Atypical fibrous histiocytoma of the skin: clinicopathologic analysis of 59 cases with evidence of infrequent metastasis

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.

Undifferentiated Pleomorphic Sarcoma with Reactive Eccrine Syringofibroadenoma: A Case Report

Undifferentiated pleomorphic sarcoma (UPS) is an aggressive soft tissue sarcoma with a poor prognosis. The patients are usually found to have metastasis when the primary tumor is diagnosed. Eccrine syringofibroadenoma (ESFA) is a rare cutaneous adnexal lesion of eccrine duct origin. There are five subtypes, one of which is reactive ESFA, known to occur in reaction to an inflammatory or neoplastic process. In this article, we report a case of the co-existence of both UPS and ESFA in a 70-year-old male patient, presenting with a painless, erythematous, irregular surface nodule with a peripherally extended brownish hyperkeratotic plaque on the right palm. The histologic findings revealed an ill-defined dermal tumor of atypical epithelioid and spindle-shaped cells with large pleomorphic hyperchromatic nuclei and abundant eosinophilic cytoplasm. Some of those cells were multinucleated giant cells in the stroma with vascular proliferation and mixed inflammatory cell infiltrate. The tumor cells, which were only positive for vimentin, supported the diagnosis of undifferentiated pleomorphic sarcoma (UPS). Meanwhile, the overlying epidermis demonstrated hyperkeratosis, papillated epidermal hyperplasia, and proliferation of anastomosing slender cords and strands of cuboid cells within loose fibrovascular stroma. These findings are the characteristics of eccrine syringofibroadenoma (ESFA). We describe here a patient in whom reactive ESFA occurred on and surrounded the UPS tumor.

Superficial CD34+ fibroblastic tumor with focal atypical presentation: A case report

Superficial CD34+ fibroblastic tumors (SCPFTs) are rare mesenchymal tumors with distinct morphological features. Although several cases of SCPFT have been reported, a comprehensive understanding of its clinical and biological features necessitates the inclusion of additional cases. The current study presents a case of SCPFT, where morphological observations, immunohistochemical staining and fluorescence in situ hybridization (FISH) were performed. Immunohistochemistry revealed diffuse CD34 expression and integrase interactor 1 expression, whilst FISH indicated rearrangement of the PR/SET domain 10 gene. Microscopic assessment demonstrated typical SCPFT pathology, with a focal nodular region showing a high Ki-67 index, suggesting heterogeneity and the potential for local recurrence. The present study also briefly reviews the differential diagnosis of tumors with morphological similarities. It was found that the precise diagnosis of SCPFT relies on the distinctive pathological features, the use of immunohistochemical markers, including CD34 staining, and the differentiation from similar histological lesions.

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.

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.

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.

ETS-related Gene (ERG) is Differentially Expressed in Dermatofibroma (Fibrous Histiocytoma) as Compared With Dermatofibrosarcoma Protuberans and Hypertrophic Scars: A Pilot Immunohistochemical Study

Immunohistochemical staining can be of great utility in differentiating various cutaneous spindle cell neoplasms, particularly when the histomorphologic appearance of the lesions is inconclusive. Nuclear staining for ETS-related gene (ERG), a highly sensitive endothelial cell marker, has seldom been studied in the context of cutaneous spindle cell neoplasms. Little is known about its specificity for vascular differentiation. In this pilot study, immunohistochemical analysis for ERG was performed on 15 dermatofibromas (DF), 10 keloids, and 9 dermatofibrosarcoma protuberans (DFSP) tumors. Consistent nuclear expression of ERG was found in DF [100% (15/15) of the lesions demonstrated >50% labeling of tumor cells with moderate to strong intensity]. However, ERG expression was largely absent in DFSP [89% (8/9) of the lesions demonstrating <50% labeling staining, generally of mild intensity] and hypertrophic scars-keloids [80% (8/10) without expression]. On the basis of the results of this pilot study, immunohistochemical staining for ERG may prove useful in helping to differentiate DF from DFSP and hypertrophic scars in the context of partial biopsy sampling. If replicated in a larger number of samples, this finding could mitigate the use of costly sequencing panels and potentially avoid unnecessary reexcisions in certain contexts.

Hemosiderotic dermatofibroma mimicking melanoma: A case report and review of the literature

Hemosiderotic dermatofibroma (HDF) often mimics melanoma clinically. A definite diagnosis relies on histopathological evaluation and immunohistochemistry. As it can progress to aneurysmal dermatofibroma (ADF), complete excision is recommended.

Angiosarcomas: histology, immunohistochemistry and molecular insights with implications for differential diagnosis

Angiosarcomas (AS) represent a heterogenous group of tumors with variable clinical presentation. AS share an important morphologic and immunohistochemical overlap with other sarcomas, hence the differential diagnosis is challenging, especially in poorly-differentiated tumors. Although molecular studies provide significant clues, especially in the differential diagnosis with other vascular neoplasms, a thorough hematoxylin and eosin analysis remains an essential tool in AS diagnosis. In this review, we discuss pathological and molecular insights with emphasis on implications for differential diagnosis in cutaneous, breast, soft tissue and visceral AS.

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.

Atypical fibroxanthoma: An analysis of 105 tumors

Atypical fibroxanthoma (AFX) is a rare, low-grade dermal sarcoma. We analyzed our files from January 2001 to January 2020 for AFX. Clinical parameters, histopathology, treatment and outcome have been investigated. We identified 87 patients (mean age of 80.0 ± 8.4 years) with 105 confirmed tumors. Of these patients 86.2% were males. The most common clinical presentation was nodular (93.3%). The majority of AFX was located on the head with a mean tumor diameter of 15.0 mm ± 3.5 mm. All tumors showed a dermal localization, in 46.4% with a focal infiltration of the deeper layers. Second skin cancer was reported in 62.1% of patients. Collision tumors were seen in six patients. Treatment was surgical with three-dimensional margin control. Relapses were noted in 11.4% of tumors with a mean delay of 11.7 ± 17.3 months. Focally deeper infiltration of AFX was a risk factor (P = .014). None of the purely dermal AFX relapsed. No metastasis was observed. AFX is a rare mesenchymal tumor of elderly patients. Treatment of choice is the complete surgical excision. Due to the high rate of other skin malignancies among patients with AFX, a regular follow-up is recommended.

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.

Cellular Dermatofibroma: Clinicopathologic Review of 218 Cases of Cellular Dermatofibroma to Determine the Clinical Recurrence Rate

BACKGROUND

Cellular dermatofibromas, a variant of dermatofibroma, are reported to recur at rates of 26% to 50%.

OBJECTIVE

To determine whether there are distinct clinical or histological differences between cellular dermatofibromas that recur versus those that do not. To determine recurrence rates in a real-world clinical setting.

MATERIALS AND METHODS

A retrospective analysis of the medical records and skin biopsies of cellular dermatofibroma in the University of Utah Health system between December 2011 and 2016. Clinical and dermatopathological features were evaluated to find distinct differences between the cellular dermatofibromas that recurred compared with those that did not.

RESULTS

There were no significant differences in histology between the primary lesions in recurrent and nonrecurrent cases. One factor that seemed to be associated with a greater likelihood of recurrence was an initial lesion size greater than 1 cm. The authors' data suggest that if the margins are involved on initial biopsy, there is a 10% chance of recurrence. This percentage is far less than the 26% to 50% reported in the past literature.

CONCLUSION

If a patient presents with a cellular dermatofibroma larger than 1 cm and positive margins at initial biopsy, a careful discussion should be had between the provider and patient about the low risk of local recurrence.

Cutaneous soft tissue tumors: how do we make sense of fibrous and "fibrohistiocytic" tumors with confusing names and similar appearances?

In the 2018 World Health Organization Classification of Skin Tumors, a wide range of predominantly benign mesenchymal neoplasms are included in the fibroblastic, myofibroblastic, and "fibrohistiocytic" categories. By far the most common of these tumors is dermatofibroma (fibrous histiocytoma). There are many histologic variants of dermatofibroma, some of which (cellular, aneurysmal, and atypical) are associated with a higher risk of local recurrence; these variants may be mistaken for more aggressive tumor types, including sarcomas. Furthermore, distinguishing among the fibrous and "fibrohistiocytic" tumors can be a diagnostic challenge, given their sometimes-similar histologic appearances and confusing nomenclature. Immunohistochemistry and molecular genetic assays play a relatively limited role in the diagnosis of these tumor types, with notable exceptions (i.e., epithelioid fibrous histiocytoma and dermatofibrosarcoma protuberans). Proper recognition of dermatofibrosarcoma protuberans is critical, since this tumor type is associated with locally aggressive behavior; transformation to the fibrosarcomatous variant brings metastatic potential. In recent years, understanding of the molecular pathogenetic basis for cutaneous mesenchymal neoplasms has increased dramatically, with the discovery of gene rearrangements in some of these tumor types. In this review, the histologic features of the most common fibrous and "fibrohistiocytic" cutaneous mesenchymal neoplasms will be discussed, as well as recently identified molecular genetic alterations.

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.

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.

Phosphohistone-H3 and Ki67: Useful Markers in Differentiating Dermatofibroma From Dermatofibrosarcoma Protuberans and Atypical Fibrohistiocytic Lesions

Dermatofibromas (DF) are common, benign, skin tumors, usually easily differentiated from dermatofibrosarcoma protuberans (DFSP) by the presence of a relative low cellularity, lesser degree of infiltration of subcutaneous tissue, and immunohistochemical pattern (eg, FXIIIa in DF and CD34 in DFSP). Atypical fibrohistiocytic lesions (AFL) have features intermediate to DF and DFSP (trunk location, storiform pattern, infiltration of the subcutaneous tissue, and focal expression of both CD34 and Factor XIIIa). It is unclear if mitotic counts/degree of proliferation is helpful to distinguish DF from DFSP. To study the mitotic rate and proliferation index in DF, AFL/DFSP, anti-ki67, and anti-PHH3 were performed on 10 cases of DF (including 4 cellular DF), 10 standard DFSP, and 2 AFL. The proliferation index and mitotic figures were counted per square millimeter in a "hotspot" (in a fashion similar to mitotic counts in melanoma). All cases of DF showed much higher Ki67 proliferation index (P = 0.0001) along with increased mitotic figures both on H&E and with anti-PHH3 (P = 0.0001) when compared to AFL/DFSP. Our data indicate that DF has a higher proliferation index and mitotic counts when compared to superficial/peripheral portion of AFL and DFSP. This finding may be helpful in the differential diagnosis among these fibrohistiocytic lesions.

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.

Cutaneous and Superficial Soft Tissue CD34+ Spindle Cell Proliferation

CONTEXT

- Cutaneous and superficial soft tissue spindle cell proliferations with CD34 expression represent a unique heterogeneous group of lesions. They can pose diagnostic challenges for unaware pathologists in their daily practice.

OBJECTIVE

- To review selected entities of CD34⁺ spindle cell proliferations in the skin and superficial soft tissue. The effective diagnostic approaches using clinical, histopathologic, and immunophenotypical findings are discussed within a broad spectrum of differential diagnosis.

DATA SOURCES

- All information used in the article is obtained from published literature by PubMed search and Internet-based search engines. The authors' collective experience and real-life examples are also used.

CONCLUSIONS

- Spindle cell proliferations with CD34 positivity can be worked up to a definitive diagnosis by using clinical, histopathologic, and immunophenotypical findings. Familiarity with these entities helps pathologists make the accurate diagnosis.

Superficial CD34-positive fibroblastic tumour: a clinicopathological and immunohistochemical study of an additional series

AIMS

To describe an additional series of superficial CD34-positive fibroblastic tumour, a newly described neoplasm, in order to enhance the recognition of an emerging novel entity.

METHODS AND RESULTS

The clinicopathological features and immunophenotypes of 11 cases of superficial CD34-positive fibroblastic tumour were studied. There were eight males and three females, with a median age of 36 years. Tumours occurred in the thigh (n = 4), buttock (n = 3), shoulder (n = 2), upper arm (n = 1), and waist (n = 1). Histologically, all tumours were characterized by relative circumscription, pleomorphic spindled to polygonal cells with variably enlarged bizarre-appearing cells, intranuclear cytoplasmic pseudoinclusions, and extremely low mitotic activity. Immunohistochemically, neoplastic cells showed diffuse and strong expression of CD34 and focal staining of cytokeratin. Follow-up thus far has revealed an indolent clinical behaviour.

CONCLUSIONS

Superficial CD34-positive fibroblastic tumour represents a new member of the family of cutaneous CD34-positive spindle-cell tumours. Familiarity with its clinicopathological characteristics is helpful in avoiding confusion with a variety of cutaneous mesenchymal tumours with overlapping features.

Keloidal Atypical Fibroxanthoma: Case and Review of the Literature

Keloidal atypical fibroxanthoma (KAF) has recently been categorized as a variant of atypical fibroxanthoma. This paper will emphasize the importance of including KAF in both clinical and histological differential diagnosis of benign and malignant lesions which exhibit keloidal collagen and will also review the current literature on epidemiology, pathogenesis, histology, immunochemistry and treatments.

Superficial CD34-positive fibroblastic tumor: A new case from Japan

A 48-year-old Japanese woman presented with a painless, slow-growing, brown nodule of 15 mm in diameter on the left thigh. She noticed the nodule a few years before the first presentation to our hospital. She underwent total resection of the nodule. On histopathological examination, a relatively well-defined tumor with infiltrative growth was located in the dermis and extended into the subcutis. The tumor was composed of spindle to polygonal cells with pleomorphic nuclei arranged in a sheet-like or fascicular pattern. Tumor cells with granular cytoplasm were also scattered. Immunohistochemical examination revealed that the tumor cells were strongly positive for CD34. The fusion transcripts of the collagen type 1 alpha 1 platelet-derived growth factor beta chain were not detected. After excluding other fibroblastic tumors through histopathological and immunohistochemical examinations, a diagnosis of superficial CD34-positive fibroblastic tumor (SCPFT) was made. SCPFT is a recently proposed fibroblastic tumor that is characterized by striking pleomorphism, granular cytoplasm, low mitotic rate and diffuse CD34 expression. Only two reports with 20 cases have been reported so far. The present case is the first that corresponds to SCPFT in Japan.

Pleomorphic dermal sarcoma: a more aggressive neoplasm than previously estimated

BACKGROUND

Pleomorphic dermal sarcoma (PDS) is a rare neoplasm sharing pathological features with atypical fibroxanthoma, but adding tumor necrosis, invasion beyond superficial subcutis or vascular or perineural infiltration. Although its metastatic risk has been estimated to be less than 5%, its real outcome is presently uncertain because of its rarity and to the lack of homogeneous criteria used in reported cases.

METHODS

Retrospective clinicopathological study of 18 cases of PDS.

RESULTS

The lesions presented as tumors or plaques (size: 7-70 mm) on the head of elderly patients (median: 81 years), without a gender predominance. Histopathologically, they consisted of spindle cells arranged in a fascicular pattern, containing pleomorphic epithelioid and giant multinucleated cells in varying proportions, and usually exhibiting numerous mitotic figures and infiltrative tumor margins. No immunoexpression for cytokeratins, S100 protein, desmin or CD34 was observed. Necrosis and venous invasion were found in three tumors each (17%). Follow-up was available in 15 cases (median: 33 months). Three patients (20%) had local recurrences, all with incomplete primary surgical resections. Three patients (20%) developed distant metastases in the skin, regional lymph nodes and/or lungs and died from the disease.

CONCLUSION

Our data suggest that PDS may be a more aggressive neoplasm than previously estimated.

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.

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.

Sarcoma-like tumor of head and neck skin

A group of tumors referred to as atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS) predominantly occur in sun-damaged skin of the elderly, particularly in the head and neck region. Although this group of tumors is often regarded as of mesenchymal phenotype, the matter of histogenesis has not been entirely resolved. Evans H and Smith JL reported in 1980 that prognosis was not significantly different irrespective of whether there was a definite squamous cell carcinoma component or not, supporting a view that these are all carcinomata in nature (sarcomatoid carcinoma [SC]). There are a number of clinicopathologic studies of AFX in the literature but information on morphologically similar sarcoma-like tumors with immunohistochemical evidence of epithelial differentiation is sparse. One hundred sarcoma-like tumors (SLTs) of head and neck skin of the elderly, treated by surgical excision, were studied. Clinical information was obtained, and pathology reports and hematoxylin and eosin sections were reviewed to document size (maximum dimension), extent of invasion, mitotic count, vascular and perineural invasion, margin status, ulceration, necrosis, and the presence of actinic keratosis in adjacent/overlying skin. Immunostains examined included: pan-cytokeratins (CKs) (AE1/AE3, MNF116), high-molecular weight CKs (34βE12, CK5/6, CK14), p63, and melanocytic (S100, Melan A, HMB-45, MITF), vascular (CD31, CD34), and muscle markers (SMA, desmin, h-caldesmon) to exclude melanoma and definite sarcoma entities. The tumors were divided into AFX/PDS (G1), the SC group, which was subdivided into SLT with only p63 positivity (G2a) and SLT with CK positivity regardless of p63 status (G2b), and SLT with a minor morphologic squamous cell carcinoma component (G3). Clinicopathologic findings of each group were compared, in relation to outcomes. Age at diagnosis ranged from 51 to 96 years (median, 79 y), with M:F=11.5:1. There were 53 tumors in G1 (19AFX, 34PDS), 37 in G2 (25 in G2a, 12 in G2b), and 10 in G3. There was no statistically significant difference in clinical and pathologic parameters or survival among all 3 groups. CKs and p63 expression, size, extent of invasion, vascular invasion, perineural invasion, mitotic count, and ulcer did not affect outcome, whereas margin status and necrosis did by both univariate and multivariate analysis and by only univariate analysis, respectively. Sixty patients had multiple nonmelanomatous skin cancers. Actinic keratosis was observed in overlying/adjacent epidermis in 51 cases. Eight patients had prior radiotherapy to head skin cancers; 1 patient developed 2 separate tumors (G1 and G3) after radiotherapy. Four patients died of tumor (1 G1, 2 G2b, and 1 G3); of these, 3 cases had positive margin, and 1 had narrow margin. Our results have shown similarities of various clinicopathologic parameters between AFX/PDS and SC, raising the possibility that both entities are related, and some of the former entities may represent complete dedifferentiation (complete loss of epithelial phenotype) with a gain of mesenchymal phenotype. In addition, the difference between AFX and PDS appears to be the extent of invasiveness (stage) rather than a different histogenesis. Further investigations are needed. However, from a practical point of view, efforts should be made to excise this group of tumors with clear margins, as margin status appears to be the most important prognostic factor regardless of the presence or absence of epithelial differentiation.

Atypical fibrous histiocytoma of the skin with CD30 and p80/ALK1 positivity and ALK gene rearrangement

We report the case of a two patients who presented with a solitary, asymptomatic, angiomatoid nodule on the right thigh. Histopathological finding showed a poorly circumscribed lesion, located in the dermis. The morphological aspect strongly suggested the diagnosis of atypical fibrous histiocytoma (AFH), but surprisingly, the neoplastic cells were diffusely CD30+, with a membrane staining devoid of paranuclear dot. The lesions were tested for p80/ALK1 expression. Surprisingly, we found a diffuse cytoplasmic positivity. Interestingly, using break-apart fluorescent in situ hybridization (FISH), we evidenced an ALK rearrangement in nearly 50% of the neoplastic cells. The expression of CD30 and ALK1 with ALK gene rearrangement raised the possibility of three diagnoses: a primary cutaneous anaplastic large cell lymphoma (ALCL), a cutaneous inflammatory myofibroblastic tumor (IMT), an AFH of the skin associated with ALK gene rearrangement and CD30 positivity. The three hypotheses were discussed and finally, although p80/ALK1 expression and cytogenetic abnormalities in fibrous histiocytoma (FH) are not yet reported to the best of our knowledge, we favored the diagnosis of AFH.

[Atypical histiocytoma in a child]

BACKGROUND

Histiocytoma (HC) is a very common benign tumour generally seen in the lower limbs of adults, particularly women. There are, however, atypical forms of HC that behave like locally aggressive tumours, occasionally with relapse or even metastasis. Herein we report a case of locally aggressive HC in a child, which, on account of its clinical extension, required seven surgical procedures to achieve complete excision.

PATIENTS AND METHODS

A 13-year-old child consulted for a hard purplish papule measuring 8 mm in diameter located in the right lumbar region. Punch biopsy revealed a poorly delineated dermal-hypodermic tumour comprising randomly distributed moderately pleomorphic fusiform cells, arranged in bands or with storiform architecture, certain of which were multi-nucleated. The mitotic index was high (11 mitoses in 10 fields at high magnification). There was no expression by the tumour of melanocytic markers (PS100, Melan-A), histiocytic markers (CD68) or CD34. FISH analysis showed the absence of COL1A1-PDGFB fusion gene. Based on these immunohistochemical and molecular findings, a diagnosis was made of atypical HC with high cellular density. Since the lower margins of the section showed tumoural foci, surgical excision was performed with 5-mm margins. Because the lateral and vertical limits were reached in all cases, a series of five further procedures (the last of was preceded by multiple peripheral biopsies) was necessary to achieve complete excision. These multiple excision procedures resulted in total excision of 25 cm across the longest side. No clinical relapse was seen after 25 months.

DISCUSSION

Cellular or atypical forms of HC carry a high likelihood of post-surgical relapse. They are characterised by marked pleomorphism and high cellular density. In our patient, the extent of the lesion had been greatly underestimated initially, resulting in the need for several surgical procedures in order to achieve complete excision. It is thus important to highlight the predictive factors for this type of tumour in order to enable sufficiently extensive excision, or excision guided by previous biopsies, to be contemplated from the outset. These predictive factors are: young patient age, unusual location (trunk, face, neck), high cellularity, marked mitotic activity and deep extension.

Pleomorphic dermal neoplasms: a review

Pleomorphic neoplasms are typically associated with high-grade malignant behavior, but this does not readily apply to primary cutaneous tumors. Despite morphologic features suggestive of malignancy, atypical fibroxanthoma, the classic example of a pleomorphic dermal neoplasm, is characterized by indolent clinical behavior. Atypical fibroxanthoma is a distinctive clinicopathologic disease affecting sun-damaged skin of elderly males. Histologically, it is often ulcerated and dermal based with pushing growth, characterized by a sheet-like and fascicular growth of pleomorphic epithelioid, spindled, and multinucleated tumor cells with brisk and atypical mitotic activity. However, no positive discriminatory histologic or immunohistochemical features exist. Its diagnosis is one exclusion with a wide differential diagnosis, mainly including other mesenchymal, melanocytic, and epithelial neoplasms. Particular considerations are pleomorphic dermal sarcoma, invasive melanoma, squamous cell carcinoma, metaplastic carcinoma, poorly differentiated cutaneous angiosarcoma, cutaneous leiomyosarcoma, myxofibrosarcoma, variants of fibrous histiocytoma (FH), pleomorphic fibroma, and non-neural granular cell tumor. The behavior of these tumors is varied and ranges from outright malignant to entirely benign, requiring confident diagnosis to reliably predict behavior and guide treatment. Although challenging, because of significant clinical and pathologic overlap, it is usually possible to establish a definitive diagnosis when attention is paid to the often subtle differentiating features. This requires careful tumor sampling, recognition of the subtle distinguishing morphologic features, judicious use and analysis of immunohistochemistry, and interpretation of the findings in the appropriate clinical setting.

(18)F-FDG PET/CT imaging of metastatic atypical fibroxanthoma

We report the F-FDG PET/CT appearance of a metastatic biopsy-proven malignant fibroxanthoma of the ankle. A 41-year-old female patient with a history of scleroderma presented with a fungating mass in the left ankle. Shave biopsy of the overlying skin showed atypical fibroxanthoma (AFX). Staging FDG PET/CT demonstrated a hypermetabolic exophytic soft tissue mass in the left ankle with local extension to bone and widespread metastatic disease including pulmonary parenchyma, nodes, bone marrow, and skeletal muscle. While rare, knowledge of the potential aggressive nature of AFX is important for accurate diagnosis.

Atypical fibrous histiocytoma arising in the perianal area: a case report and review of the literature

Atypical fibrous histiocytoma (AFH) is an uncommon variant of cutaneous fibrous histiocytoma that can display histologic features associated with malignancy. Fewer than 150 cases have been reported in the literature. The majority of these lesions present on the trunk and extremities of middle-aged women. Genital lesions are rare, with one documented case of vulvar AFH and another case of scrotal AFH in the literature. We report an additional case of a 68-year-old woman who was diagnosed with an AFH in an unusual location, the perianal area. Histologically, the lesion was characterized by a nodular fairly well-circumscribed proliferation of large epithelioid macrophages with scattered lymphocytes and mast cells in the background. The atypical macrophages contained enlarged markedly pleomorphic nuclei with prominent nucleoli. Scattered multinucleated "monster cells" and atypical mitoses were observed throughout the lesion. Immunologically, the lesional cells were focally positive when stained with antibodies against CD163 and Factor XIIIa. They were negative for CD34, CD31, desmin, smooth muscle actin, CAM 5.2, keratin 5/6, S100, CD3, CD20, and CD30. The constellation of histologic and immunologic features was most consistent with an AFH. To our knowledge, this case is the first perianal presentation of AFH to date.

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.