A concise review of angiofibroma of soft tissue: A rare newly described entity that can be encountered by dermatopathologists

CYP1A1 immunohistochemistry is highly specific for angiofibroma of soft tissue among morphological mimics

AIMS

Angiofibroma of soft tissue (AFST) is a benign, morphologically distinctive tumour type that harbours recurrent AHRR::NCOA2 fusions in 60-70% of cases and shows a non-specific immunophenotype, expressing EMA in roughly half of cases. The AHRR::NCOA2 fusion results in increased expression of cytochrome P450 1A1 (CYP1A1); a recent study demonstrated CYP1A1 immunohistochemistry (IHC) to be moderately sensitive and highly specific for AFST.

METHODS AND RESULTS

In this study, we sought to validate these findings in a larger independent cohort of 30 AFST, as well as 215 morphological mimics, including 30 solitary fibrous tumours, 29 myxoid liposarcomas, 28 low-to-intermediate grade myxofibrosarcomas (MFS), 20 atypical spindle cell lipomatous tumours (ASCLT), 20 cellular angiofibromas, 10 cases each of spindle cell lipoma, neurofibroma, malignant peripheral nerve sheath tumour, superficial angiomyxoma, cellular myxoma, soft tissue perineurioma and deep fibrous histiocytoma, and nine cases each of low-grade fibromyxoid sarcoma and mammary-type myofibroblastoma. We found CYP1A1 IHC to be 70% sensitive for AFST, with granular cytoplasmic staining in 21 of 30 tumours, and 98% specific, with staining in only five morphological mimics: two deep fibrous histiocytomas, one MFS, one cellular angiofibroma and one ASCLT.

CONCLUSIONS

These findings confirm that CYP1A1 is 70% sensitive, consistent with the prevalence of AHRR::NCOA2 fusions that up-regulate this protein, and that it is highly specific among morphological mimics.

Clinicopathologic and genetic characterization of angiofibroma of soft tissue: a study of 12 cases including two cases with AHRR::NCOA3 gene fusion

AIMS

Angiofibroma of soft tissue (AFST) is a benign tumour characterised by prominent arborizing blood vessels throughout the lesion. Approximately two-thirds of AFST cases were reported to have AHRR::NCOA2 fusion, and only two cases have been reported to have other gene fusions: GTF2I::NCOA2 or GAB1::ABL1. Although AFST is included in fibroblastic and myofibroblastic tumours in the World Health Organization's 2020 classification, histiocytic markers, especially CD163, have been reported to be positive in almost all examined cases, and it still remains the possibility of a fibrohistiocytic nature of the tumour. Therefore, we aimed to clarify the genetic and pathological spectrum of AFST and identify whether histiocytic marker-positive cells were true neoplastic cells.

METHODS AND RESULTS

We evaluated 12 AFST cases, which included 10 cases with AHRR::NCOA2 and two with AHRR::NCOA3 fusions. Pathologically, nuclear palisading, which has not been reported in AFST, was detected in two cases. Furthermore, one tumour resected by additional wide resection revealed severe infiltrative growth. Immunohistochemical analysis indicated varying levels of desmin-positive cells in nine cases, whereas CD163- and CD68-positive cells were diffusely distributed in all 12 cases. We also performed double immunofluorescence staining and immunofluorescence in situ hybridisation in four resected cases with >10% desmin-positive tumour cells. The results suggested that the CD163-positive cells differed from desmin-positive cells with AHRR::NCOA2 fusion in all four cases.

CONCLUSION

Our findings suggested that AHRR::NCOA3 could be the second most frequent fusion gene, and histiocytic marker-positive cells are not genuine neoplastic cells in AFST.

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.

New molecular entities of soft tissue and bone tumors

PURPOSE OF REVIEW

The advances of molecular techniques have led to the refinement of the classification of mesenchymal tumors, leading to newly introduced entities in the recently published fifth edition of the WHO Classification of Soft Tissue and Bone Tumors, which are discussed in this review.

RECENT FINDINGS

For the first time, entities are included of which the name refers to the underlying molecular alteration including round cell sarcoma with EWSR1 -non-ETS fusions, CIC -rearranged sarcoma, and sarcoma with BCOR genetic alteration. EWSR1-SMAD3 -positive fibroblastic tumor and NTRK -rearranged spindle cell neoplasm are provisionally included as 'emerging' entities based on the underlying molecular alteration, though the entity still needs to be better defined. Other newly recognized entities are not named after their molecular change, but the molecular alteration helped to delineate them from others: atypical spindle cell/pleomorphic lipomatous tumor, anastomosing hemangioma, angiofibroma of soft tissue, myxoid pleomorphic liposarcoma, and poorly differentiated chordoma.

SUMMARY

Classification of mesenchymal tumors is increasingly based on the underlying molecular changes, although this cannot be interpreted separately from clinical, morphological, and immunohistochemical characteristics.

Angiofibroma of Soft Tissue: A Clinicopathological Study of Eight Cases With Emphasis on the Diagnostic Utility of Fluorescence In Situ Hybridization Detection for NCOA2 Rearrangement

Background

Angiofibroma of soft tissue (AFST) is a rare mesenchymal neoplasm of fibroblastic differentiation. Due to its diverse morphology and the lack of specific immunohistochemistry (IHC) markers, AFST could elicit a broad range of differential diagnosis. Several studies have disclosed in AFST recurrent gene fusions involving NCOA2, mainly AHRR–NCOA2 fusion, providing a useful approach to diagnosing this lesion. We report eight additional cases of this rare entity with emphasis on the diagnostic utility of fluorescence in situ hybridization (FISH) detection for NCOA2 rearrangement.

Methods

Clinicopathological data for eight AFSTs were retrieved. IHC was performed, and FISH was used to detect rearrangements involving NCOA2, DDIT3, and FUS loci.

Results

There were five female and three male patients, ranging in age from 29 to 69 years (median: 55 years). The patients presented mostly with a slow-growing mass in the extremities, with or without intermittent pain. All tumors were located in the lower extremities with three (27.5%) involving or adjacent to the knee joints. Tumor size ranged from 1.5 to 3.8 cm (median: 3.0 cm). Morphologically, the tumors consisted of a proliferation of uniform, bland spindle cells set in alternating myxoid and collagenous stroma with a prominent vascular network composed of countless small, branching, thin-walled blood vessels. Foci of “chicken wire”-like capillaries and medium- to large-sized blood vessels with prominent staghorn morphology were evident in two and four cases, respectively. In addition, sheets of small round cells and foci of cystic changes were observed in one each case. Degenerative nuclear atypia was identified in three cases, while mitosis and tumor necrosis were absent. By IHC, the stromal cells were variably positive for epithelial membrane antigen, desmin, and CD68. By FISH analysis, seven out of eight cases (87.5%) showed NCOA2 rearrangement, and the remaining one had increased gene copy numbers of intact NCOA2; rearrangements involving FUS (0/4) and DDIT3 (0/3) were not identified in the cases analyzed. All tumors were surgically removed, and none had recurrence at follow-up from 5 to 73 months.

Conclusions

FISH analysis for NCOA2 rearrangement represents a practical method for confirming the diagnosis of AFST on the basis of appropriate histomorphological backgrounds.

Angiofibroma of Soft Tissue on MRI and FDG PET/CT Image

ABSTRACT

Angiofibroma of soft tissue is a rare benign mesenchymal neoplasm. We reported a case of angiofibroma of soft tissue in a 61-year-old woman. MRI examination indicated a soft tissue mass in the right lower thigh, which showed isosignal intensity on T1-weighted imaging and heterogeneous high signal intensity on T2-weighted imaging. This lesion had intense tracer uptake, with an SUVmax of 7.24 on FDG PET/CT. Our case revealed that when soft tissue masses with intense FDG uptake on PET/CT are encountered, angiofibroma of soft tissue should be considered in the differential diagnosis.

Update on MR Imaging of Soft Tissue Tumors of Head and Neck

This article reviews soft tissue tumors of the head and neck following the 2020 revision of WHO Classification of Soft Tissue and Bone Tumours. Common soft tissue tumors in the head and neck and tumors are discussed, along with newly added entities to the classification system. Salient clinical and imaging features that may allow for improved diagnostic accuracy or to narrow the imaging differential diagnosis are covered. Advanced imaging techniques are discussed, with a focus on diffusion-weighted and dynamic contrast imaging and their potential to help characterize soft tissue tumors and aid in distinguishing malignant from benign tumors.

Recurrent Fusion of the GRB2 Associated Binding Protein 1 (GAB1) Gene With ABL Proto-oncogene 1 (ABL1) in Benign Pediatric Soft Tissue Tumors

BACKGROUND/AIM

Fusions of the ABL proto-oncogene 1 gene (ABL1 in 9q34) are common in leukemias but rare in solid tumors. The most notable is the t(9;22)(q34;q11)/BCR-ABL1 coding for a chimeric tyrosine kinase. We herein report an ABL1-fusion in a pediatric tumor.

MATERIALS AND METHODS

G-banding, fluorescence in situ hybridization, reverse transcription polymerase chain reaction and Sanger sequencing were performed on a soft tissue perineurioma found in the left musculus erector spinae of a child.

RESULTS

A der(4)t(4;9)(q31;q34) and a fusion of the GRB2 associated binding protein 1 (GAB1 in 4q31) gene with ABL1 were found. A literature search revealed 3 more cases with similar genetic and clinicopathological characteristics: a soft tissue perineurioma with t(2;9;4)(p23;q34;q31) and ABL1 rearrangement, a soft tissue angiofibroma with a GAB1-ABL1 chimeric gene, and a solitary fibrous tumor carrying a der(4)t(4;9)(q31.1;q34).

CONCLUSION

GAB1-ABL1 is a recurrent fusion gene in benign pediatric tumors.

Staging and Classification of Primary Musculoskeletal Bone and Soft Tissue Tumors Based on the 2020 WHO Update, From the AJR Special Series on Cancer Staging

Staging of primary musculoskeletal bone and soft tissue tumors is most commonly performed using the AJCC and the Enneking or Musculoskeletal Tumor Society (MSTS) staging systems. Radiologic imaging is integral in achieving adequate musculoskeletal neoplastic staging by defining lesion extent and identifying regional lymph node involvement and distant metastatic disease. Additional important features in surgical planning, though not distinct components of the staging systems, include cortical involvement, joint invasion, and neurovascular encasement; these features are optimally evaluated by MRI. In 2020, the WHO updated the classification of primary musculoskeletal tumors of soft tissue and bone. The update reflects the continued explosion in identification of novel gene alterations in many bone and soft tissue neoplasms. This has resulted in newly designated lesions, reclassification of lesion categories, and improved specificity of diagnosis. While radiologists do not need to have a comprehensive knowledge of the pathologic details, a broad working understanding of the most recent update is important to aid accurate and timely diagnosis given that histologic grading is a component of all staging systems. By approaching primary musculoskeletal neoplasms through a multidisciplinary approach with colleagues in pathology, orthopedic oncology, radiation oncology, and medical oncology, radiologists may promote improved diagnosis, treatment, and outcomes.

Ependymoma-like tumor with mesenchymal differentiation harboring C11orf95-NCOA1/2 or -RELA fusion: A hitherto unclassified tumor related to ependymoma

Recurrent fusion genes involving C11orf95, C11orf95‐RELA, have been identified only in supratentorial ependymomas among primary CNS tumors. Here, we report hitherto histopathologically unclassifiable high‐grade tumors, under the tentative label of “ependymoma‐like tumors with mesenchymal differentiation (ELTMDs),” harboring C11orf95‐NCOA1/2 or ‐RELA fusion. We examined the clinicopathological and molecular features in five cases of ELTMDs. Except for one adult case (50 years old), all cases were in children ranging from 1 to 2.5 years old. All patients presented with a mass lesion in the cerebral hemisphere. Histologically, all cases demonstrated a similar histology with a mixture of components. The major components were embryonal‐appearing components forming well‐delineated tumor cell nests composed of small uniform cells with high proliferative activity, and spindle‐cell mesenchymal components with a low‐ to high‐grade sarcoma‐like appearance. The embryonal‐appearing components exhibited minimal ependymal differentiation including a characteristic EMA positivity and tubular structures, but histologically did not fit with ependymoma because they lacked perivascular pseudorosettes, a histological hallmark of ependymoma, formed well‐delineated nests, and had diffuse and strong staining for CAM5.2. Molecular analysis identified C11orf95‐NCOA1, ‐NCOA2, and ‐RELA in two, one, and two cases, respectively. t‐distributed stochastic neighbor embedding analysis of DNA methylation data from two cases with C11orf95‐NCOA1 or ‐NCOA2 and a reference set of 380 CNS tumors revealed that these two cases were clustered together and were distinct from all subgroups of ependymomas. In conclusion, although ELTMDs exhibited morphological and genetic associations with supratentorial ependymoma with C11orf95‐RELA, they cannot be regarded as ependymoma. Further analyses of more cases are needed to clarify their differences and similarities.

Histopathological characteristics and CD163 immunostaining pattern in fibrous papule of the face

BACKGROUND

Signs of inflammation including epidermal interface changes, spongiosis, and dermal inflammation as well as pagetoid dyskeratosis are rarely described in fibrous papule (FP). We aimed to describe the inflammatory parameters, the rate of pagetoid dyskeratosis, along with CD163 immunohistochemical staining as an adjunctive diagnostic tool in FP.

METHODS

Histopathology samples of all biopsy-proven FP cases were retrieved from archives and investigated for inflammatory parameters, presence of pagetoid dyskeratosis, as well as CD163, CD10, and CD34 immunostaining pattern of dermal spindle/stellate or multinucleate cells (graded from 0 to 4).

RESULTS

Thirty-two cases of FP were identified. A high rate of inflammatory parameters including interface changes (20/32), spongiosis (31/32), and dermal lymphocytic inflammation (31/32) were detected. Pagetoid dyskeratosis was identified in eight out of 32 cases (25%). A grade 4 staining revealing a strong dendritic pattern was confirmed in all FP cases with CD163 immunohistochemistry including atypical variants such as granular FP, compared with CD10 (11/32) and CD34 (3/32).

CONCLUSION

The dendritic cellular proliferation in FP may represent an inflammatory response to various stimuli; pagetoid dyskeratosis is a relatively common and underrecognized epidermal feature and CD163 immunostaining may be used as an adjunctive diagnostic tool in unusual histopathological subtypes.