Intramuscular Hybrid Nerve Sheath Tumor of the Thigh: Case Report and Literature Review.

BACKGROUND/AIM: Hybrid nerve sheath tumor (HNST) is a benign peripheral nerve sheath tumor with combined features of more than one histological type, such as schwannoma, neurofibroma, and perineurioma. It remains under-recognized in routine clinical practice. Herein, we describe an unusual case of intramuscular HNST of the thigh. CASE REPORT: The patient was a 41-year-old man with no history of trauma who presented with a 3-month history of a palpable mass in the right thigh. Physical examination revealed a 4-cm, elastic hard, mobile, nontender mass. Magnetic resonance imaging exhibited a well-circumscribed intramuscular mass with low-to-intermediate signal intensity on T1-weighted sequences and higher signal intensity peripherally and lower signal intensity centrally, representing a target sign, on T2-weighted sequences. Complete surgical excision of the tumor was carried out. Microscopically, the tumor showed dual histological components of both schwannoma and neurofibroma. Immunohistochemically, the schwannomatous component was strongly and diffusely positive for S-100 protein and negative for CD34, while the neurofibromatous component contained CD34-positive fibroblasts and S-100 protein-positive Schwann cells. Epithelial membrane antigen was negative for both components. These findings were consistent with a diagnosis of HNST (hybrid schwannoma/neurofibroma). The patient had no evidence of local recurrence and no neurological deficit at the final follow-up. CONCLUSION: Although extremely rare, HNST should be included in the extended differential diagnosis of a well-circumscribed, intramuscular soft-tissue mass in the extremities, particularly in young and early middle-aged adults.

Recent Advances in the Diagnosis, Pathogenesis, and Management of Myxoinflammatory Fibroblastic Sarcoma.

Myxoinflammatory fibroblastic sarcoma (MIFS) is an infiltrative, locally aggressive fibroblastic neoplasm of intermediate malignancy that typically arises in the distal extremities of middle-aged adults. It can histologically be confused with a number of benign and malignant conditions. Recently, high-grade examples of MIFS have been described. Immunohistochemistry plays a very limited role in the diagnosis of MIFS. Several genetic alterations have been identified in MIFS, including a t(1;10)(p22;q24) translocation with TGFBR3 and/or OGA rearrangements, BRAF rearrangement, and VGLL3 amplification. Although it appears that VGLL3 amplification is the most consistent alteration, the molecular pathogenesis of MIFS remains poorly understood. A wide resection is considered the standard treatment for MIFS. Radiotherapy may be a viable option in cases with inadequate surgical margins or cases where surgery is likely to cause significant functional impairment. The systemic treatment options for advanced or metastatic disease are very limited. This review provides an updated overview of the clinicoradiological features, pathogenesis, histopathology, and treatment of MIFS.

Giant Cell Tumor of the Acromion: Case Report and Literature Review.

BACKGROUND/AIM: Giant cell tumor of bone (GCTB) is a locally aggressive neoplasm that typically occurs in the ends (epiphyses) of long bones of young adults. Flat bones are uncommon sites of involvement. Herein, we describe an unusual case of pathologically proven GCT of the acromion. CASE REPORT: The patient was a 39-year-old woman with no history of trauma who presented with a 3-month history of right posterior shoulder pain. Physical examination revealed mild swelling and tenderness in the posterior aspect of the right shoulder. Plain radiograph showed a purely lytic lesion, suggestive of a bone tumor. Computed tomography demonstrated an intraosseous lytic lesion with associated cortical thinning and lack of periosteal reaction. On magnetic resonance imaging, the lesion exhibited slightly higher signal intensity compared to skeletal muscle on T1-weighted sequences and heterogeneous high signal intensity on T2-weighted sequences. Strong enhancement was observed following gadolinium administration. The lesion was treated by extensive curettage with adjuvant therapy comprising ethanol and the remaining cavity was filled with polymethylmethacrylate bone cement. Histologically, the lesion was composed of round or spindle-shaped mononuclear cells admixed with numerous osteoclast-like giant cells. Immunohistochemically, the mononuclear neoplastic cells were diffusely positive for H3.3 G34W. The patient was asymptomatic and there was no evidence of local recurrence or distant metastasis 5 months after surgery. CONCLUSION: Although rare, acromial GCTB should be considered in the differential diagnosis of posterior shoulder pain, especially in young and early middle-aged adults.

Biology and Management of High-Grade Myxofibrosarcoma: State of the Art and Future Perspectives.

Myxofibrosarcoma (MFS) is one of the most common adult soft tissue sarcomas, typically arising in the extremities. Histologically, MFS is classified into three grades: low, intermediate, and high. Histological grades correlate with distant metastases and tumor-associated mortality. The diagnosis of MFS is challenging due to a lack of well-characterized immunohistochemical markers. High-grade MFS displays highly complex karyotypes with multiple copy number alterations. Recent integrated genomic studies have shown the predominance of somatic copy number aberrations. However, the molecular pathogenesis of high-grade MFS remains poorly understood. The standard treatment for localized MFS is surgical resection. The systemic treatment options for advanced disease are limited. This review provides an updated overview of the clinical and imaging features, pathogenesis, histopathology, and treatment of high-grade MFS.

Biology and Management of Deep-seated Atypical Lipomatous Tumor of the Extremities.

Adipocytic neoplasms are frequently encountered in clinical practice. Atypical lipomatous tumor (ALT) is a locally aggressive but non-metastasizing adipocytic neoplasm that primarily occurs in the proximal extremities of middle-aged to older adults. Histologically, ALT is divided into adipocytic (lipoma-like), sclerosing and inflammatory subtypes. The sclerosing subtype is an unfavorable prognostic factor for local recurrence. ALT is characterized by supernumerary ring and/or giant rod chromosomes. These rings and giant markers invariably contain amplified sequences originating from the long arm of chromosome 12, including the MDM2 proto-oncogene (MDM2) and cyclin-dependent kinase 4 (CDK4) gene. MDM2 and/or CDK4 nuclear immunopositivity is present in most cases. Confidently differentiating deep-seated ALT from deep-seated ordinary lipoma is often difficult on imaging. Moreover, the sclerosing subtype may mimic a higher grade liposarcoma. Detection of MDM2 amplification by fluorescence in situ hybridization would be helpful diagnostically for ALT in more difficult cases. The standard treatment for deep-seated ALT is surgery. Although there is no consensus on the best surgical approach for deep-seated ALT of the extremities, the use of marginal resection is acceptable to preserve musculoskeletal function. This review provides an overview of the current knowledge on the clinical and imaging characteristics, pathogenesis, histopathology, and management of deep-seated ALT of the extremities.

Spindle Cell Lipoma and Pleomorphic Lipoma: An Update and Review.

Spindle cell lipoma (SCL) is a benign adipocytic tumor that primarily occurs in the subcutis of the posterior neck, upper back, and shoulder, particularly of middle-aged males. SCL and pleomorphic lipoma (PL) represent a morphological spectrum of one disease process. The lesion typically presents as a relatively small (<5 cm), mobile, slow-growing, painless mass. Magnetic resonance imaging reveals the lesion to be a well-defined subcutaneous mass with a mixture of adipose and non-adipose components. Intense enhancement of the non-adipose component is seen after contrast administration. Histologically, SCL is composed of variable distributions of mature adipocytes, bland spindle cells and ropey collagen bundles and PL also contains pleomorphic and multinucleated floret-like giant cells. By immunohistochemistry, the spindle and pleomorphic/floret-like giant cells of SCL/PL are diffusely positive for CD34 and show loss of nuclear RB transcriptional corepressor 1 (RB1) expression. Recent cytogenetic and molecular genetic studies have shown heterozygous deletions of 13q14, including the RB1 gene. SCL/PL can be successfully treated with simple excision, with a very low recurrence rate. Knowledge of these peculiar tumors is important because it can mimic a variety of benign and malignant soft-tissue tumors. This review provides an updated overview of the clinical, radiological, histopathological, cytogenetic, and molecular genetic features of SCL/PL.

An Update on Clinicopathological, Imaging, and Genetic Features of Angioleiomyoma.

Angioleiomyoma is a benign, pericytic (perivascular) neoplasm that primarily occurs in the subcutis or dermis of the extremities. The lesion typically presents as a small, firm, slow-growing, painful nodule. Magnetic resonance imaging reveals the lesion to be a well-defined, round to oval mass with signal intensity similar to or slightly hyperintense to that of skeletal muscle on T1-weightwed sequences. A dark reticular sign on T2-weighted sequences appears to be a characteristic feature of angioleiomyoma. Prominent enhancement is usually seen after intravenous contrast. Histologically, the lesion consists of well-differentiated smooth muscle cells with many vascular channels. Based on vascular morphologies, angioleiomyoma is classified into three subtypes: solid, venous, and cavernous. By immunohistochemistry, angioleiomyoma is diffusely positive for smooth muscle actin and calponin and variably for h-caldesmon and desmin. Conventional cytogenetic studies have demonstrated relatively simple karyotypes characterized by one or few structural rearrangements or numerical aberrations. In addition, metaphase comparative genomic hybridization analyses have revealed recurrent loss of 22q and gain of Xq. Angioleiomyoma can be successfully treated with simple excision, with a very low recurrence rate. Knowledge of this peculiar neoplasm is important because it can mimic a variety of benign and malignant soft-tissue tumors. This review provides an updated overview of the clinical, radiological, histopathological, cytogenetic, and molecular genetic features of angioleiomyoma.

Identification and characterization of sperm motility-initiating substance-2 gene in internally fertilizing Cynops species.

Sperm motility-initiating substance (SMIS) is an oviductal protein critical for internal fertilization in urodeles. It contributes to the establishment of various reproductive modes in amphibians and is thus a unique research model for the gene evolution of gamete-recognizing ligands that have diversified among animal species. In this study, a paralogous SMIS gene, smis2, was identified via the RNA sequencing of the oviduct of the newt, Cynops pyrrhogaster. The base sequence of the smis2 gene was homologous (˃90%) to that of the original smis gene (smis1), and deduced amino acid sequences of both genes conserved six cysteine residues essential for the cysteine knot motif. Furthermore, smis2 complementary DNA was identified in the oviduct of Cynops ensicauda, and the base substitution patterns also suggested that the smis gene was duplicated in the Salamandridae. Nonsynonymous/synonymous substitution ratios of smis1 and smis2 genes were 0.79 and 2.6, respectively, suggesting that smis2 gene evolution was independently driven by positive selection. Amino acid substitutions were concentrated in the cysteine knot motif of SMIS2. The smis2 gene was expressed in some organs in addition to the oviduct; in contrast, SMIS1 was only expressed in the oviduct. The SMIS2 protein was suggested to be produced and secreted at least in the oviduct and redundantly act in sperm. These results suggest that smis1 plays the original role in the oviduct, whereas smis2 may undergo neofunctionalization, which rarely occurs in gene evolution.

Superficial Angiomyxoma of the Wrist: Case Report and Literature Review.

BACKGROUND/AIM: Superficial angiomyxoma (SAM) is a rare benign soft-tissue tumor that usually occurs in the trunk, head and neck, and lower extremity of middle-aged adults. Herein, we describe an unusual case of SAM of the wrist, which was initially diagnosed as a ganglion cyst on imaging. CASE REPORT: The patient was a 71-year-old man with no history of trauma who presented with a 2-year history of a palpable mass in the left wrist. Physical examination revealed a 2.5-cm, elastic hard, mobile, nontender mass. Magnetic resonance imaging revealed a well-defined mass with iso-signal intensity relative to skeletal muscle on T1-weighted sequences and very high signal intensity on T2-weighted fat-suppressed sequences. Subtle internal enhancement was seen following gadolinium administration. Complete excision was performed under general anesthesia with tourniquet control. Histologically, the lesion was composed of bland spindle to stellate-shaped cells in an abundant myxoid stroma. Immunohistochemically, the lesional cells were positive for CD34 but negative for S-100 protein, smooth-muscle actin, desmin, epithelial membrane antigen and pancytokeratin. These findings were consistent with a diagnosis of SAM. There was no clinical evidence of recurrence during a follow-up period of 3 months. CONCLUSION: Although extremely rare, SAM should be considered in the differential diagnosis of a cyst-like solid lesion near small joints.

GLUT-1 expression is helpful to distinguish myxofibrosarcoma from nodular fasciitis.

Myxofibrosarcoma (MFS) is a fibroblastic/myofibroblastic neoplasm with a variably myxoid stroma. Histologically, MFS shows a wide spectrum of cellularity, pleomorphism and proliferative activity. Because of its variable morphology and lack of discriminatory markers, MFS can be difficult to distinguish from some benign soft-tissue tumors, especially nodular fasciitis (NF). Glucose transporter 1 (GLUT-1) is expressed in a variety of malignant mesenchymal tumors. In the current study, we evaluated GLUT-1 expression to determine its value in distinguishing MFS from NF. Tissue specimens from 14 MFS cases and 16 NF cases were sectioned and stained for GLUT-1 using immunohistochemistry. The percentage of GLUT-1-positive cells was scored as follows: 0 (no staining), 1+ (1-19%), 2+ (20-50%) and 3+ (>50%). Samples with a score of 1+ were defined as GLUT1-expressing samples. GLUT-1 expression was seen in all 14 MFS cases, whereas only 6 NF cases (37.5%) were positive for GLUT-1 and were scored 1+. Notably, 2-3+ GLUT-1 expression was found in 86% of MFS cases and 0% of NF cases. Our results indicate that GLUT-1 is a highly sensitive immunohistochemical marker for MFS and may be useful for the differential diagnosis of MFS and NF.

Arthroscopic Excision of Intra-articular AHRR-NCOA2- positive Angiofibroma of Soft Tissue of the Knee: A Case Report.

BACKGROUND/AIM: Angiofibroma of soft tissue (AFST) is a rare benign soft-tissue tumor that most frequently occurs in the lower extremities. It has a characteristic genetic feature with a balanced chromosomal translocation t(5;8)(p15;q13), resulting in a fusion of aryl hydrocarbon receptor repressor (AHRR) and nuclear receptor coactivator 2 (NCOA2). CASE REPORT: A 55-year-old woman presented with a 2-year history of left knee pain and recently noticed the development of a palpable mass. Magnetic resonance imaging exhibited a well-defined intra-articular mass with iso-signal intensity relative to skeletal muscle on T1-weighted sequences, heterogeneous high signal intensity on T2-weighted sequences and avid, diffuse enhancement on contrast-enhanced fat-suppressed T1-weighted sequences. After an ultrasound-guided core needle biopsy, the lesion was successfully treated by arthroscopically-assisted complete excision. Histologically, the tumor was composed of uniform bland spindle cells in a myxoid to collagenous stroma with a prominent vascular network. Immunohistochemically, the spindle cells were diffusely positive for CD163 and CD68 and focally positive for estrogen receptor. Moreover, AHRR-NCOA2 fusion gene was detected by reverse transcription-polymerase chain reaction. There has been no clinical evidence of local recurrence at 1-year follow-up. CONCLUSION: This is the first report of the detection of an AHRR-NCOA2 gene fusion associated with intra-articular AFST. AFST should be included in the extended differential diagnosis of an intra-articular soft-tissue mass, particularly if the mass is vascular.

t(1;2)-Positive Localized Tenosynovial Giant Cell Tumor With Bone Invasion.

BACKGROUND: Localized tenosynovial giant cell tumor (LTGCT) is one of the most common benign soft-tissue tumors of the foot. Although pressure erosion in the adjacent bone may be seen, intraosseous invasion of LTGCT is extremely rare. Recent molecular studies have identified the presence of pathognomonic translocation involving the colony stimulating factor 1 (CSF1) gene at 1p13. CASE REPORT: We present an unusual case of LTGCT mimicking a malignant tumor on imaging. The patient was a 16-year-old woman with no history of trauma who presented with a 2-year history of a slow-growing, painless mass in the left fourth toe. Physical examination revealed a 2-cm, elastic hard, immobile, nontender mass. Plain radiograph showed a lytic lesion with a partially sclerotic rim in the proximal phalanx of the fourth toe. Computed tomography demonstrated an expansile lesion with plantar cortical destruction. Magnetic resonance imaging revealed a nodular mass with intermediate signal intensity on T1-weighted sequences and heterogeneous high signal intensity on T2-weighted sequences. The mass had intense contrast enhancement. Complete excision of the mass was performed, and the bone defect was repaired with calcium phosphate cement. Cytogenetic analysis revealed a t(1;2)(p13;q37) translocation as the sole anomaly. Fluorescence in situ hybridization demonstrated the presence of CSF1 rearrangements. CONCLUSION: Although extremely rare, LTGCT should be considered in the differential diagnosis of an intraosseous lesion near small joints, especially when seen in the toe.

Prognostic Factors of Pulmonary Metastasectomy for Soft Tissue Sarcomas Arising in the Trunk Wall and Extremities.

Although there is no evidence from prospective randomized controlled trials to support this practice, pulmonary metastases of sarcomas are often treated surgically if they are resectable. The purpose of this retrospective study was to evaluate the prognostic factors and outcome of pulmonary metastasectomy (PM) for soft tissue sarcomas (STSs) arising in the trunk wall and extremities in 66 consecutive patients. Prognostic factors associated with disease-specific survival after PM were evaluated using univariate and multivariate analyses. The patients included 38 men and 28 women, with a median age of 49 years. The median disease-specific survival after PM was 48 months, and the 5-year survival rate was 45%. No major perioperative complications occurred. Disease-free interval (<12 months), size of largest lung lesion (≥20 mm), and non-curative resection were independent prognostic factors in multivariate analysis. PM was effective in selected patients with pulmonary metastases from STSs arising in the trunk wall and extremities. Disease-free interval, maximum size of metastases, and resectability were identified as prognostic factors.

Are there differences in arthroscopic and histological features between traumatic and degenerative rotator cuff tears in elderly patients? A prospective dual-center analysis.

BACKGROUND: Discriminating traumatic rotator cuff tears (RCTs) from degenerative RCTs is sometimes difficult in elderly patients because the prevalence of asymptomatic RCTs increases with age. Little intraoperative information is available on the characteristics of traumatic and degenerative RCTs in elderly patients. The purpose of this study was to compare the arthroscopic findings and histological changes of the coracoacromial ligament (CAL) between traumatic and degenerative RCTs in elderly patients. METHODS: Forty-two shoulders of 42 patients aged ≥ 65 years underwent arthroscopic rotator cuff repair. Nineteen patients had traumatic full-thickness RCTs (Group T), and 23 had degenerative full-thickness RCTs (Group D). The quality of the rotator cuff tissue and the condition of the long head of the biceps were examined. The grade of CAL was evaluated both arthroscopically and histologically. The stiffness of the musculotendinous unit was calculated by measuring the force and displacement using a tensiometer. The arthroscopic and histological findings of the two groups were compared. RESULTS: Although the mean tendon displacement was comparable, the stiffness was different between Group T and Group D (0.56 ± 0.31 and 1.09 ± 0.67 N/mm, respectively; p < 0.001). Both arthroscopic and histological analysis of the CAL showed that the degenerative changes in the CAL were milder in Group T than in Group D (p < 0.001 and p < 0.001, respectively). There was a moderate positive correlation between the arthroscopic findings of CAL degeneration and the histopathological changes in this ligament (r = 0.47, p = 0.002). CONCLUSIONS: Traumatic RCTs were characterized by preserved elasticity of the musculotendinous unit and milder CAL degeneration compared with degenerative RCTs even in elderly patients.

Angiofibroma of soft tissue: Current status of pathology and genetics.

Angiofibroma of soft tissue (AFST) is a new soft tissue tumor entity described in the 2020 World Health Organization Classification of Soft Tissue and Bone Tumors. It most often arises in the lower extremities of middle-aged adults and pursues a benign clinical course with a low rate of non-destructive local recurrence. Histologically, the lesion consists of uniform bland spindle cells in a fibromyxoid stroma with a prominent vascular network. The vascular component forms a complex arrangement of small, thin-walled branching blood vessels. By immunohistochemistry, AFST is variably positive for epithelial membrane antigen, desmin, smooth muscle actin, CD34, CD68, CD163 and estrogen receptor. The exact etiology of AFST remains unknown, but it appears genetically distinct, with a balanced t(5;8)(p15;q13) translocation resulting in a fusion of aryl hydrocarbon receptor repressor (AHRR) and nuclear receptor coactivator 2 (NCOA2). Knowledge of this recently described entity is important because it can mimic a variety of intermediate and malignant soft tissue tumors, including solitary fibrous tumor, low-grade fibromyxoid sarcoma, myxoid liposarcoma and low-grade myxofibrosarcoma. We review AFST, with an emphasis on the diagnostic spectrum, recent molecular genetic features and the differential diagnosis.

Histopathologic evaluation of bone marrow lesions in early stage subchondral insufficiency fracture of the medial femoral condyle.

Subchondral insufficiency fracture (SIF) of the medial femoral condyle has been proposed to be a primary event in so-called 'spontaneous osteonecrosis of the knee'. SIF is also known to be associated with bone marrow lesions (BML), but the detailed histopathology of the BML has not been fully clarified. We thus investigated the pathophysiology of BML based on MRI and histology in the 4 consecutive patients diagnosed with SIF, whose onset was within 4 months. In all cases, BMLs were enhanced on T1 Gd-enhanced MRI. Histologically, BMLs comprised serous exudate, fibrous tissue, and vascular-rich granulation tissue in the marrow space. In addition, a lower signal intensity line was observed within the BML in all cases on T1 MRI. Histologically, this line showed thickened bone trabeculae accompanied by fibrovascular tissue in two cases, while the other two cases showed formation of woven bone trabeculae around the original fractured bone trabeculae indicating the presence of another fracture in the bone marrow space. In summary, BML in SIF was considered to be a secondary phenomenon resulting from a subchondral fracture.

Biology and Management of Dedifferentiated Liposarcoma: State of the Art and Perspectives.

Dedifferentiated liposarcoma (DDL) is defined as the transition from well-differentiated liposarcoma (WDL)/atypical lipomatous tumor (ALT) to non-lipogenic sarcoma, which arises mostly in the retroperitoneum and deep soft tissue of proximal extremities. It is characterized by a supernumerary ring and giant marker chromosomes, both of which contain amplified sequences of 12q13-15 including murinedouble minute 2 (MDM2) and cyclin-dependent kinase 4 (CDK4) cell cycle oncogenes. Detection of MDM2 (and/or CDK4) amplification serves to distinguish DDL from other undifferentiated sarcomas. Recently, CTDSP1/2-DNM3OS fusion genes have been identified in a subset of DDL. However, the genetic events associated with dedifferentiation of WDL/ALT remain to be clarified. The standard treatment for localized DDL is surgery, with or without radiotherapy. In advanced disease, the standard first-line therapy is an anthracycline-based regimen, with either single-agent anthracycline or anthracycline in combination with the alkylating agent ifosfamide. Unfortunately, this regimen has not necessarily led to a satisfactory clinical outcome. Recent advances in the understanding of the pathogenesis of DDL may allow for the development of more-effective innovative therapeutic strategies. This review provides an overview of the current knowledge on the clinical presentation, pathogenesis, histopathology and treatment of DDL.

Current Update on the Diagnosis, Management and Pathogenesis of Elastofibroma Dorsi.

Elastofibroma dorsi is an uncommon benign fibroblastic pseudotumor that typically occurs in the subscapular region of middle-aged or older individuals. The pathogenesis is still unclear and a matter of debate. Magnetic resonance imaging can be used as a first-line investigation of the lesion and reveals a lenticular soft-tissue mass with a signal intensity similar to that of skeletal muscle interlaced with strands of fat. Biopsy is not necessary if all pathognomonic criteria are present. A conservative "wait and see" attitude is reasonable and immediate surgery is no more the standard treatment of elastofibroma dorsi. This review provides an updated overview of the diagnosis, management and pathogenesis of elastofibroma dorsi. We also discuss recent advances in our understanding of genomic alterations in elastofibroma dorsi.

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.

An Update on Clinicopathological, Imaging and Genetic Features of Desmoplastic Fibroblastoma (Collagenous Fibroma).

Desmoplastic fibroblastoma (also known as collagenous fibroma) is an uncommon benign fibroblastic/myofibroblastic neoplasm that primarily arises in the subcutaneous tissue of upper extremity. Magnetic resonance imaging reveals a well-defined mass in intimate association with dense connective tissue and prominent low signal intensity on all pulse sequences. Peripheral and septal enhancement is usually seen after intravenous contrast. Histologically, the lesion is paucicellular and consists of spindle to stellate-shaped cells embedded in a collagenous or myxocollagenous stroma with low vascularity. Diffuse and strong nuclear immunoreactivity for FOS-like antigen 1 seems to be characteristic of desmoplastic fibroblastoma. Cytogenetic studies have demonstrated the presence of 11q12 rearrangements and an identical t(2;11)(q31;q12) translocation. This review provides an updated overview of the clinical, radiological, histological, cytogenetic and molecular genetic features of desmoplastic fibroblastoma and discusses the relationship to fibroma of tendon sheath.