FOSL1 immunohistochemistry clarifies the distinction between desmoplastic fibroblastoma and fibroma of tendon sheath

Subcutaneous fibroblastoma resembling hemangioma: A case of benign tumor of the chest wall

Key Clinical Message

Desmoplastic fibroma presents similar to other soft tissue tumors to such an extent that even a gold standard investigation can miss.

Abstract

This is to report a mass in a 47-year-old male arising from the chest wall, which was first thought to be a hemangioma but was later diagnosed as a case of desmoplastic fibroblastoma with the help of a biopsy.

Superficial desmoplastic fibroblastoma (collagenous fibroma): Clinicopathologic study of 11 cases

BACKGROUND

Desmoplastic fibroblastoma (collagenous fibroma) is a rare soft tissue tumor that usually arises in the subcutis or skeletal muscle. Cases superficial to fascia are unusual and can cause diagnostic difficulty. We present 11 cases of superficial desmoplastic fibroblastoma involving a wide anatomic distribution.

METHODS

Archives were searched using the term "desmoplastic fibroblastoma" over a 10-year period (2012-2022). Cases superficial to fascia were retrieved, and available clinicopathologic features were recorded. Only cases involving the dermis were included.

RESULTS

Eleven cases were identified, all of which were received in consultation. Tumors involved the head and neck (2), lower extremity (2), back (2), foot (1), shoulder (1), axilla (1), hand (1), and breast (1). Each consisted of a hypocellular proliferation of bland stellate to spindled fibroblasts set in a collagenous to focally myxoid stroma. The immunohistochemical stains available for review demonstrated SMA positivity (4/7) and negative immunoreactivity for CD34 (0/6), EMA (0/3), desmin (0/3), and S100 (0/7).

CONCLUSIONS

Desmoplastic fibroblastoma may present superficially in the dermis to subcutis, posing a potential source of diagnostic difficulty. Recognition of the characteristic histopathologic features of desmoplastic fibroblastoma with judicial use of immunohistochemical stains should allow for accurate diagnosis.

Recurrent FOSL1 rearrangements in desmoplastic fibroblastoma

The FOS gene family has been implicated in tumourigenesis across several tumour types, particularly mesenchymal tumours. The rare fibrous tumour desmoplastic fibroblastoma is characterised by overexpression of FOSL1. However, previous studies using cytogenetic and molecular techniques did not identify an underlying somatic change involving the FOSL1 gene to explain this finding. Prompted by an unusual index case, we report the discovery of a novel FOSL1 rearrangement in desmoplastic fibroblastoma using whole-genome and targeted RNA sequencing. We investigated 15 desmoplastic fibroblastomas and 15 fibromas of tendon sheath using immunohistochemistry, in situ hybridisation and targeted RNA sequencing. Rearrangements in FOSL1 and FOS were identified in 10/15 and 2/15 desmoplastic fibroblastomas respectively, which mirrors the pattern of FOS rearrangements observed in benign bone and vascular tumours. Fibroma of tendon sheath, which shares histological features with desmoplastic fibroblastoma, harboured USP6 rearrangements in 9/15 cases and did not demonstrate rearrangements in any of the four FOS genes. The overall concordance between FOSL1 immunohistochemistry and RNA sequencing results was 90%. These findings illustrate that FOSL1 and FOS rearrangements are a recurrent event in desmoplastic fibroblastoma, establishing this finding as a useful diagnostic adjunct and expanding the spectrum of tumours driven by FOS gene family alterations. © 2022 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Fibroma of tendon sheath is defined by a USP6 gene fusion-morphologic and molecular reappraisal of the entity

Fibroma of tendon sheath (FTS) is an uncommon benign myofibroblastic neoplasm that arises in association with tenosynovial tissue. Fusions of the USP6 gene have been recently documented in a proportion of so-called "cellular FTS" but not in "classic FTS". It remains unknown whether FTS can be defined by a USP6 fusion, regardless of cellularity, and what are USP6 fusion-negative "cellular FTS". Furthermore, FTS with low cellularity seems to be frequently confused with desmoplastic fibroblastoma. We performed a comprehensive analysis, including targeted RNA sequencing, of 58 consecutive cases originally diagnosed as FTS (n = 49), desmoplastic fibroblastoma (n = 6), or nodular fasciitis (n = 3); the latter two at the predilection sites for FTS. After review of the original slides, 28 lesions were morphologically classified as FTS (13 "classic" and 15 "cellular") and 23 as desmoplastic fibroblastoma. Among originally diagnosed FTS at the more cellular end of the spectrum, we identified seven lesions that shared many morphologic features of FTS but, in addition, showed several distinct morphologic features consistent with myofibroma, such as myoid appearance, branching thin-walled vessels, and perivascular growth. Targeted RNA sequencing showed a USP6 fusion in 17 of 18 analyzed FTS, regardless of cellularity, 0 of 5 desmoplastic fibroblastomas and 0 of 4 myofibromas. MYH9, COL1A1, and ASPN were identified as fusion partners in three cases each, and MIR22HG, CTNNB1, SPARC, CAP1, EMP1, LINC00152, NR1D1, and RAB1A in a single case each. FTS, regardless of cellularity, can be defined by a USP6 fusion with a variety of fusion partners. More cellular lesions exhibiting some morphologic features of FTS but lacking a USP6 fusion tend to be myofibromas.

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.

Symmetrical palatal fibromatosis: An additional case report with immunohistochemical characterization

BACKGROUND

The term "symmetrical palatal fibromatosis" was recently suggested to designate bilateral palatal lesions presenting as typically broad, "mirror" images on the posterior lateral region of the hard palate.

PURPOSE

We report an additional case of this as-yet poorly understood oral lesion in a 67-year-old male patient, with emphasis on differential diagnoses and immunohistochemical characterization.

CASE REPORT

The histopathological examination demonstrated a hypocellular, fibrous connective tissue with prominent thick collagen bundles and few blood vessels. Scattered large, stellate, and sometimes binucleated fibroblasts were found. Immunohistochemistry was positive for vimentin and negative for smooth muscle actin, S-100, desmin, HHF-35, AE1-AE3, Factor XIIIa, CD68, and FOSL1. This is the second study to show the immunohistochemical profile, with emphasis in FOSL1, of an additional case of symmetrical palatal fibromatosis.

CONCLUSIONS

We encourage further reports about this entity, especially in relation to immunohistochemical and molecular features, so far poorly described, but very important for better recognition of this entity. Key words:Palate, symmetrical palatal fibromatosis, desmoplastic fibroblastoma, immunohistochemistry.

Desmoplastic Fibroblastoma Invading the Humerus

Desmoplastic fibroblastoma (DFB) is an uncommon, benign, soft tissue tumor. The tumor most often presents as a slowly growing, painless soft tissue mass and is usually small. There have been only a few reports of patients with DFB who presented with bone invasion. Herein, we report the case of a 66-year-old woman with DFB with bone invasion in her left axilla. A lump under the left axilla was detected and was associated with pain and limited range of motion (ROM) of the shoulder. Computed tomography showed a soft tissue mass with invasion of the adjacent left humerus. Magnetic resonance imaging revealed a lesion with low signal intensity on T1- and T2-weighted images, and weak internal enhancement on postcontrast T1-weighted images with fat suppression. Histologic evaluation of a preoperative needle biopsy revealed DFB with FOSL1 expression. The tumor was marginally excised. Postoperative outpatient follow-up demonstrated a significant improvement in pain and ROM of the shoulder and no recurrence after 1 year. Even though DFB with bone invasion can cause pronounced clinical symptoms with pain and limited ROM, we conclude that simple excision is an adequate treatment.

Diagnosis and Differential Diagnosis of Desmoplastic Fibroblastoma by Clinical, Radiological, and Histopathological Analyses

Background:

Desmoplastic fibroblastoma (collagenous fibroma) is an uncommon benign soft-tissue tumor, rarely involving bone. It shares some overlapping features with other infiltrate tumors, such as desmoid-type fibromatosis, neurofibroma, and low-grade fibromyxoid sarcoma. The misdiagnosis may cause unnecessary surgical overtreatment, especially for those involving bone. In order to deepen the understanding of the diagnosis and differential diagnosis of desmoplastic fibroblastoma, we planned to analyze the clinical, radiological, and histopathological features and the outcome of desmoplastic fibroblastoma on the basis of case analysis and literature review.

Methods:

Sixteen cases were retrieved from the surgical pathology records from May 2011 to April 2016 in the Department of Pathology in Beijing Jishuitan Hospital. Formalin-fixed, paraffin-embedded specimens of 16 cases of desmoplastic fibroblastoma were collected. Hematoxylin and eosin stain and immunohistochemistry were used to observe the histological features of desmoplastic fibroblastoma of soft tissue and bone. The images for diagnosis obtained from the ultrasonic examination, X-ray, magnetic resonance imaging, and computed tomography were used to observe the radiological features. Related literatures were retrieved from the PubMed and CNKI databases.

Results:

Sixteen cases of desmoplastic fibroblastoma of soft tissue were located in the hand (n = 7), foot (n = 4), upper arm (n = 1), shoulder (n = 1), forearm (n = 2), and one case occurred in the proximal femur. Age ranged from 32 to 82 years (median age: 58 years). There were six females and ten males. Histologically, the lesions of soft tissue appeared as well-circumscribed masses with abundant collagenous matrix and low vascularity. Tumor cells were stellate- or spindle-shaped and uniformly distributed within the extracellular matrix. In five cases, the desmoplastic fibroblastoma were found to have infiltrated into the skeletal muscle tissue. In one case of desmoplastic fibroblastoma of bone, radiographs revealed osteolytically well-defined lesion. Immunohistochemistry stain showed that vimentin and smooth muscle actin were positive in all cases of desmoplastic fibroblastoma.

Conclusions:

Desmoplastic fibroblastoma (collagenous fibroma) has prominent clinical, histopathological, and radiological features. Before the differential diagnosis from other tumors is obtained by thorough analysis and comparison of the similar and different characteristics, the appropriate surgical management and accurate prognosis evaluation could not be delivered to the patient.

Desmoplastic fibroblastoma of the left upper arm

An elderly female patient presented to the clinic with a several-week history of a mass in her left upper arm that was tender to the touch. The mass was initially thought to be a schwannoma of the left radial nerve based on imaging and was surgically removed. The pathology report revealed an uncommon diagnosis of desmoplastic fibroblastoma.