Deep "benign" fibrous histiocytoma: clinicopathologic analysis of 69 cases of a rare tumor indicating occasional metastatic potential

Clinicopathologic and molecular study of superficial CD34-positive fibroblastic tumours mimicking atypical fibrous histiocytoma (dermatofibroma)

AIMS

Superficial CD34-positive fibroblastic tumour (SCD34FT) is an uncommon but distinctive low-grade neoplasm of the skin and subcutis that shows frequent CADM3 expression by immunohistochemistry (IHC). In this study, prompted by an index case resembling 'atypical fibrous histiocytoma (FH)' that was positive for CADM3 IHC, we systematically examined a cohort of tumours previously diagnosed as 'atypical FH' by applying CADM3 and fluorescence in situ hybridization (FISH) for PRDM10 rearrangement, to investigate the overlap between these tumour types.

METHODS AND RESULTS

Forty cases of atypical FH were retrieved, including CD34-positive tumours (n = 20) and CD34-negative tumours (n = 20). All tumours were stained for CADM3. All CADM3-positive tumours were evaluated by FISH to assess for PRDM10 rearrangement. Eleven CD34-positive tumours (11/20, 55%) coexpressed CADM3 and were reclassified as SCD34FT. None (0/20) of the CD34-negative atypical FH were CADM3-positive. Reclassified SCD34FT (10/11) arose on the lower extremity, with frequent involvement of the thigh (n = 8). Features suggestive of atypical FH were observed in many reclassified cases including variable cellularity, spindled morphology, infiltrative tumour margins, collagen entrapment, epidermal hyperpigmentation, and acanthosis. Variably prominent multinucleate giant cells, including Touton-like forms, were also present. An informative FISH result was obtained in 10/11 reclassified tumours, with 60% (6/10) demonstrating PRDM10 rearrangement.

CONCLUSION

A significant subset of tumours that histologically resemble atypical FH, and are positive for CD34, coexpress CADM3 and harbour PRDM10 rearrangement, supporting their reclassification as SCD34FT. Awareness of this morphologic overlap and the application of CADM3 IHC can aid the distinction between SCD34FT and atypical FH.

Fast-Growing Frontal Subcutaneous Nodule in a Young Woman

A woman in her 20s presented with a firm, mobile, painful, fast-growing subcutaneous nodule in the glabella. What is your diagnosis?

High-Frequency Ultrasound Imaging to Distinguish High-Risk and Low-Risk Dermatofibromas

BACKGROUND

Dermatofibroma has various pathological classifications, some of which pose a risk of recurrence and metastasis. Distinguishing these high-risk dermatofibromas based on appearance alone can be challenging. Therefore, high-frequency ultrasound may provide additional internal information on these lesions, helping to identify high-risk and low-risk dermatofibroma early.

METHODS

In this retrospective study, 50 lesions were analyzed to explore the correlation between clinical and high-frequency ultrasound features and dermatofibroma risk level. Based on their pathological features, the lesions were divided into high-risk (n = 17) and low-risk (n = 33) groups. Subsequently, an identification model based on significant high-frequency ultrasound features was developed.

RESULTS

Significant differences were observed in the thickness, shape, internal echogenicity, stratum basal, and Doppler vascular patterns between the high-risk and low-risk groups. The median lesion thickness for the high-risk dermatofibroma group was 4.1 mm (IQR: 3.2-6.1 mm), while it was 3.1 mm (IQR: 1.3-4.2 mm) for the low-risk dermatofibroma group. In the high-risk dermatofibroma group, irregular morphology was predominant (70.6%, 12/17), the most common being dermis-to-subcutaneous soft tissue penetration (64.7%, 11/17), and heterogenous internal echogenicity was observed in the majority of cases (76.5%, 13/17). On the other hand, regular morphology was more prevalent in the low-risk dermatofibroma group (78.8%, 26/33), primarily limited to the dermis layer (78.8%, 26/33), with homogeneous internal echogenicity also being prevalent in the majority of cases (81.8%, 27/33). Regarding the Doppler vascularity pattern, 69.7% (23/33) of low-risk dermatofibromas had no blood flow, while 64.7% (11/17) of high-risk dermatofibromas had blood flow.

CONCLUSION

High-frequency ultrasound is crucial in distinguishing high-risk and low-risk dermatofibromas, making it invaluable for clinical management.

Deep fibrous histiocytoma of the index finger: a case report

Our patient presented with an elastic soft mass of his left index finger. Hematoxylin and eosin staining showed a high cellular density with spindle-shaped cells in a storiform pattern. Immunohistochemical staining was positive for CD68, factor XIIIa and α-smooth muscle actin, and negative for CD34, STAT6, S100 protein, and desmin.

Clinicopathologic Features of Facial Dermatofibromas, a Cohort Study, and a Systematic Review of Literature

BACKGROUND

Dermatofibromas are common skin tumors that typically occur on the extremities and trunk and demonstrate benign behavior, frequent recurrences, and very rare metastasis. Facial dermatofibromas are rare and not well studied . We analyzed clinicopathologic features of facial dermatofibromas.

DESIGN

Considering the rarity of the condition, we conducted a cohort study and a systematic review. We queried medical records of a single tertiary care center for dermatofibromas from January 1, 2000, to July 1, 2021. A systematic review of multiple databases was conducted through October 27, 2021, to include studies reporting facial dermatofibromas. Random-effects meta-analysis was used to estimate pooled odds ratio and proportions with associated 95% confidence interval (CI).

RESULTS

The cohort study identified 2858 cases of dermatofibromas, of which, 23 cases from 18 patients were on the face (1%). The mean age was 52.7 ± 17.8 years. Fifty-six percent of the cases were women. The most common location was the forehead (6 cases). The mean follow-up was 54 months. Forty-four percent of the cases had subcutaneous involvement, and 39% were the cellular type. Margins were positive in 89% of the cases, recurrence rate was 22%, and no metastases were observed. The systematic review included 10 studies (119 patients). Meta-analyses showed that facial dermatofibromas were 2% of all dermatofibromas (95% CI: 1%-3%). The local recurrence rate was 14% (95% CI: 6%-26%). Facial dermatofibromas with subcutaneous involvement were more likely to recur [odds ratio 4.53 (95% CI: 1.12-18.24)]. Before histopathologic examination, clinical differential diagnosis included dermatofibromas in only 9% of the cases (95% CI: 2%-19%).

CONCLUSION

Facial dermatofibromas are rare and are difficult to fully excise. Cellular type and subcutaneous or muscular involvement are common in these cases and tend to have higher local recurrence rate than other nonfacial dermatofibromas. Wider excisions might be necessary for complete excision.

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.

Mesenchymal Tumors of the Mediastinum: An Update on Diagnostic Approach

Mesenchymal tumors of the mediastinum are a heterogenous group of rare tumors with divergent lineages. Mediastinal mesenchymal tumors are diagnostically challenging due to their diversity and morphologic overlap with nonmesenchymal lesions arising in the mediastinum. Accurate histologic diagnosis is critical for appropriate patient management and prognostication. Many mediastinal mesenchymal tumors affect distinct age groups or occur at specific mediastinal compartments. Neurogenic tumors, liposarcoma, solitary fibrous tumor, and synovial sarcoma are common mesenchymal tumors in the mediastinum. Herein, we provide an update on the diagnostic approach to mediastinal mesenchymal tumors and a review of the histologic features and differential diagnosis of common benign and malignant mesenchymal tumors of the mediastinum.

Imaging of Pediatric Soft Tissue Tumors and Tumor-like Conditions

Lumps and bumps are frequently seen in children, and the vast majority are a result of trauma, infection, or inflammation. True soft tissue neoplastic lesions are rare; however, their wide and complex classifications make these lesions challenging to manage. Imaging features are usually nonspecific, and a reasonable list of differential diagnoses can be generated following consideration of the clinical presentation, age, and anatomical location of the lesion. In this article, we offer a practical approach to diagnosing such lesions by discussing the most common three benign and malignant lesions in different anatomical regions stratified by age with emphasis on certain features that might aid in the diagnosis such as depth, multiplicity, calcification, or other specific imaging feature.

Aneurysmal Fibrous Histiocytoma: A Large Soft Tissue Tumor with Metastases Treated with Palliative Radiation Therapy and Targeted Therapy

Aneurysmal fibrous histiocytoma (AFH) is a rare variant of cutaneous fibrous histiocytoma, with low malignant potential and infrequent metastatic progression. We present the case of a 19-year-old female with a large AFH of the neck metastatic to soft tissue and treated with radiation therapy and molecularly targeted therapy. To our knowledge, this is the first report describing either radiation therapy and palliation or the use of targeted therapy in this uncommon malignancy and can provide insight into future therapeutic strategies.

Perineural Invasion as a Clue to Malignant Behavior in a Dermatofibroma

Dermatofibroma (DF) represents one of the most common mesenchymal proliferations of the skin. Their recurrence rate, even when incompletely excised, is very low, whereas the atypical, aneurysmal, and cellular variants have recurrence rates of up to 20% each. Extraordinary rare malignant lesions with metastases to lymph nodes and/or lung have been described. We report a 64-year-old woman with a long history (years) of a skin lesion on her right arm that became painful during the last months. Histologically, it consisted of a conventional cellular DF in which perineural invasion was present. Subsequently, the lesion showed a clinically aggressive course with recurrences, sarcomatous transformation, and pulmonary metastases. Given that no predictive morphological features have been identified to separate classical benign DF from rare metastasizing forms, perineural invasion in an otherwise conventional DF could be a histopathologic clue for an adverse prognosis and should provoke a closer clinical follow-up.

Endoscopic submucosal dissection of tracheal deep benign fibrous histiocytoma using hybrid knife

Deep benign fibrous histiocytoma (FH) is an uncommon and poorly recognized tumor that arises in subcutaneous or deep soft tissue. Deep benign FH of the trachea is even more rare. Deep benign FH recurs in approximately 20% of cases, so surgical resection is the recommended treatment for FH. However, some patients are afraid of the trauma and potential complications from the resection of tracheal tumors, so they do not accept surgical resection. With the development of interventional pulmonology, bronchoscopic intervention plays a key role in the treatment of benign tracheal tumors. Novel tools have emerged in interventional pulmonology and optimized the traditional techniques. Here, we report a case of deep benign FH of the trachea with broad base relapse after electrocautery with snare, argon plasma coagulation (APC) and radiotherapy. It was treated successfully by endobronchial resection with a hybrid knife (HK) and APC. The HK is a hybrid device that combines an electrocautery knife with a water jet in one instrument. Submucosal injection and circumferential cutting and dissection of lesions as well as coagulation of bleeding can be performed only with the HK. During the 6 months follow-up, the deep benign FH of the trachea did not relapse. In the case reported herein, the HK enabled submucosal injection and circumferential cutting and dissection of lesions as well as access to submucosal lesions to gain further adequate APC treatment, thereby allowing a better clinical response than that achieved by traditional electrocautery with snare and APC. In conclusion, the HK with a water jet is a feasible and effective endoscopic method for management for benign or low-grade malignant neoplasms of the trachea, especially those with a wide base and submucosal involvement.

38-year-old woman with nasal congestion: A rare case of septum-originated benign fibrous histiocytoma

INTRODUCTION

Benign fibrous histiocytoma (BFH) is a mesenchymal tumor composed of fibroblasts and histiocytes, which normally occurs in the bone tissue and/or the skin of the limbs. BFH of the nasal septum is rare worldwide.

PATIENT CONCERNS

A 38-year-old female patient attended our clinic with congestion in her right nasal cavity.

DIAGNOSES

Endoscopic examination revealed a mass within the right nasal passage. Immunohistochemical staining demonstrated cells labeled with VIM (+), CD68PGM1 (+), CD34 (-), Actin (-), PCK (-), EMA (-), Desmin (-), SMA (-), S-100 (-), P63 (-), ALK-1 (-), beta-catenia (+), and KI67 (+). Clinical and histopathological examinations showed that the mass was a septum-originated BFH.

INTERVENTIONS

For the treatment of BFH of the nasal septum, the mass was removed endoscopically using a transnasal approach.

OUTCOMES

No recurrence was observed over 30 months of follow-up.

CONCLUSION

To prevent the recurrence wide local resection with histological clear margin and long-term follow-up with an endoscope are necessary.

Deep benign fibrous histiocytoma occurring in the kidney: Case report

RATIONALE

Deep benign fibrous histiocytoma (BFH) is relatively rare in contrast to superficial BFH involving the skin. Moreover, it was extremely rare for deep BFH occurring in the solid organ. To our knowledge, so far, only one case of deep BFH of the kidney was reported in English literature.

PATIENT CONCERNS

Herein, we report another case of deep BFH located in the kidney in a 88-year-old female. She was referred to our hospital for a severe pain in the right upper abdomen. Computed tomography revealed a round low-density shadow measuring 6 cm in the kidney.

DIAGNOSIS

The lesion was diagnosed as a deep BFH of the kidney, as the tumor was histologically predominately composed of bland ovoid cells arranged in a storiform pattern.

INTERVENTION

The patient underwent the total resection of the right kidney with the tumor in our hospital.

OUTCOMES

The postoperative course was uneventful. The patient was alive with no tumor recurrence or metastasis within 6 months of follow-up.

LESSONS

We present another case of deep BFH of the kidney. Because of the rarity, the tumor may be poorly recognized. The typical storiform pattern in histology may be helpful for diagnosis. This report serves to remind that deep BFH is also a differential diagnosis for a tumor with storiform pattern in the kidney.

PRDM10-rearranged Soft Tissue Tumor: A Clinicopathologic Study of 9 Cases

Gene fusion transcripts containing PRDM10 were recently identified in low-grade undifferentiated pleomorphic sarcomas (UPS). Here, we describe the morphologic and clinical features of 9 such tumors from 5 men and 4 women (age: 20 to 61 y). Three cases had previously been diagnosed as UPS, 3 as superficial CD34-positive fibroblastic tumor (SCD34FT), 2 as pleomorphic liposarcoma, and 1 as pleomorphic hyalinizing angiectatic tumor. The tumors were located in the superficial and deep soft tissues of the thigh/knee region (4 cases), shoulder (2 cases), foot, trunk, and perineum (1 case each) ranging in size from 1 to 6 cm. All showed poorly defined cellular fascicles of pleomorphic cells within a fibrous stroma with frequent myxoid change and a prominent inflammatory infiltrate. All displayed highly pleomorphic nuclear features, but a low mitotic count. Most tumors were well circumscribed. One of 9 tumors recurred locally, but none metastasized. Immunohistochemically, all were CD34 and showed nuclear positivity for PRDM10; focal positivity for cytokeratins was seen in 5/6 cases. PRDM10 immunoreactivity was evaluated in 50 soft tissue tumors that could mimic PRDM10-rearranged tumors, including 4 cases exhibiting histologic features within the spectrum of SCD34FT. Except for 2/6 pleomorphic liposarcomas and 1/4 myxofibrosarcomas, other tumors did not show nuclear positivity but displayed weak to moderate cytoplasmic immunoreactivity. In conclusion, PRDM10-rearranged soft tissue tumor is characterized by pleomorphic morphology and a low mitotic count. Its morphologic spectrum overlaps with SCD34FT. Clinical features of this small series suggest an indolent behavior, justifying its distinction from UPS and other sarcomas.

Dupuytren's disease in a child: a long-term evolution after surgery

We report the case of a 13-year-old girl who presented with a fibrous nodular lesion on the palm of her hand. After ultrasonographic examination, surgical resection of the skin (dermofasciectomy) was performed, and a nodular phase mass was recovered, characterized as fusocellular fibroblast proliferation in a dense collagenous stroma with a cell population consisting of parallel fascicles of densely packed fusiform cells of a fibroblast strain. No signs of encapsulation or malignant changes were observed, all of which was consistent with Dupuytren's disease. This lesion is exceptional in childhood. Sixteen years later, the patient has not relapsed, and retains full active and passive mobility. Dupuytren's disease in childhood must be considered in the differential diagnosis of any hard palmar lesion. Diagnostic uncertainty and the fact that a hard palmar lesion in children may be clinically indistinguishable from a malignant process mean that resection of the lesion and histological examination are required.

Cutaneous Spindle Cell Neoplasms: Pattern-Based Diagnostic Approach

Context.—

Spindle cell neoplasms arising in the skin comprise a heterogeneous group of tumors with divergent lineages. Cutaneous spindle cell neoplasms are relatively common and present surgical pathologists with diagnostic challenges. Recognition of their histopathologies is important for correct diagnosis and management. The current review presents a pattern-based diagnostic approach to common cutaneous spindle cell neoplasms that often cause diagnostic difficulties.

Objective.—

To provide a useful guide for diagnosis of cutaneous spindle cell neoplasms.

Data Sources.—

PubMed (US National Library of Medicine) reports and the authors' personal experiences are reviewed.

Conclusions.—

The authors briefly summarize the histologic features and differential diagnoses of common cutaneous spindle cell neoplasms.

Epithelioid cell histiocytoma with SQSTM1-ALK fusion: a case report

Background

Epithelioid cell histiocytoma (ECH), which is also known as epithelioid benign fibrous histiocytoma, has been classified as a rare variant of fibrous histiocytoma (FH). However, the recent detection of ALK protein expression and/or ALK gene rearrangement in ECH suggests that it might be biologically different from conventional FH.

Case presentation

A 27-year-old male presented with nodule on his left foot, which had been present for 5 years. A macroscopic examination revealed an exophytic, hyperkeratotic nodule on the dorsum of the left foot. Tumorectomy was performed, and a microscopic examination showed a subepidermal lesion composed of sheets of tumor cells with oval to round nuclei and ill-defined eosinophilic cytoplasm. The tumor cells were diffusely positive for factor XIIIa and ALK, but were negative for AE1/AE3 keratin, alpha-smooth muscle actin, CD30, CD34, CD68, PU.1, melan A, MITF, and S-100 protein. ALK immunostaining showed a diffuse cytoplasmic staining pattern. ALK fluorescence in situ hybridization demonstrated break-apart signals, which was suggestive of ALK rearrangement. A 5′-rapid amplification of cDNA ends assay detected SQSTM1-ALK fusion, in which exon 5 of the SQSTM1 gene was fused to exon 20 of the ALK gene. The patient was free from recurrence and distant metastasis at the 1-year of follow-up.

Conclusion

We were able to demonstrate the SQSTM1-ALK fusion gene in ECH. Practically, detecting immunopositivity for ALK and appropriate cell-lineage markers are the key to diagnosing ECH.

Dermatofibroma: sonographic findings and pathologic correlation

Background Ultrasound has been increasingly used for the evaluation of superficial soft tissue lesions. Dermatofibroma is one of the most common dermal lesions. Experiences in ultrasound examinations of dermatofibromas have been accumulated. Purpose To evaluate sonographic findings of dermatofibroma and to correlate them with pathologic findings. Material and Methods A total of 18 dermatofibromas in 15 patients were included. Sonographic findings were assessed for location, depth, size, shape, margin, spiculation, echogenicity, internal hyperechoic dots, change in echogenicity of adjacent soft tissue, and vascularity, by two musculoskeletal radiologists in consensus. Pathologic findings were evaluated by one pathologist. Ultrasonographic characteristics were correlated with the pathologic findings by discussion between one radiologist and one pathologist. Results On ultrasound, all lesions were found to be located in the dermis, and 14 lesions (78%) extended into the subcutaneous layer. Mean size was 7 mm (range = 3 to 10 mm). Characteristic findings were ill-defined margins (n = 15, 83%), spiculated margins (n = 12, 67%), change in echogenicity of adjacent soft tissue (n = 14, 78%), and no Doppler flow (n = 14, 78%). Histologically, depth, margin, and spiculation were correlated with sonographic findings. Reactive fibrosis and chronic inflammation were seen in adjacent dermis and subcutaneous fat layer of echogenicity change. Conclusion On ultrasound, dermatofibromas are usually visible as avascular dermal lesions with extension into the subcutaneous layer, and are characterized by ill-defined margins, marginal spiculation, and change in echogenicity of surrounding soft tissues.

Nonepithelial Tumors and Tumor-like Lesions of the Skin and Subcutis in Children

This overview of mesenchymal tumors presenting in the skin and/or subcutis in children brings together the range of neoplasms and hamartomas which are seen in this age-group. It is not surprising from the perspective of the pediatric or general surgical pathologist that vascular anomalies, including true neoplasms and vascular malformations, are the common phenotypic category. Since there is considerable morphologic overlap among these lesions, clinicopathologic correlation may be more important than for many of the other mesenchymal tumors. The skin and subcutis are the most common sites of clinical presentation for the infantile myofibroma which is the most common of fibrous mesenchymal tumors in children. Several of the other mesenchymal tumors are more common adults-like dermatofibrosarcoma protuberans, but nonetheless have an important presence in children, even as a congenital neoplasm. A lipomatous tumor in a young child should be considered as a possible manifestation of an overgrowth syndrome.

A case of giant cell-rich solitary fibrous tumor in the external auditory canal

We present a rare case of giant cell-rich solitary fibrous tumor (SFT) arising at the left external auditory canal in a 31-year-old woman. The tumor was well-circumscribed and composed of spindle-shaped cells with abundant collagenous bands. Scattered multinucleate giant cells were observed, some of which lined pseudovascular spaces. Although a focal mild-hypercellular area was observed, mitoses were rare and necrosis was absent. Interstitial mast cells were scattered, especially in the hypercellular area. Immunohistochemically, CD34, vimentin, and Bcl-2 presented diffuse positivity. Moreover, both mononuclear spindle cells and multinucleate cells showed nuclear STAT6 positivity, while NAB2-STAT6 fusion gene could not be detected by reverse transcription polymerase chain reaction using formalin-fixed specimen. These findings suggest the pathological diagnosis of giant cell-rich SFT, previously known as giant cell angiofibroma, which is a rare variant of SFT with multinucleate giant cells and occurs predominantly in orbital region. Although giant cell-rich SFTs of extra-orbital sites have been reported, to our knowledge, this is the first case arising in the external auditory canal. Giant cell-rich SFT should be considered as a differential diagnosis of spindle cell lesion with multinucleate giant cells, and STAT6 immunohistochemistry should be performed to distinguish this rare tumor from other mesenchymal neoplasms.

Deep Penetrating Fibrous Histiocytoma: A Case Report and Implications for Surgical Management

Deep penetrating fibrous histiocytoma (DPFH) is a rare variant of fibrous histiocytoma that can arise in the subcutis and deep soft tissues with different clinical implications from dermatofibromas. Dermatofibromas are mainly cosmetic annoyances and do not require surgical management. However, the DPFH does require that negative surgical margins be achieved because of the possibility of local recurrence and distant metastasis. We describe a case of a 24-year-old man diagnosed with DPFH through histologic examination and immunohistochemistry. The lesion displayed diffuse, strong D2-40 positivity and a minority of cells were highlighted with factor XIIIa. The lesion was negative for CD34. The patient's lesion was incompletely excised and a repeat excision was required.

Benign fibrous histiocytoma arising at the temporal bone of an infant--case report and review of the literature

PURPOSE

We report a very rare case of a fast-growing benign fibrous histiocytoma at the temporal bone.

METHODS

A 1-year-old girl was referred for investigation of a right temporal mass that increased during 2-week observation. Imaging studies showed a lytic, loculated skull tumor at the left temporal bone. On magnetic resonance imaging scans, the tumor was isointense on T1- and relatively high-intense on T2-weighted images. The tumor was mostly homogeneously enhanced by gadolinium. On diffusion-weighted images, it was iso- to relatively low-intense; perfusion-weighted images revealed low perfusion.

RESULTS

Complete macroscopic resection of the tumor was performed. Immunohistochemical analysis showed that the tumor was positive for CD68 and α-smooth muscle actin and negative for CD1a and CD34; the MIB-1 labeling index was 4 %. A diagnosis of primary benign fibrous histiocytoma of the skull was made. At 6-month follow-up, there were no clinical or radiological signs of tumor recurrence and/or metastasis.

CONCLUSIONS

We review the clinical, radiological, and immunohistochemical characteristics of benign fibrous histiocytoma at the skull.

Gene fusion detection in formalin-fixed paraffin-embedded benign fibrous histiocytomas using fluorescence in situ hybridization and RNA sequencing

Benign fibrous histiocytomas (FH) can be subdivided into several morphological and clinical subgroups. Recently, gene fusions involving either one of two protein kinase C genes (PRKCB and PRKCD) or the ALK gene were described in FH. We here wanted to evaluate the frequency of PRKCB and PRKCD gene fusions in FH. Using interphase fluorescence in situ hybridization on sections from formalin-fixed paraffin-embedded (FFPE) tumors, 36 cases could be analyzed. PRKCB or PRKCD rearrangements were seen in five tumors: 1/7 regular, 0/3 aneurysmal, 0/6 cellular, 2/7 epithelioid, 0/1 atypical, 2/10 deep, and 0/2 metastatic lesions. We also evaluated the status of the ALK gene in selected cases, finding rearrangements in 3/7 epithelioid and 0/1 atypical lesions. To assess the gene fusion status of FH further, deep sequencing of RNA (RNA-Seq) was performed on FFPE tissue from eight cases with unknown gene fusion status, as well as on two FH and six soft tissue sarcomas with known gene fusions; of the latter eight positive controls, the expected fusion transcript was found in all but one, while 2/8 FH with unknown genetic status showed fusion transcripts, including a novel KIRREL/PRKCA chimera. Thus, also a third member of the PRKC family is involved in FH tumorigenesis. We conclude that gene fusions involving PRKC genes occur in several morphological (regular, cellular, aneurysmal, epithelioid) and clinical (cutaneous, deep) subsets of FH, but they seem to account for only a minority of the cases. In epithelioid lesions, however, rearrangements of PRKC or ALK were seen, as mutually exclusive events, in the majority (5/7) of cases. Finally, the study also shows that RNA-Seq is a promising tool for identifying gene fusions in FFPE tissues.

LAMTOR1-PRKCD and NUMA1-SFMBT1 fusion genes identified by RNA sequencing in aneurysmal benign fibrous histiocytoma with t(3;11)(p21;q13)

RNA sequencing of an aneurysmal benign fibrous histiocytoma with the karyotype 46,XY,t(3;11)(p21;q13),del(6)(p23)[17]/46,XY[2] showed that the t(3;11) generated two fusion genes: LAMTOR1-PRKCD and NUMA1-SFMBT1. RT-PCR together with Sanger sequencing verified the presence of fusion transcripts from both fusion genes. In the LAMTOR1-PRKCD fusion, the part of the PRKCD gene coding for the catalytic domain of the serine/threonine kinase is under control of the LAMTOR1 promoter. In the NUMA1-SFMBT1 fusion, the part of the SFMBT1 gene coding for two of four malignant brain tumor domains and the sterile alpha motif domain is controlled by the NUMA1 promoter. The data support a neoplastic genesis of aneurysmal benign fibrous histiocytoma and indicate a pathogenetic role for LAMTOR1-PRKCD and NUMA1-SFMBT1.

Sebaceous induction in dermatofibroma: a common feature of dermatofibromas on the shoulder

BACKGROUND

Dermatofibroma (DF) has multiple histopathological variants and overlying acanthosis, hyperkeratosis and hyperpigmentation are often present. We have frequently observed sebaceous induction in DFs on the shoulder and wanted to assess if this is a site-specific finding.

METHODS

We prospectively collected 100 DFs and assessed for sebaceous induction, the histopathologic pattern of the DF and any associated-epidermal changes. We retrospectively searched for DFs with sebaceous induction to assess the anatomic site of the biopsy.

RESULTS

In the 100 prospectively collected DFs, 49% occurred on the lower extremities, 39% on the upper extremities, 10% on the trunk and 2% on the head. Sebaceous induction was present in 16 DFs, 81% of which occurred on or near the shoulder. The most common variant was fibrocollagenous DF (64%), including in DFs with sebaceous induction. The retrospective search for DFs with sebaceous induction found 19 cases in which 95% occurred on the shoulder area. Sclerotic pattern DFs were most common in this retrospective cohort (47%), and seborrheic keratosis-like hyperplasia occurred in 100% of these cases.

CONCLUSION

DFs occurring on the shoulder have a high incidence of sebaceous induction with seborrheic keratosis-like epidermal hyperplasia and a fibrocollagenous or sclerotic pattern.

Recently characterized soft tissue tumors that bring biologic insight

Previously unrecognized but clinicopathologically (and often molecularly) distinct types of soft tissue tumor continue to be characterized, allowing wider recognition, more consistent application of diagnostic criteria, more reliable prediction of tumor behavior and enhancement of existing classification schemes. Examples of such 'entities' that have become much better understood over the past decade or so include deep 'benign' fibrous histiocytoma, hemosiderotic fibrolipomatous tumor, PEComa, spindle cell liposarcoma, myoepithelial tumors of soft tissue and spindle cell/sclerosing rhabdomyosarcoma. These tumor types, as well as the insights which they have engendered, are briefly reviewed here.

Metastasizing "benign" cutaneous fibrous histiocytoma: a clinicopathologic analysis of 16 cases

Cutaneous fibrous histiocytoma (FH) is considered a benign tumor; however, certain types of FH have been shown to have a tendency for local recurrence, and there are rare reported cases of metastasis. In this study, 16 cases of morphologically benign FH with locoregional or distant metastasis were identified in consult files. Pathologic features of primary, recurrent, and metastatic tumors, as well as clinical outcome, were evaluated. Nine were male and 7 were female patients; mean age was 42 years (range, 3 to 68 y). Primary tumors arose on the leg in 5 patients, buttock in 1, trunk in 3, shoulder in 3, neck in 2, and finger in 1. The primary site in 1 case was unknown. Fifteen primary tumors available for review involved the dermis; 6 extended into the superficial subcutis. Tumor size ranged from 1 to 5 cm (median 3.2 cm). Histologically, primary tumors showed characteristic features of FH, being composed in most cases of a polymorphous population of bland spindle and histiocytoid cells in a mixed storiform and fascicular growth pattern with admixed foam cells, multinucleate cells, and inflammatory cells in varying proportions. Histologic variants included 11 cellular (2 with mixed atypical and cellular features), 2 aneurysmal, 1 atypical, and 1 epithelioid type. All tumors showed entrapment of hyalinized collagen bundles. Mitotic activity ranged from <1 to 13/10 HPF. Focal necrosis was seen in 1 primary tumor. Ten patients had local tumor recurrence; 4 patients had multiple local recurrences. Time to first recurrence ranged from 6 weeks to 13 years. The local recurrences of 1 tumor showed increased cytologic atypia, but recurrences were otherwise morphologically similar to primary tumors. Metastases occurred 0 to 180 months after diagnosis (median 17 mo) and involved the lungs (12 patients), lymph nodes (8), soft tissues (6), and liver (1). Five patients developed multiple satellite nodules in the region of the primary tumor. Metastases were morphologically similar to the primary tumors. So far, 6 patients died of disease, with a median time to death of 64 months (range, 10 to 168 mo). Four patients are alive with metastatic disease. Two patients are disease free at last follow-up, and 1 patient died of unrelated disease. Metastasis of morphologically benign cutaneous FH is an extremely rare but clinically aggressive event. Primary tumors tend to be large and cellular, but aggressive behavior cannot be predicted on morphologic grounds alone; however, early or frequent local recurrence may warrant closer clinical follow-up.

Malignant dermatofibroma: clinicopathological, immunohistochemical, and molecular analysis of seven cases

Dermatofibroma (cutaneous fibrous histiocytoma) represents a common benign mesenchymal tumor, and numerous morphological variants have been described. Some variants of dermatofibroma are characterized by an increased risk of local recurrences, and there are a few reported metastasizing cases. Unfortunately, an aggressive behavior cannot be predicted reliably by morphology at the moment, and we evaluated the value of array-comparative genomic hybridization (CGH) in this setting. Seven cases of clinically aggressive dermatofibromas were identified, and pathological and molecular features were evaluated. The neoplasms occurred in four female and in three male patients (mean age was 33 years, range 2-65 years), and arose on the shoulder, buttock, temple, lateral neck, thigh, ankle, and cheek. The size of the neoplasms ranged from 1 to 9 cm (mean: 3 cm). An infiltration of the subcutis was seen in five cases. Two neoplasms were completely excised, whereas an incomplete or marginal excision was reported in the remaining cases. Local recurrences were seen in six cases (time to the first recurrence ranged from 8 months to 9 years). Metastases were noted between 3 months and 8 years after diagnosis in six patients. Two patients died of disease, and two patients are alive with disease. Histologically, the primary tumors showed features of cellular dermatofibroma (four cases), cellular/aneurysmal dermatofibroma (one case), atypical/cellular dermatofibroma (one case), and classical dermatofibroma (one case). Mitotic figures ranged from 3 to 25 per 10 high-power fields, and focal necrosis was present in five cases. Interestingly, malignant transformation from cellular dermatofibroma to an obvious spindle cell/pleomorphic sarcoma was seen in one primary and in one recurrent neoplasm. Five neoplasms showed chromosomal aberrations by array-CGH, suggesting that these changes may represent an additional diagnostic tool in the recognition of cases of dermatofibroma with a metastatic potential.

Fibrohistiocytic tumors and related neoplasms in children and adolescents

Fibrohistiocytic tumors (FHTs) in children and adolescents range from the benign fibrous histiocytoma, or dermatofibroma, to a variety of intermediate and malignant neoplasms, such as dermatofibrosarcoma protruberans and high-grade undifferentiated pleomorphic sarcoma (malignant fibrous histiocytoma). Those tumors as a group are comprised of fibroblasts, myofibroblasts, and histiocytes-dendritic cells with a variably prominent inflammatory infiltrate consisting of lymphocytes and eosinophils. Dendritic cells are also a major constituent of another group of neoplasms that include Langerhans cell histiocytosis, follicular and interdigitating cell sarcomas, and juvenile xanthogranuloma. These latter tumors are considered in this discussion for the sake of differential diagnosis and their possible histogenetic relationship to FHTs. Recent studies have suggested that the relationship between the fibroblast and histiocyte in the FHTs may reflect the intrinsic capacity to transdifferentiate from one to the other morphologic and functional state. The so-called "facultative fibroblast," as a cell with fibroblastic and histiocytic properties, was discussed in the context of the fibrous xanthoma 50 years ago. Possibly the entire histogenetic concept of FHTs should be reconsidered in light of current studies.

Deep penetrating benign fibrous histiocytoma of the foot associated with throbbing pain

Compared to cutaneous benign fibrous histiocytoma (BFH), deep-seated BFH is very rare and poorly recognized. Both cutaneous and deep-seated BFH are usually asymptomatic. We herein report a 25 year-old woman who presented with a painful mass in her foot that was poorly controlled by analgesics and associated with walking difficulty. After preoperative ultrasonographic evaluation, the mass was completely excised and histologic exam showed spindle cells loosely arranged in storiform architecture, with CD34^-, desmin^-, S-100^-, focal CD68⁺, vimentin⁺, smooth muscle actin⁺, and factor XIIIa⁺. The patient was diagnosed with deep-seated BFH based on the histologic, radiologic and intraoperative findings.