Prognosis and Angiogenesis in Liver Cancer, and Promotes the Differentiation of Tumor Cells into Vascular ECs

BACKGROUND

Liver cancer is a highly lethal malignancy with frequent recurrence, widespread metastasis, and low survival rates. The aim of this study was to explore the role of Endoglin (ENG) in liver cancer progression, as well as its impacts on angiogenesis, immune cell infiltration, and the therapeutic efficacy of sorafenib.

METHODS

A comprehensive evaluation was conducted using online databases Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA), 76 pairs of clinical specimens of tumor and adjacent non-tumor liver tissue, and tissue samples from 32 hepatocellular carcinoma (HCC) patients treated with sorafenib. ENG expression levels were evaluated using quantitative Reverse Transcription Polymerase Chain Reaction (qRT-PCR), Western blot, and immunohistochemical analysis. Cox regression analysis, Spearman rank correlation analysis, and survival analysis were used to assess the results. Functional experiments included Transwell migration assays and tube formation assays with Human Umbilical Vein Endothelial Cells (HUVECs).

RESULTS

Tumor cells exhibited retro-differentiation into endothelial-like cells, with a significant increase in ENG expression in these tumor-derived endothelial cells (TDECs). High expression of ENG was associated with more aggressive cancer characteristics and worse patient prognosis. Pathway enrichment and functional analyses identified ENG as a key regulator of immune responses and angiogenesis in liver cancer. Further studies confirmed that ENG increases the expression of Collagen type Iα1 (COL1A1), thereby promoting angiogenesis in liver cancer. Additionally, HCC patients with elevated ENG levels responded well to sorafenib treatment.

CONCLUSIONS

This study found that ENG is an important biomarker of prognosis in liver cancer. Moreover, ENG is associated with endothelial cell differentiation in liver cancer and plays a crucial role in formation of the tumor vasculature. The assessment of ENG expression could be a promising strategy to identify liver cancer patients who might benefit from targeted immunotherapies.

Soft tissue aneurysmal bone cyst presenting as an enlarging neck mass: Case report and review of the head and neck literature

Soft tissue aneurysmal bone cysts (STABCs) are rare neoplasms histopathologically identical to aneurysmal bone cysts. These benign lesions are characterized by thin, peripheral ossification and no skeletal continuity. STABC may be difficult to distinguish from myositis ossificans (MO) and malignant entities from imaging and fine needle aspiration, due to rarity and overlapping features. We present a case of a STABC occurring in the paraspinal cervical muscles. The imaging, histopathology, molecular analysis, and treatment are discussed. Four other published cases of STABC of the head and neck are reviewed.

Soft Tissue Aneurysmal Bone Cyst in the Sartorius Muscle of a 13-Year-Old Boy Mimicking Myositis Ossificans: Case Report

INTRODUCTION

A soft tissue aneurysmal bone cyst is an extremely rare tumor. The objective of the article is to present the clinical, radiological, and histopathological features of a very unusual neoplasm of soft tissues.

CASE REPORT

A 13-year-old male patient presented a painful, mobile, and rapidly growing mass on the posteromedial aspect of his left knee. Imaging studies revealed a mass that arose from the medial surface of the distal sartorius muscle, with extension to the subcutaneous fat tissue. It was a well-circumscribed solid tumor with a peripheral rim calcification on plain film, computerized tomography, and ultrasound (zonal phenomenon). On magnetic resonance imaging, a heterogenous mass on T1-weighted images (WI) and T2-WI was seen, with a peripheral hypointense rim in both sequences. An outstanding edema on T2-WI extending to the soft tissue and muscles of the medial compartment of the knee was detected. The mass was resected, and the "tumoral mimickers" histopathological and molecular (next-generation sequencing) diagnoses confirmed a soft tissue aneurysmal bone cyst. A follow-up showed that the patient was free of disease 12 months after surgery.

CONCLUSION

Soft tissue aneurysmal bone cyst is a rare tumor. Appropriate clinical and radiological correlation should be performed to differentiate it from other tumor mimickers.

Periosteal Fasciitis With Unusual Radiologic Features Harboring a Novel STAG1::USP6 Fusion Gene

Periosteal fasciitis is a subtype of nodular fasciitis originating from the periosteum. The diagnosis can be challenging and requires radiologic-pathologic correlation. Advances in molecular analysis confirmed that nodular fasciitis and its related lesions harbor a USP6 gene rearrangement with one of the several potential partners. Herein, we report a case of periosteal fasciitis with metaplastic bone formation detected incidentally during a radiologic survey for breast carcinoma. Radiologic examination revealed a 2.4 cm, heterogeneous, avidly enhancing lesion of the right femoral distal metaphysis concerning for low-grade periosteal chondrosarcoma. Histological examination of a core needle biopsy revealed a tumor composed of bland spindle cells with myofibroblastic and osteoblastic phenotypes admixed with immature bone and cartilaginous elements. Molecular analysis revealed a novel STAG1::USP6 fusion that helped arrive at the right diagnosis and further expands the molecular profile of USP6-associated neoplasms.

Unravelling the USP6 gene: an update

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.

Ubiquitin-specific proteases: Vital regulatory molecules in bone and bone-related diseases

Stabilization of bone structure and function involves multiple cell-to-cell and molecular interactions, in which the regulatory functions of post-translational modifications such as ubiquitination and deubiquitination shouldn't be underestimated. As the largest family of deubiquitinating enzymes, the ubiquitin-specific proteases (USPs) participate in the development of bone homeostasis and bone-related diseases through multiple classical osteogenic and osteolytic signaling pathways, such as BMP/TGF-β pathway, NF-κB/p65 pathway, EGFR-MAPK pathway and Wnt/β-catenin pathway. Meanwhile, USPs may also broadly regulate regulate hormone expression level, cell proliferation and differentiation, and may further influence bone homeostasis from gene fusion and nuclear translocation of transcription factors. The number of patients with bone-related diseases is currently enormous, making exploration of their pathogenesis and targeted therapy a hot topic. Pathological increases in the levels of inflammatory mediators such as IL-1β and TNF-α lead to inflammatory bone diseases such as osteoarthritis, rheumatoid arthritis and periodontitis. While impaired body metabolism greatly increases the probability of osteoporosis. Abnormal physiological activity of bone-associated cells results in a variety of bone tumors. The regulatory role of USPs in bone-related disease has received particular attention from academics in recent studies. In this review, we focuse on the roles and mechanisms of USPs in bone homeostasis and bone-related diseases, with the expectation of informing targeted therapies in the clinic.

Histopathogenesis of bone- and soft-tissue tumor spectrum with USP6 gene rearrangement: multiple partners involved in the tissue repair process

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.

Multimodality imaging features of USP6-associated neoplasms

Since the discovery of USP6 gene rearrangements in aneurysmal bone cysts nearly 20 years ago, we have come to recognize that there is a family of USP6-driven mesenchymal neoplasms with overlapping clinical, morphologic, and imaging features. This family of neoplasms now includes myositis ossificans, aneurysmal bone cyst, nodular fasciitis, fibroma of tendon sheath, fibro-osseous pseudotumor of digits, and their associated variants. While generally benign and in many cases self-limiting, these lesions may undergo rapid growth, and be confused with malignant bone and soft tissue lesions, both clinically and on imaging. The purpose of this article is to review the imaging characteristics of the spectrum of USP6-driven neoplasms, highlight key features that allow distinction from malignant bone or soft tissue lesions, and discuss the role of imaging and molecular analysis in diagnosis.

USP6-associated soft tissue tumors with bone metaplasia: Clinicopathologic and genetic analysis and the identification of novel USP6 fusion partners

Introduction

Among those tumors with consistent USP6 rearrangement, some arise from soft tissue and show bone metaplasia, including myositis ossificans (MO), fibro-osseous pseudotumor of digits (FOPD), soft tissue aneurysmal bone cyst (ST-ABC) and fasciitis ossificans (FO). These lesions are easily confused with malignancies because they show a rapid growth rate and brisk mitoses. Here, we aim to clarify the clinicopathologic and genetic characteristics of this entity and analyze the correlations among the different subtypes in one of the largest cohorts.

Materials and Methods

The clinicopathologic features of 73 cases of MO, FOPD, ST-ABC and FO diagnosed at West China Hospital, Sichuan University from January 2010 to December 2021 were retrospectively analyzed. Forty-three undecalcified samples were analyzed by systematic genetic studies, including fluorescence in situ hybridization (FISH), reverse transcription polymerase chain reaction (RT-PCR), Sanger sequencing and next-generation-based sequencing were performed.

Results

This series included 40 males and 33 females aged 2 to 80 years old (median: 31 years). FOPD occurred in extremal soft tissue, while lower extremities (38/58, 65.5%) were the most commonly involved lesions in the other three subgroups. Histologically, proliferative myofibroblasts/fibroblasts with varying degrees of osteoid tissue were present. Fluorescence in situ hybridization (FISH) results indicated that 22 cases (22/27, 81.5%) were positive for USP6 rearrangement, and 5 cases were negative. Among those cases with positive FISH results, 18 underwent reverse transcription-polymerase chain reaction (RT-PCR) detection that successfully detected common USP6 fusion types. Thirteen cases showed COL1A1::USP6 fusion, one showed MYH9::USP6 fusion, and 4 were negative for common fusion types. Next-generation-based sequencing technology was performed on two lesions with negative RT-PCR results and novel fusion partners SNHG3 and UBE2G1 were discovered.

Conclusions

Our findings revealed that COL1A1 is the most common fusion partner in this entity, unlike primary aneurysmal bone cysts and nodular fasciitis. Notably, we believed that FO may demonstrate more similar clinicopathologic and genetic manifestations with MO/FOPD and ST-ABC instead of nodular fasciitis for involving lower limbs most frequently and showing recurrent COL1A1::USP6 fusion. Additionally, this study also found two novel USP6 fusion partners, which further expanded our knowledge of this neoplastic spectrum.

Soft tissue aneurysmal bone cyst in thigh muscles: A case report

Aneurysmal bone cysts (ABCs) are benign lesions that are locally invasive. The prevalence of soft tissue ABCs is far lower than the intraosseous type. Here, we report a case of ABC in thigh muscles who presented with distal thigh pain.

Cranial Fasciitis in Children: Expanding the Spectrum of USP6-Associated Clonal Transient Neoplasms

Background: Cranial fasciitis (CF) is a benign (myo)fibroblastic proliferation of children. Typical presentation consists of a rapidly growing solitary mass on the temporal or parietal cranium in the first 2 years of age. CF is characterized by a rapid growth followed by a relative slowdown and even growth arrest. The finding of somatic USP6 gene rearrangements demonstrating clonality in CF together with its clinical behavior places it in the category of diseases recently termed "transient neoplasia."Methods: Histological, immunohistochemical, and molecular findings of 18 patients with CF were retrospectively studied.Results: The tumor typically presented as a painless rapidly enlarging mass in the temporal region. Sixty-six percent of the cases harbored USP6 gene rearrangement. Nine patients were treated with gross total resection (GTR) and 9 with subtotal tumor resection (STR). Two patients treated with GTR had recurrence. Five patients treated with STR had progression-free disease for at least 10 months after surgery and in four patients the tumor regressed spontaneously a median 16 months after surgery.Conclusions: In this largest series to date, we reported the clinicopathological, immunohistochemical, and molecular findings of 18 pediatric cases of CF with emphasis on the clinical growth pattern of these tumors.

Primary Aneurysmal Bone Cyst of Nasal Cavity and Sinuses in a Child: Case Report and Literature Review

INTRODUCTION

Aneurysmal bone cysts (ABCs) are a rare benign bone lesion, which are divided into primary and secondary categories, and occur mainly in the vertebra and the long tubular bones. Primary ABCs in the nasal cavity and the sinuses are rare.

CASE PRESENTATION

We reported on a one-year-old boy who suffered from progressive nasal obstruction and intermittent nosebleeds over a period of approximately 1 month. The patient had no history of trauma or surgery. Physical examination showed a red tumor in his right nasal cavity. A magnetic resonance imaging scan showed a multicystic lesion arising from the ethmoid sinus. The lesion was resected under a nasal endoscope without any complications. Histological evaluation confirmed that the lesion was an aneurysmal bone cyst. Because an osteoma was found during the surgery on the cyst, the lesion was considered secondary clinically. However, fluorescence in situ hybridization testing showed a rearrangement of the USP6 (ubiquitin-specific protease 6) oncogene on chromosome 17. No recurrence was observed after 1 year.

CONCLUSION

An ABC of the nasal cavity and sinuses in such a young child is very rare and needs to be further analyzed according to postoperative pathology and combined with a genetic examination to make a diagnosis. Endoscopic sinus surgery is an effective method of treatment for this kind of disease.

Aneurysmal bone cyst with an unusual clinical presentation and a novel VDR-USP6 fusion

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.

Current strategies for the treatment of solitary and aneurysmal bone cysts: A review of the literature

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SBCs can mostly be treated conservatively.

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In ABCs a biopsy is compulsory.

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ABCs can be treated by polidocanol instillations adequately.

This review of the literature aims to compare the etiology, the pathogenesis, the clinical diagnostics and the relevant treatment options of two different types of cystic bone lesions: the solitary bone cyst (SBC) and the aneurysmal bone cyst (ABC). Whereas the clinical symptoms and the radiographic appearance can be similar, the diagnostic pathway and the treatment options are clearly different.

The solitary bone cyst (SBC) represents a tumor-like bone lesion, occurring most frequently in the humerus and femur in children and adolescents. Pain caused by intercurrent pathological fractures is often the first symptom, and up to 87% of the cysts are associated with pathological fractures. In the majority of cases SBCs can be treated conservatively, especially in the upper extremity. However, if a fracture is completely dislocated, joint affecting, unstable or open, surgical treatment is necessary. Pain under weight bearing or regaining the ability to mobilize after fracture timely can necessitate surgical treatment in SBCs affecting the lower extremity. Spontaneous resolution can be seen in rare cases.

The aneurysmal bone cyst (ABC) is a benign, locally aggressive tumor that occurs in childhood and early adulthood. It usually affects the metaphysis of long bones but can also occur in the spine or the pelvis. ABC can be primary but also secondary to other bone pathologies. The diagnosis has to be confirmed by biopsy and histopathological examinations. With cytogenetic studies and the detection of specific translocations of the ubiquitin-specific protease (USP) 6 gene primary ABCs can be differentiated from secondary ABCs and other bone lesions. Among various modalities of treatment i.e. en bloc resection, intralesional curettage with adjuvants, embolization or the systemic application of denosumab, intralesional sclerotherapy using polidocanol is an effective and minimally invasive treatment of primary ABCs.

Primary Aneurysmal Bone Cyst and Its Recent Treatment Options: A Comparative Review of 74 Cases

(1) Background: An aneurysmal bone cyst (ABC) is a benign, locally aggressive tumor. Different treatment modalities are described in the literature i.e., en bloc resection, intralesional curettage and percutaneous sclerotherapy. (2) Methods: This single-center study is a review of 74 patients with primary ABCs who underwent a surgical treatment or polidocanol instillation. Cyst volume measurements using MRI and conventional radiographs are compared. (3) Results: The mean pre-interventional MRI-based cyst volume was 44.07 cm³ and the mean radiographic volume was 27.27 cm³. The recurrence rate after intralesional curettage with the need for further treatment was 38.2% (13/34). The instillation of polidocanol showed a significant reduction of the initial cyst volume (p < 0.001) but a persistent disease occurred in 29/32 cases (90.6%). In 10 of these 29 cases (34.5%) further treatment was necessary. After en bloc resection (eight cases) a local recurrence occurred in two cases (25%), in one case with the need for further treatment. (4) Conclusions: MRI scans are superior to biplanar radiographs in the examination of ABCs. Sequential percutaneous instillations of polidocanol are equally effective in the therapy of primary ABCs compared to intralesional curettage. However, several instillations have to be expected. In a considerable number of cases, a conversion to intralesional curettage or en bloc resection may be necessary.

Ubiquitin-specific Peptidase 6 (USP6)-associated Fibroblastic/Myofibroblastic Tumors: Evolving Concepts

Ubiquitin-specific peptidase 6 (USP6) is a hominoid-specific gene residing on chromosome 17p13 and serves as a deubiquitinating enzyme with a diverse set of functions including intracellular trafficking, inflammatory signaling, cell transformation and protein turnover. USP6 rearrangements were first identified in aneurysmal bone cysts, resulting in promoter swapping and over-expression of wild type USP6. Several morphologically overlapping fibroblastic/myofibroblastic tumors are known to harbor USP6 rearrangements, including nodular fasciitis, cellular fibroma of tendon sheath, myositis ossificans and fibro-osseous pseudotumor of digits. Over the past few years, fusions involving the USP6 gene and various partner genes have been described in these neoplasms. The current World Health Organization Classification of Tumors of Soft Tissue suggests that USP6-rearranged lesions are typically benign and usually self-limited in their growth. This review provides an updated overview of the clinical, histological and molecular genetic features of USP6-associated fibroblastic/myofibroblastic tumors and discusses how these lesions should be best classified.

Clinicopathological and molecular characterisation of USP6-rearranged soft tissue neoplasms: the evidence of genetic relatedness indicates an expanding family with variable bone-forming capacity

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.

Myositis ossificans-a rare tumor of the chest wall

Myositis ossificans (MO) is the abnormal formation of benign heterotopic bone tissue in soft tissues or muscles, mostly in sites of trauma. Though it has been described in most parts of the body, less than a dozen cases involving the chest wall have been reported. It is known to resolve spontaneously and various medical treatments have been suggested to hasten its resolution. Large tumors, suspicion of malignancy, and presence of symptoms are indications for surgical intervention. The differential diagnoses include sarcomas, infections, callous, calcified hematomas, and cysts. We present the clinical, radiological, and pathological images of a post traumatic MO of the chest wall, arising from under the medial third of the clavicle and growing into the deeper surface of the pectoralis major muscle. The patient is doing well eight months after the excision of the same.

USP6-Associated Neoplasms: A Rapidly Expanding Family of Lesions

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).