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

Metastasizing aneurysmal dermatofibroma initially diagnosed as angiosarcoma confirmed by CD63::PRKCD fusion gene detection with nanopore sequencing

Dermatofibroma (DF) is a benign tumor that forms pedunculated lesions ranging in size from a few millimeters to 2 cm, usually affecting the extremities and trunks of young adults. Histopathologically, DF is characterized by the storiform proliferation of monomorphic fibroblast-like spindle cells. In addition to neoplastic cells, secondary elements such as foamy histiocytes, Touton-type giant cells, lymphoplasmacytes, and epidermal hyperplasia are characteristic histological features. Several histological variants, including atypical, cellular, aneurysmal, and lipidized variants, have been reported; cases with variant histologies are sometimes misdiagnosed as sarcomas. We present a case of metastasizing aneurysmal DF that was initially diagnosed as an angiosarcoma on biopsy. A 26-year-old woman was referred to our hospital with a gradually enlarging subcutaneous mass in her lower left leg. Positron emission tomography-computed tomography revealed high fluorodeoxyglucose uptake not only in the tumor but also in the left inguinal region. On biopsy, ERG and CD31-positive atypical spindle cells proliferated in slit-like spaces with extravasation, leading to the diagnosis of angiosarcoma. Histology of the wide-resection specimen was consistent with DF, and lymph node metastasis was also observed. Nanopore DNA sequencing detected CD63::PRKCD fusion and copy number gain, although CD63 was not included in the target region of adaptive sampling. This report highlights the importance of recognizing the unusual clinical, radiological, and pathological features of DF to avoid misdiagnosis, and the potential diagnostic utility of nanopore sequencer.

Recurrent and metastatic cellular cutaneous fibrous histiocytoma: A case report and literature review

Cutaneous fibrous histiocytoma (FH) is considered a benign dermal tumor. The cellular variant is rare and poorly documented. Besides presenting a high risk of local recurrence, it has a low but serious metastatic potential. We present a case of metastatic cellular FH and also review the literature on this tumor, given its unusual metastatic development. A 47-year-old male patient presented with a lesion in the anterior surface of the right thigh, which has been present since adolescence but had grown during last year. Anatomopathological evaluation revealed a cellular FH, and the lesion was completely removed. Six months later, tumor recurrence with multiple compartment muscle involvement and pulmonary metastasis were detected. Both lesions were completely resected and after 3 years of follow-up, the patient is asymptomatic and free of the disease. We conclude that FH should be carefully sampled to detect variants with high local recurrence rates or with some metastatic risk such as the cellular one. We recommend wide surgical resection and a close follow-up including chest x-rays or thorax computed tomography (CT) in all cellular FH cases with local recurrence.

Atypical fibrous histiocytomas and pleomorphic fibroma-type lesions in a patient with li-fraumeni syndrome

Atypical fibrous histiocytomas are an uncommon but benign variant of dermatofibroma where the neoplastic cells can feature cytological atypia constituted by prominent nuclear enlargement, pleomorphism and multinucleated giant cells. Though these can have a degree of atypia, they have a benign course and a failure to recognize these tumors as benign can lead to misdiagnosis and overtreatment, particularly in patients with Li-Fraumeni syndrome who are known to be predisposed to various malignancies. Here, we report a patient with atypical fibrous histiocytomas and multiple pleomorphic fibroma-type lesions in the setting of Li-Fraumeni syndrome.

Clinico-pathological and prognostic overview of metastasizing ameloblastoma: An overview of the systematic reviews

Background

Metastasizing Ameloblastoma (MA) is an aggressive variant of ameloblastoma (AM) with the ability to metastasize without cytological malignant changes. Thus it aims to comprehensively review the clinico-pathological and prognostic aspects of MA through integration of current literature.

Methods

Electronic searches were conducted in PubMed-MEDLINE, Scopus, Web of Science and Google Scholar. Two independent reviewers screened abstracts and evaluated paper eligibility. AMSTAR2 checklist was used to assessed methodological quality of included systematic reviews (SRs).

Results

From 390 initial papers, 279 underwent eligibility screening, with five systematic reviews (SRs) meeting inclusion criteria. Six hundred sixty-one MA cases were found in five SRs that were included. MA predominantly affects men, exhibits mandible preference, and occurs in individuals in their fourth or fifth decade. Benign metastatic deposits commonly manifest in lungs and lymph nodes. Distant metastasis probability rises with multiple recurrences and incomplete surgical removal. Tumor recurrence and metastasis unfavorably impact clinical outcomes. Quality of evidence assessment was absent across SRs; four SRs were critically low in methodological quality.

Conclusions

AM's metastatic potential lacks predictability. Early/multiple recurrences post-treatment may signal poor prognosis, warranting vigilant follow-up. Methodical analysis of each AM case is imperative to comprehend the metastatic-benign histology relationship.

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.

Pulmonary Metastasising Aneurysmal Fibrous Histiocytoma: A Case Report, Literature Review and Proposal of Standardised Diagnostic Criteria

An aneurysmal fibrous histiocytoma is a rare cutaneous soft-tissue tumour which accounts for approximately 0.06% of all dermatopathologies. Metastasis is exceedingly uncommon, to the point that there have only been eight reported cases in the scientific literature. We present the case of a 25-year-old male with a primary aneurysmal fibrous histiocytoma located in the nuchal region which exhibited rapid growth and abrupt ulceration over a short time span and showed signs of locoregional aggressive infiltration. A subsequent histopathological analysis confirmed the presence of diffuse solid and cystic pulmonary metastases. Further genetic sequencing verified LAMTOR1-PRKCD fusion. This case report seeks to review the existing literature on aneurysmal fibrous histiocytoma, discuss the challenges of differential diagnosis and propose standardised diagnostic criteria.

A rapidly enlarging nonpigmented nodule on the chest wall

We report a clinicopathological case of a patient with a rapidly enlarging nonpigmented nodule on the chest wall. There was no personal or family history of skin disease or cutaneous malignancy.

Challenging Patterns of Atypical Dermatofibromas and Promising Diagnostic Tools for Differential Diagnosis of Malignant Lesions

Dermatofibroma (DF) or fibrous histiocytoma is one of the most frequent benign cutaneous soft-tissue lesions, characterized by a post-inflammatory tissue reaction associated with fibrosis of the dermis. Clinically DFs have a polymorphous clinical aspect from the solitary, firm, single nodules to multiple papules with a relatively smooth surface. However, multiple atypical clinicopathological variants of DFs have been reported and, therefore, clinical recognition may become challenging, leading to a more burdensome identification and sometimes to misdiagnosis. Dermoscopy is considered an important tool in DFs diagnosis, as it improves diagnostic accuracy for clinically amelanotic nodules. Although typical dermoscopic patterns are most frequently seen in clinical practice, there have also been some atypical variants described, mimicking some underlying recurrent and sometimes harmful skin afflictions. Usually, no treatment is required, although an appropriate work-up may be necessary in specific cases, such as in the presence of atypical variants or a history of recent changes. This narrative review's aim is to summarize current evidence regarding clinical presentation, positive and differential diagnosis of atypical dermatofibromas and also to raise awareness about the importance of specific characteristics of atypical variants to better differentiate them from malignant conditions.

Diagnosis and differential diagnosis of dermatofibrosarcoma protuberans: Utility of high-resolution dynamic contrast-enhanced (DCE) MRI

BACKGROUND

Dermatofibrosarcoma protuberans (DFSP) is a kind of low-grade malignant spindle cell neoplasm, the diagnosis, and treatment, which have markedly attracted clinicians' attention for its repeated recurrence. High-resolution magnetic resonance imaging (HR-MRI) has shown unique capabilities in diagnosis of various cutaneous tumors.

MATERIALS AND METHODS

Data of 29 patients with clinically suspected DFSPs and undergoing dynamic contrast-enhanced (DCE) HR-MRI preoperatively were prospectively collected. The HR-MRI qualitative features were evaluated and compared. The DCE-associated quantitative parameters and the time-signal intensity curve (TIC) types were provided using DCE sequences.

RESULTS

A total of 7 DFSPs, nine dermatofibromas (DF, including four cases of cellular variant [CDF]), 12 keloids, and one nodular fasciitis were enrolled. DFSP showed the largest major diameter and the deepest depth. Five DFSPs (71.4%) showed ill-defined margins as well as infiltration of peripheral adipose. All DFSPs showed irregular shape. Most DFSPs presented hyperintensity on T₂ WI (71.4%) and iso-intensity on T₁ WI (85.7%). Six cases (85.7%) had significant enhancement, and six cases (85.7%) had homogeneous enhancement. There were significant differences of K^trans , K_ep , V_e and iAUC values among DFSPs, DFs, and keloids, and DFSP had the highest values for these parameters. Six DFSPs (85.7%) and four CDFs (100%) showed type-III TICs, while the other lesions showed type-Ⅰor type-Ⅱ TICs.

CONCLUSIONS

DCE-HR-MRI could show the growth characteristics of DFSPs, which was of great value for the diagnosis and differential diagnosis of DFSPs and was helpful for the determination of treatment options, thereby to improve the prognosis of patients.

Diagnostic utility of ERG immunostaining in dermatofibroma

AIMS

Dermatofibroma/fibrous histiocytoma (DF/FH) is a common cutaneous mesenchymal neoplasm exhibiting benign biological behaviour. However, the immunohistochemical utility of erythroblast transformation-specific-related gene (ERG) for diagnosing DF remains unknown. The authors reviewed the immunohistochemical status of ERG in different subtypes of DF and in its differential diagnoses.

METHODS

Overall, 97 cases of ordinary DF/FH, 6 cases of aneurysmal FH, 10 cases of cellular FH, 5 cases of angiomatoid FH, 2 cases of epithelioid FH, 64 cases of dermatofibrosarcoma protuberans (DFSP) and 52 cases of fibrous scar were retrieved. As the other histological types of cutaneous neoplasms, 6 cases of myxofibrosarcoma, 4 cases of undifferentiated pleomorphic sarcoma, 11 cases of atypical fibroxanthoma, 19 cases of malignant melanoma, 20 cases of nevocellular nevus, 20 cases of neurofibroma, 19 cases of schwannoma, 8 cases of angioleiomyoma and 1 case of pilar leiomyoma were included.

RESULTS

Immunohistochemical positivity for ERG was demonstrated in 87 of 97 cases (89.6%) of ordinary DF/FH, 7 of 10 cases (70%) of cellular FH, 3 of 6 cases (50%) of aneurysmal FH, 1 of 5 cases (20%) of angiomatoid FH and 1 of 52 cases (0.1%) of fibrous scar. All cases of DFSP, epithelioid FH and other types of cutaneous neoplasms included in the current investigation were negative for ERG. The intensity of ERG immunohistochemical staining in spindle-shaped cells appeared weaker than that in endothelial cells.

CONCLUSIONS

DF/FH was frequently positive for ERG immunostaining. ERG immunostaining may thus be useful to distinguish DF/FH from DFSP.

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.

Metastatic aneurysmal fibrous histiocytoma in a 20-year-old woman: A rare case report with review of the literature and discussion of its genomic features

Aneurysmal fibrous histiocytoma is an uncommon variant of cutaneous fibrous histiocytomas with a local recurrence rate of 19%. We present a case of aneurysmal fibrous histiocytoma in a 20-year-old female with a regional lymph node metastasis and subsequent satellite nodule. The patient initially presented with a 1-month history of two palpable nodules in left lower anterior shoulder and left axilla. Needle core biopsies from both lesions revealed an atypical spindle cell neoplasm with a differential diagnosis of aneurysmal fibrous histiocytoma and angiomatoid fibrous histiocytoma. The axillary dissection confirmed a metastatic deposit in 1 out of 22 lymph nodes. At 6 months a satellite nodule arose between the resection scar and the axilla histopathologically demonstrating a cellular spindle cell nodule at the dermis subcutaneous junction with large, blood-filled pseudovascular spaces lined by histiocytes. The periphery of the lesion showed collagen trapping without a lymphoplasmacytic infiltrate. The lesional cells were diffusely positive for CD10 and focally for CD68 and Illumina RNA fusion panel sequencing was negative. Herein we present this case of metastatic aneurysmal fibrous histiocytoma with review of the literature and discussion of biology, cytogenetic alterations, and differential diagnosis.

Prognostic evaluation of metastasizing ameloblastoma: A systematic review of reported cases in literature

Ameloblastoma is a benign odontogenic tumor which undergoes malignant transformation to ameloblastic carcinoma. However, rarely it metastasizes without undergoing cytological malignant changes, an entity referred to as Metastasizing Ameloblastoma (MA). Through this study, we aimed to review cases of MA reported since 2000 to explore the impact of clinico-demographic variables on its prognosis. Based on PRISMA guidelines, a review of relevant literature from PubMed/Medline, Science Direct and Cochrane database was performed from January 2000 to March 2019. A total of 65 cases were considered for further evaluation as per predefined inclusion and exclusion criteria. Results showed that lungs followed by lymph nodes were the most common sites for benign metastatic deposits. Multiple recurrences and inadequate surgical removal increase the probability of distant metastatic spread. Despite having benign cytological features, tumor recurrence and metastasis were associated with an unfavorable clinical outcome in MA.

Fibrous histiocytoma/dermatofibroma in children: the same as adults?

Fibrous histiocytoma (FH) or dermatofibroma is a common cutaneous lesion mostly seen in adults and rare in the first two years of life. Two hundred sixty-seven patients younger than 18 years with a diagnosis of FH or dermatomyofibroma, a lesion with morphologic overlap with FH, were identified from the files of a single institution, with only 13 (4.8%) occurring in patients younger than 5 years. Ten patients had either underlying neurologic, autoimmune, or metabolic disorders or a family history of autoimmune conditions. Histologic review of hematoxylin and eosin staining and immunostaining on 75 FHs and dermatomyofibroma in 70 patients showed the following results: 33 classic FHs, 8 classic FHs characterized by a peculiar retiform morphology with thin fascicles of elongated cells forming a network reminiscent of the eruptive variant of FH, 19 deep/cellular variants, 5 aneurysmal variants, 3 lipidized variants (including two lesions in a patient affected by mucopolysaccharidosis IV), 3 dermatomyofibromas, and 4 isolated cases of hemosiderotic, granular cell atypical, and epithelioid FH. Immunostaining for factor XIIIa highlighted a dense network of dendritic cells in FH, which was significantly reduced in the FH with retiform morphology. Smooth muscle actin staining was positive in a high percentage of FHs (85.3%). The current series demonstrates that FH in children may show unique clinical and morphologic features. The retiform pattern with decreased dendritic cells found in congenital lesions and in two older patients with lesions in two locations might have a different pathogenesis, probably related to an altered immune response in very young patients.

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.

A retrospective review of 93 cases of cellular dermatofibromas

BACKGROUND

Cellular dermatofibromas (CDF) are an uncommon variant of benign fibrous histiocytomas with propensity to recur and rarely metastasize as well as demonstrate histologic similarities to more dangerous lesions.

OBJECTIVES

The aim of this present study was to further describe the presentation and outcome of the cellular variant of benign fibrous histiocytomas so that it can be diagnosed and treated appropriately.

METHODS

A retrospective chart review was performed on all patients seen in a single hospital system in Detroit, Michigan, from 2007 to 2017. CDF was confirmed by pathology. Baseline demographics, specialty service of diagnosis and treatment, treatment modality, and outcome were collected.

RESULTS

Of the 93 qualifying patients, the average age at diagnosis was 42.65 years. The most common specialty service that diagnosed and treated patients was dermatology (38.71%). About 95.0% of CDF stained positive for Factor 13A (19/20), and 90.48% were CD34 negative (19/21). Of patients, 33.33% had recurrences of their CDF (9/27). Two patients had three or more recurrences. One patient's death was attributed to the CDF.

CONCLUSION

CDF have a high local recurrence rate and similarities to more dangerous and malignant lesions. Patients with cellular dermatofibromas present to many subspecialty services for diagnosis and should be treated aggressively.

Giant Muscle Invasive Dermatofibroma Clinically Mimicking a Malignant Tumor

Dermatofibromas are common benign fibrohistiocytic lesions, usually appearing as slow growing firm dermal nodules with a predilection for the extremities (mostly the lower legs). They are found mostly in middle-aged women and are usually smaller than 2 cm in diameter. Giant dermatofibromas exceeding 5 cm in diameter are rare. In recent years, reports have suggested a relationship between the primary size of dermatofibromas and rates of local recurrence and metastases after surgery. This relationship is however debated. The present report describes the case of a giant muscle invasive tumor in a 51-year-old female patient who presented with a large ulcerated mass in the right upper arm. The tumor appeared clinically malignant, measuring approximately 12 cm × 6 cm in size, with ulceration and invasion of surrounding muscle. Wide resection of the tumor was performed with myocutaneous flap-plasty. Histopathological examination showed evidence of a dermatofibroma. No recurrence, metastases, or other complications were noted at 5 years after surgery. The present case demonstrates that although dermatofibromas are essentially benign, they may present with atypical features including large size, ulceration, and muscle invasion, clinically mimicking malignant tumors.

Aneurysmal fibrous histiocytoma

Aneurysmal fibrous histiocytoma (AFH) is a type of fibrohistiocytic tumour. We present a case of a patient who presented with a skin papule on the thigh region. Histopathological examination following total excision of the lesion revealed an AFH. No sign of recurrence was present 6 months after surgery.

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.

Giant aneurysmal benign fibrous histiocytoma (dermatofibroma)

Aneurysmal benign fibrous histiocytomas are variants of dermatofibromas. These benign blood-filled lesions can mimic malignancies due to their rapid and recurrent growth. Our patient is a 42-year-old Caucasian female with a past medical history of morbid obesity, diabetes, and hypertension, who presented with a mass on her left shoulder for 5 years' duration. The mass oozed occasionally and would appear to regress but then recur replaced with progressively larger masses. Upon inspection, the patient had a large pedunculated exophytic mass with vascularity. The mass was surgically removed under general anesthesia via wide local excision. Grossly, the excised skin was purple-tinged with an underlying fungating solid mass measuring 8.5 cm. Serial sections revealed a hemorrhagic, spongy, and granular cut surface. Histologically, the epidermis was hyperplastic, with underlying hyaline collagen bundles. The remainder of the mass was chronically inflamed and composed of spindled histiocytes, hemosiderin-laden macrophages, and blood-filled spaces lacking an endothelial lining. There was focal pleomorphism but no significant atypia. Immunohistochemical stains were strongly positive for vimentin and negative for CD31, CD34, and desmin. The overall architecture and immunophenotype are consistent with the diagnosis of aneurysmal benign fibrous histiocytoma.

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.

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.

Advances in the Genetic Characterization of Cutaneous Mesenchymal Neoplasms: Implications for Tumor Classification and Novel Diagnostic Markers

Cutaneous mesenchymal neoplasms often pose significant diagnostic challenges; many such entities are rare or show clinical and histologic overlap with both other mesenchymal and non-mesenchymal lesions. Recent advances in the genetic classification of many cutaneous mesenchymal neoplasms have not only helped define unique pathologic entities and increase our understanding of their biology, but have also provided new diagnostic markers. This review details these recent discoveries, with a focus on their implications for tumor classification and diagnosis.

Conjunctival fibrous histiocytoma in an 8-year-old boy

An 8-year-old healthy boy underwent surgery for excision of a painless, enlarging vascularized conjunctival tumor. Histopathology disclosed a mass comprised of interweaving spindle cells and scattered histiocytes in a fibrous matrix, consistent with benign fibrous histiocytoma. This rare tumor can resemble several conditions, including scleritis/episcleritis, inflamed pterygium, juvenile xanthogranuloma, foreign body granuloma, solitary fibrous tumor, amelanotic melanoma, and squamous cell carcinoma.

A primary cellular fibrohistiocytoma of the lung: Report of a case

•

We experienced a rare patient with a primary cellular fibrohistiocytoma (CFH).

•

Our search of literature only revealed one case of a primary CFH of the lung.

•

It is essential to perform resection with an adequate margin with close clinical follow-up.

Introduction

Cellular fibrohistiocytoma (CFH) is a type of fibrohistiocytic tumor that commonly occurs in the dermis and superficial subcutis. The designation is used for lesions that show increased cellularity with a fascicular growth pattern and frequent extension. Our search of literature only revealed one case of a primary CFH of the lung. We experienced a rare patient with a primary CFH of the lung.

Presentation of case

We herein present a rare case of a 77-year-old female patient without a cutaneous lesion, who underwent resection for what was considered to be a primary CFH of the lung. There has been no recurrence including a cutaneous lesion in a year after surgery.

Discussion

CFH is considered to be benign, but rare cases showing multiple recurrences and involving metastasis to the lymph nodes and internal organs have been reported. At present, it is not possible to predict this aggressive biological behavior based on the tumor histology.

Conclusion

It is essential to perform resection with an adequate margin with close clinical follow-up.

Advances in the clinicopathological and molecular classification of cutaneous mesenchymal neoplasms

In recent years, there have been several important refinements in the classification of cutaneous mesenchymal neoplasms, including the description of new tumour types, along with the identification of novel and recurrent molecular genetic findings. In addition to providing new insights into tumour biology, many of these advances have had significant clinical consequences with regard to diagnostics, management, and prognostication. Newly described entities include pseudomyogenic haemangioendothelioma, haemosiderotic fibrolipomatous tumour, and fibroblastic connective tissue naevus, which are reviewed in the context of the principal differential diagnoses and significant clinical implications. Genetic characterization of several soft tissue tumour types that occur in the skin has resulted in the identification of diagnostically useful markers: ALK gene rearrangement with corresponding ALK protein expression by immunohistochemistry in epithelioid fibrous histiocytoma; the WWTR1-CAMTA1 fusion gene with CAMTA1 protein expression in epithelioid haemangioendothelioma; MYC amplification and overexpression in radiation-associated angiosarcoma; and EWSR1 gene rearrangement in cutaneous myoepithelial tumours. Finally, the classification of intradermal smooth muscle tumours and unclassified/pleomorphic dermal sarcoma has been refined, resulting in both improved classification and improved prognostication. Many of the tumour types listed above are encountered not only by specialist dermatopathologists, but also by practising general surgical pathologists, and this review should therefore provide a widely applicable update on the histological and molecular classification of cutaneous mesenchymal neoplasms, along with the appropriate use of ancillary diagnostic tests, in particular immunohistochemistry, in the evaluation of such lesions and their histological mimics.

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.

ALK rearrangement and overexpression in epithelioid fibrous histiocytoma

Epithelioid benign fibrous histiocytoma, also known as 'epithelioid cell histiocytoma,' has traditionally been considered a morphologic variant of cutaneous fibrous histiocytoma (dermatofibroma). In addition to its characteristic epithelioid cytomorphology, several phenotypic differences suggest that epithelioid fibrous histiocytoma may differ biologically from other variants. Recently, ALK rearrangement was described in two cases of epithelioid fibrous histiocytoma and separately in two cases reported as 'atypical' fibrous histiocytoma (with epithelioid features), with corresponding ALK expression detectable by immunohistochemistry. The goals of this study were to determine the frequency of ALK expression by immunohistochemistry in epithelioid fibrous histiocytoma, to determine its value for the diagnosis of epithelioid fibrous histiocytoma among variants and other histologic mimics, and to evaluate ALK gene rearrangement in epithelioid fibrous histiocytoma. ALK protein expression was evaluated in whole tissue sections from 33 epithelioid fibrous histiocytomas, 41 other cases of fibrous histiocytoma (11 conventional and 10 each cellular, atypical, and aneurysmal types), 10 cutaneous syncytial myoepitheliomas, and 5 atypical fibroxanthomas, using a mouse anti-ALK monoclonal antibody. Fluorescence in situ hybridization (FISH) was performed using break-apart probes. In total, 29/33 (88%) cases of epithelioid fibrous histiocytoma showed diffuse cytoplasmic ALK expression. Staining was moderate to strong in intensity in all cases except one, which showed diffuse weak expression. All other tumor types were negative for ALK expression. FISH demonstrated ALK rearrangement in all ALK-immunoreactive cases evaluated (n=13), and not in one ALK expression-negative epithelioid fibrous histiocytoma successfully examined. In conclusion, the majority of epithelioid fibrous histiocytomas demonstrate ALK expression and ALK gene rearrangement. ALK expression is not seen in other variants of fibrous histiocytoma, providing a useful diagnostic tool to distinguish epithelioid fibrous histiocytoma from most histologic mimics. The expression of ALK suggests that epithelioid fibrous histiocytoma is a biologically distinct tumor type, unrelated to conventional fibrous histiocytoma and histologic variants.

A Case of Cellular Fibrous Histiocytoma on the Right Elbow with Repeated Relapse within a Short Period

Cellular fibrous histiocytoma, a variant of fibrous histiocytoma, is a designation used for lesions showing increased cellularity with a fascicular growth pattern and frequent extension into the subcutis. Here we describe a case of cellular fibrous histiocytoma showing repeated recurrence in a 36-year-old woman who initially presented with a 2-cm cutaneous tumor on her right elbow. Histopathologically, the first resected specimen demonstrated irregularly arranged collagen fibers mixed with scattered proliferating plump to spindle-shaped fibrohistiocytes. However, examination of the resected specimens obtained after recurrence showed that the cellularity had increased, the spindle-shaped cells showing monomorphic proliferation with a fascicular and storiform growth pattern extending into the subcutis, as well as an increase of Ki-67 positivity. Since the lesion showed repeated relapse within a short period, we performed wide-field resection of the tumor with a 3-cm margin. Currently, 48 months after surgery, there has been no local recurrence or metastasis, but continuous strict follow-up will be necessary.

[Fibrohistiocytic tumors of the skin: a heterogeneous group of superficially located mesenchymal neoplasms]

So-called fibrohistiocytic tumors of the skin comprise a heterogeneous spectrum of superficially located neoplasms that often show fibroblastic and/or myofibroblastic differentiation. In this review clinicopathologically important variants of dermatofibroma and dermatofibrosarcoma protuberans and their differential diagnoses are discussed in detail. In addition, the clinicopathological features of atypical fibroxanthoma, angiomatoid fibrous histiocytoma, plexiform fibrohistiocytic tumors and pleomorphic dermal sarcoma are presented. Entities that have to be considered in the differential diagnosis are also mentioned.

Shouldn't we care about the biology of benign tumours?

While focusing on malignant tumours seems medically reasonable, from a biological perspective, benign and malignant tumours provide complementary and perhaps equally relevant perspectives on the mechanisms of tumour invasion and metastasis. However, the biology of benign neoplasms is rarely studied.

Fusions involving protein kinase C and membrane-associated proteins in benign fibrous histiocytoma

Benign fibrous histiocytoma (BFH) is a mesenchymal tumor that most often occurs in the skin (so-called dermatofibroma), but may also appear in soft tissues (so-called deep BFH) and in the skeleton (so-called non-ossifying fibroma). The origin of BFH is unknown, and it has been questioned whether it is a true neoplasm. Chromosome banding, fluorescence in situ hybridization, single nucleotide polymorphism arrays, RNA sequencing, RT-PCR and quantitative real-time PCR were used to search for recurrent somatic mutations in a series of BFH. BFHs were found to harbor recurrent fusions of genes encoding membrane-associated proteins (podoplanin, CD63 and LAMTOR1) with genes encoding protein kinase C (PKC) isoforms PRKCB and PRKCD. PKCs are serine-threonine kinases that through their many phosphorylation targets are implicated in a variety of cellular processes, as well as tumor development. When inactive, the amino-terminal, regulatory domain of PKCs suppresses the activity of their catalytic domain. Upon activation, which requires several steps, they typically translocate to cell membranes, where they interact with different signaling pathways. The detected PDPN-PRKCB, CD63-PRKCD and LAMTOR1-PRKCD gene fusions are all predicted to result in chimeric proteins consisting of the membrane-binding part of PDPN, CD63 or LAMTOR1 and the entire catalytic domain of the PKC. This novel pathogenetic mechanism should result in constitutive kinase activity at an ectopic location. The results show that BFH indeed is a true neoplasm, and that distorted PKC activity is essential for tumorigenesis. The findings also provide means to differentiate BFH from other skin and soft tissue tumors. This article is part of a Directed Issue entitled: Rare cancers.