Cutaneous fibrohistiocytic tumours - an update

[Pediatric cutaneous mesenchymal tumors: How to cope with small samples?]

This review article deals with the diagnosis of superficial mesenchymal tumours in children. This is not a comprehensive review, but it focuses on the issue of diagnosis on small samples, especially on fine needle biopsies, which are more and more frequent. A selection of difficult diagnostic situations are discussed, including the case of spindle-cell tumours with variable adipocytic component, some fibrohistiocytic tumours, myofibromas, and vascular tumours. The key messages are the technical requirements in relation to the small sample size, the essential nature of clinical data in paediatric pathology and primarily the age, which is crucial not only for establishing the differential diagnosis but also for choosing the relevant ancillary techniques, and last, the utility of cytogenetics, mainly FISH, and of wisely used molecular biology techniques.

Clinicopathologic Analysis of Dermatofibroma: A Retrospective Study of 165 Cases

Dermatofibroma (DF), also known as benign fibrous histiocytoma, is a common benign skin tumor whose clinicopathologic features and pathogenesis remain only partially understood. In this retrospective study, 165 cases of DF diagnosed between 2018 and 2024 were analyzed to characterize demographic, clinical, and histopathologic profiles. Data regarding patient age, gender, horizontal tumor size, anatomical location, and pathological subtypes were extracted from digital pathology archives. Statistical analyses revealed that male patients exhibited significantly larger horizontal tumor sizes compared to female patients (P = 0.027). Additionally, the tumor location was significantly associated with size, with lesions in the subcutaneous tissue showing larger mean horizontal dimensions than those in the reticular or papillary dermis (P = 0.032). These findings suggest that gender, tumor location, and pathological subtype are influential factors in DF growth, providing further insight into its clinical behavior and potential underlying mechanisms. These findings highlight the importance of considering patient gender and tumor location in the clinical management of DF, potentially guiding personalized treatment strategies and improving patient outcomes.

Updated Review of Cellular Dermatofibroma: Benign or Not?

BACKGROUND

Cellular dermatofibromas (CDFs) are uncommon benign fibrous histiocytomas with histologic patterns resembling malignancies. Despite their benign nature, CDFs can recur and metastasize. Physicians are uncertain about the management of CDF, given its resemblance to dermatofibrosarcoma protuberans.

OBJECTIVE

This review aims to review CDF's clinical and histologic features, differentiate it from similar presenting malignancies, and discuss treatments and outcomes for better clinical management.

MATERIALS AND METHODS

In April 2024, a PubMed and Google Scholar search was completed using "cellular dermatofibroma" through the University of California Davis Medical School's library databases. The search included meta-analyses, randomized controlled trials, observational studies, reviews, and case studies published within the past 70 years. References from retrieved articles were utilized as additional resources.

RESULTS

Clinical signs of CDF include firm, skin-colored to hyperpigmented lesions usually larger than 2 cm, typically on extremities. Currently, there are no definitive indicators for CDF recurrence or metastasis. Diagnosis requires microscopic and histopathologic examination, with surgical excision as the preferred treatment. Recurrence is not uncommon, while metastasis is rare.

CONCLUSION

CDFs often develop in young/middle-aged adults with a tendency to recur and in rare cases can metastasize. Future studies could explore lesion characteristics that are associated with potential for recurrence and metastasis.

Epithelioid Fibrous Histiocytoma Is on a Continuum With Superficial ALK-rearranged Myxoid Spindle Cell Neoplasm: A Clinicopathologic Series of 35 Cases Including Alternate RET and NTRK3 Fusions

Anaplastic lymphoma kinase (ALK) rearrangements drive most examples of epithelioid fibrous histiocytoma (EFH) and have been reported in an emerging family of receptor tyrosine kinase (RTK) fusion-positive mesenchymal neoplasms, including superficial ones described under the rubric of "superficial ALK-rearranged myxoid spindle cell neoplasm" (SAMS). Here, we describe 35 superficial tumors with SAMS morphology, which occurred in 18 females (51%) and 17 males at a median age at presentation of 39 years (range: 6 to 82 y). Most tumors occurred on the lower extremity (25 tumors; 71%), followed by upper extremity (5; 14%), trunk (3; 9%), and face (2; 6%). Nine tumors were reported to have grown slowly before presentation, including >10 years in 2 cases. Tumors occurred primarily in the dermis (32 tumors; 91%) or subcutis (3; 9%); 8 dermal tumors extended into the subcutis. Median tumor size was 1.3 cm (range: 0.5 to 8.0 cm). Clinical follow-up was available for 12 patients (34%; range: 2 mo to 21 y; median: 2.7 y), none of whom experienced metastasis. One incompletely resected tumor recurred locally at 19 months, and no other patients experienced recurrence. Histologically, tumors were characterized by bland spindle-to-ovoid cells showing whorled growth and myxoid-to-collagenous stroma. Recurrent features included an epidermal collarette (19/30; 63%), perivascular hyalinization (20/35; 57%), amianthoid collagen (14/35; 40%), and metaplastic ossification (2/35; 6%). Immunohistochemistry (IHC) demonstrated expression of ALK (24/31; 77%), CD34 (15/21; 71%), EMA (17/28; 61%), and S-100 (9/32; 28%). Eleven tumors showed hybrid morphologic features between EFH and SAMS; 9 of them (82%) showed cytomorphology typical of EFH but with whorled growth, myxoid stroma, and/or regions of spindle cell morphology. Two hybrid tumors showed sharp transitions between a region characteristic of EFH and a region characteristic of SAMS, with a concomitant sharp transition in EMA, CD34, and S-100 expression by IHC. Sequencing revealed ALK fusions in 15 of 19 tumors: 2 each with fusion partners FLNA, SQSTM1, and VCL, and 1 each with COL1A2, DCTN1, EML4, FXR1, MPRIP, PLEKHH2, PRKAR1A, SPECC1L, and TLN2. Thirteen of 14 ALK-rearranged tumors expressed ALK by IHC. Three tumors negative for ALK fusions instead harbored alternate RTK fusions (NCOA4::RET, TRIM27::RET, and VIM::NTRK3), and 1 tumor was negative for RTK alterations. CDKN2A/B deletions were found in 2 tumors with ALK fusions and both tumors with RET fusions. SAMS is on a morphologic and molecular genetic spectrum with EFH, with a similar body site distribution, frequent clinical presentation as an exophytic skin tumor, and invariably benign outcomes; we conclude that SAMS should be considered a histologic variant of EFH. Some morphologically typical examples harbor alternate RET and NTRK3 fusions, such that SAMS is not an appropriate designation for this morphologic class; instead, to highlight the clinicopathologic similarities to EFH, we propose the diagnostic term "myxoid spindle cell variant of epithelioid fibrous histiocytoma."

Perforating Fibrous Histiocytoma Mimicking Keratoacanthoma: A Case Report

A 31-year-old male presented with a firm, well-demarcated, erythematous, crateriform, and ulcerated nodule in the left lumbar region, which persisted for 3 months. Clinically, a keratoacanthoma was suspected. The histological analysis was consistent with perforating fibrous histiocytoma, a rare histopathologic variant of fibrous histiocytoma. To our knowledge, this is the third case reported in the literature.

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.

Cutaneous Syncytial Myoepithelioma with Positive CD34 Immunohistochemical Staining: An Unusual Tumor and a Challenging Diagnosis

Cutaneous syncytial myoepithelioma (CSM) is a rare type of cutaneous neoplasm that typically presents as a solitary and well-circumscribed nodule on the skin. It predominantly occurs on the upper and lower extremities of adult patients. Immunohistochemically, CSM is characterized by the co-expression of smooth muscle and epithelial markers. Fluorescence in situ hybridization (FISH) targeting the EWSR1 gene rearrangement is an important diagnostic tool for CSM. In our case report, we found the focal positivity for CD34, which has never been previously observed; this was mostly confined to a central area of the neoplasm.

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.

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.

Multiple benign fibrous histiocytomas of the mandible: A case report and review of the literature

Benign fibrous histiocytoma (BFH) mostly occurs on the skin of the extremities, while it is unusual to manifest on the bone and mandibular involvement of BFH is even rarer. The present study reports a case of BFH in a 42-year-old female who had a slowly progressive swelling of the bilateral mandible and slight facial asymmetry over a period of 4 months. However, the outcome of this patient was unsatisfactory, with the first and second recurrence observed 16 and 46 months after surgery, respectively. The present case suggests that BFH has a risk of recurrence after transoral curettage. Regular follow-up is advised to detect tumor recurrence after the surgery of transoral curettage.

Malignant Superficial Mesenchymal Tumors in Children

Malignant superficial mesenchymal tumors are a very diverse group of neoplasms with few clinical and radiological discriminatory factors. Hence, some of these cancers are rarely suspected based on clinical and radiological grounds, others may be easily misdiagnosed, and the histological analysis of a biopsy or resection is central in the diagnostic process. In children, the age at presentation is a major element of the differential diagnosis. Some tumors have a very distinct epidemiology, while others may be seen at any age. More recently, the advances in molecular biology have greatly improved the diagnosis of mesenchymal tumors and new entities are still being described. In the present review, we provide an overview of the diversity of malignant superficial mesenchymal tumors in children, including new and/or rare entities. We discuss the important diagnostic features, be they clinical, histological, or molecular. Special attention was given to the genetic features of these tumors, particularly when they were helpful for the diagnosis or treatment.

Rare Palisading Variant of Dermatofibroma

ABSTRACT

Dermatofibromas (DFs) are benign lesions that typically present as firm papules or nodules on the legs of young- to middle-aged adults. DFs are histologically characterized by a dermal proliferation of spindled fibrohistiocytic cells forming intersecting fascicles and showing collagen entrapment. The palisading variant of DF was first described in 1986 and often presents as a dome-shaped nodule on the digits. Histologically, palisading DFs demonstrate central areas of nuclear palisading in parallel rows resembling Verocay bodies, with more typical areas of DF located peripherally. We report a case of a 33-year-old Hispanic woman who presented with a history of an asymptomatic, slow-growing lesion on her left arm present since her teenage years. Physical examination revealed a solitary, firm brown-to-white 5-mm papule on the left upper arm. A biopsy was performed and revealed a proliferation of spindle cells palisading around areas of hyalinized collagen. The many histologic variants of DF can sometimes create diagnostic confusion. Previously described cases of palisading DFs in the literature showed palisading resembling Verocay bodies and thus raising concern for a schwannoma or other neoplasm that display a "rippled" pattern. Our case is unique in that the architecture of the palisading areas instead resembled a necrobiotic granulomatous process such as granuloma annulare or a rheumatoid nodule at low power.

A rare case of congenital plexiform fibrohistiocytic tumor of the foot in a 4-year-old boy: case report and literature review

The plexiform fibrohistiocytic tumor (PFHT) is an infrequent soft-tissue neoplasm with uncertain biological behavior. We report a rare congenital PFHT case in a 4-year-old boy, treated with wide excision and skin grafting. After a 52-month follow-up, no recurrence, regional or distant metastases were documented. A literature review on the management of PFHTs is reported.

Solitary adult xanthogranuloma in external auditory canal: Cyto-histopathological correlation of an uncommon entity at an uncommon site

Juvenile xanthogranulomas (JXG) are the most common type of self-limiting non-Langerhans cell histiocytosis (LCH) usually presenting in infancy and early childhood. Clinically, they present as solitary to multiple rounded cutaneous nodules which resolve over time. Adult type xanthogranulomas (AXG), though histologically similar to JXG, are usually single and do not regress spontaneously. AXG arising in the external auditory canal (EAC) is a rare occurrence with very few cases reported in literature. We present a case of AXG in a 48-year-old man, arising from the right EAC. This case is unique as it is the only case to be described with both cytology and histology correlation. On cytology, smears showed scattered foamy histiocytes, inflammatory cells and thick stromal fragments. Cytology differential diagnoses of xanthomatous lesion, benign fibrous histiocytoma (BFH) and ceruminous adenoma were given; final diagnosis was deferred to histopathology which confirmed it to be an AXG. Thus, it is important to keep the diagnosis of AXG in mind while dealing with solitary polypoidal lesions in EAC showing prominent foam cell component. Lipidised BFH forms a close differential diagnosis, however can be excluded by subtle points on cytology and on histopathology.

Atrophic Dermatofibroma: A Comprehensive Literature Review

INTRODUCTION

An atrophic dermatofibroma is a benign fibrohistiocytic neoplasm. It typically presents as an asymptomatic patch with a depressed central area.

METHODS

The PubMed database was used to search the following words: atrophic, dermatofibroma, elastic and fibers. The relevant papers and their references generated by the search were reviewed. Images of the clinical and pathological features of two patients with an atrophic dermatofibroma are presented. In addition, a comprehensive review of the characteristics of this unique dermatofibroma is provided.

RESULTS

An atrophic dermatofibroma has been reported in 102 patients: 53 women, 11 men and 38 individuals whose gender was not provided. It typically appeared as an asymptomatic solitary patch with a central umbilication-most commonly on the shoulder or lower extremity or back-of women aged 48 years or older. Dermoscopy typically showed white scar-like patches; a patchy pigment network was also noted in some lesions. The pathology of an atrophic dermatofibroma has the same features that can be observed in a common fibrous dermatofibroma; there is acanthosis, basal layer hyperpigmentation, and induction of basal cell carcinoma-like features, hair follicle formation or sebaceous hyperplasia in the epidermis and a proliferation of spindle-shaped fibroblasts in the dermis. However, atrophic dermatofibromas also demonstrate depression of the central surface and thinning of the dermis; in many cases, the dermal atrophy is at least 50%. Elastic fibers are either decreased or absent. Similar to non-atrophic dermatofibromas, the immunoperoxidase profile of atrophic dermatofibromas is factor XIIIa-positive and cluster of differentiation 34 (CD34)-negative. The pathogenesis of atrophic dermatofibromas remains to be established.

CONCLUSION

An atrophic dermatofibroma is an uncommon benign variant of a dermatofibroma. The diagnosis can be suspected based on clinical features and dermatoscopic findings. A biopsy of the lesion will confirm the diagnosis. Periodic evaluation of the lesion site is a reasonable approach to the management of the residual tumor.

HL, Ruas CP, Jorge VM. Scanning electron microscopy of dermatofibroma

Dermatofibroma is a proliferation of spindle cells located in the dermis. We used scanning electron microscopy to examine two histologically confirmed lesions and observed preserved collagen bundles in the perilesional area. In the lesional area, the collagen was denser, without formation of bundles. Higher magnification showed collagen with mesh-like appearance similar to stretched tufts of cotton. Very high magnification evidenced the tufts of cotton and spindle cells measuring 2 to 12 microns.

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.

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.

Ulcerated congenital plexiform fibrohistiocytic tumor: Case report and literature review

A newborn boy presented with a progressively infiltrating and painful congenital ulcerated plaque on the back of his left foot. A partial excision was performed and histopathologic examination confirmed a diagnosis of a plexiform fibrohistiocytic tumor. This rare tumor usually appears in children and adolescents, with congenital presentations even more uncommon. This case details the exceptional presentation of a congenital ulcerated plexiform fibrohistiocytic tumor with a review of the current literature.

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.

Distinguishing a Rare Variant of Lipidized Dermatofibroma from Nonlipidized Dermatofibromas in a Patient with Hypothyroidism and Alopecia Areata

Introduction. Lipidized dermatofibromas represent rare and often underrecognized variants of dermatofibromas. Histologically, dermatofibromas are composed of fibroblast-like spindle cells, foam cells, giant cells, siderophages, lymphocytes, capillaries, collagen fibers, and hyaline dermal collagen fibers. Lipidized dermatofibromas are characterized by numerous foam cells, Touton giant cells, and hyalinized wiry collagen in the stroma. Case report. We present a case of a 31-year-old woman with a history of hypothyroidism and alopecia areata, presenting with an enlarging 8 mm, firm erythematous nodule on her upper-mid back. Biopsy examination showed a cellular proliferation of spindle cells with peripheral collagen trapping and cholesterol clefts with associated foam cells and sclerosis, staining weakly positive for Factor XIIIa and negative for CD34. The diagnosis of a benign lipidized dermatofibroma was rendered. Conclusion. Lipidized dermatofibromas are rare histologic variants of dermatofibromas, biologically indolent, and should be distinguished from other cutaneous foamy histiocytic lesions, particularly xanthomas, which may alter patient management.

Anaplastic Lymphoma Kinase in Cutaneous Malignancies

Anaplastic lymphoma kinase (ALK) is a receptor tyrosine kinase that has been implicated in the pathogenesis of a variety of neoplasms. As suggested by its name, ALK was first described as part of a translocation product in cases of anaplastic large-cell lymphoma, with other genetic and cytogenetic ALK mutations subsequently coming to attention in the development of many other hematologic and solid organ malignancies. ALK has now been shown to play a role in the pathogenesis of several cutaneous malignancies, including secondary cutaneous systemic anaplastic large-cell lymphoma (ALCL) and primary cutaneous ALCL, melanoma, spitzoid tumors, epithelioid fibrous histiocytoma, Merkel cell carcinoma, and basal cell carcinoma. The characterization of ALK-positivity in these cutaneous malignancies presents exciting opportunities for utilizing ALK-targeted inhibitors in the treatment of these diseases.

Myxoid Plexiform Fibrohistiocytic Tumor Masquerading as Ganglion Cyst: A Case Report and Literature Review

Background. Plexiform fibrohistiocytic tumor is a distinctive mesenchymal neoplasm of low-grade malignancy, with the capacity for biphasic differentiation toward a fibroblastic or histiocyte-like morphology. Clinically, these lesions affect different areas of the body and appear as painless, slowly growing, dermal or subcutaneous masses. To date, only three cases of myxoid variant have been reported in the English literature. Case Presentation. A 45-year-old female patient presented with a subcutaneous nodule in the right popliteal fossa. The initial impression was a benign ganglion cyst. The soft tissue tumor has been treated by local excision. The histopathological and the immunohistochemical findings supported the diagnosis of myxoid plexiform fibrohistiocytic tumor. The postoperative course was uneventful, and the patient received regular follow-up examination. She is alive without any recurrence. Conclusions. This case demonstrates how to distinguish this distinctive plexiform fibrohistiocytic tumor from other problematic soft tissue tumors. It is also remarkable for its rarely reported extensive myxoid change. Currently, there is no clear-cut correlation between the clinicopathologic findings and the behavior of this unusual variant.

Selected benign cutaneous lesions that may simulate melanoma histologically

As cutaneous melanomas manifest a wide spectrum of clinical and pathologic presentations, several other lesions enter into their differential diagnosis. This article considers those entities, including melanocytic hyperplasia, cellular nodules in congenital nevi, atypical lentiginous melanocytic proliferations, "special site" nevi, epithelioid histiocytoma, neurothekeoma, cellular schwannoma, and proliferating scars.

S-100 Negative Granular Cell Tumor of the Oral Cavity

Classic granular cell tumor is a mesenchymal neoplasm that commonly occurs on the skin, but is not infrequently found in the oral cavity, primarily on the dorsal tongue. Diagnosis is usually straightforward with hematoxylin and eosin stained slides. Immunohistochemical studies on classic granular cell tumor shows positive immunostaining for S-100 and vimentin, while CD68 is variably positive. We report a case of otherwise unremarkable oral granular cell tumor that was immunohistochemically negative for S-100, and positive for vimentin and CD68, and discuss the differential diagnosis. The results of the immunohistochemical studies in our case are compared with those of classic S-100 positive oral granular cell tumors, as well as cutaneous and oral S-100 negative granular cell tumors. Classic S-100 positive granular cell tumors and S-100 negative granular cell tumors of the oral cavity can only be distinguished by immunohistochemical studies; however, the necessity of this distinction is unclear, as both are benign lesions in which recurrence is unlikely.

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.

[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.

Variants of dermatofibroma--a histopathological study

Several variants of dermatofibroma have been described. They are essentially distinguished by their clinical and histopathological features. To review the mainfeaturesof these variants, a retrospective study of skin biopsies and tissue excisions of dermatofibromasperformed in the dermatology and venereology service at the Hospital Garcia de Orta between May 2007 and April 2012 was carried out. During that period, 192 dermatofibromas were diagnosed in 181 patients, the lesions being more common in women. Median age of the study population was 48 years. The most common lesion site was the limbs (74% of patients). The histopathological types found were common fibrous histiocytoma (80%) and the aneurysmal (5.7%),hemosiderotic (5.7%), epithelioid (2.6%), cellular (2.1%), lipidized (2.1%), atrophic (1.0) and clear cell (0.5%) variants. Based on these findings, this review focuses on the clinical and histological features of the various variants of dermatofibroma in terms of their clinical presentation, distinct histopathological features, differential diagnosis and prognosis.

[Cutaneous sarcomas: update on selected fibrohistiocytic and myofibroblastic tumors]

BACKGROUND

Malignant fibrohistiocytic tumors are a heterogeneous group of mesenchymal neoplasms that may occur in the skin and subcutaneous tissues.

DIAGNOSIS

Diagnosis of these tumors may be difficult, as they are rare, and a wide morphological diversity of types and subtypes has been described. In this update, relevant aspects of selected entities like dermatofibrosarcoma protuberans, desmoid tumor, atypical fibroxanthoma, pleomorphic dermal sarcoma, and myxofibrosarcoma are discussed according to the WHO classification of 2013. The typical clinical feature of these tumors is their mostly asymptomatic appearance. For diagnosis, the histologic workup is therefore the key feature; herein immunohistochemistry as well as molecular diagnostics become increasingly important.

THERAPY

The primary treatment for locally resectable tumors is complete surgical removal; chemotherapy, radiation, and targeted therapies with kinase inhibitors are available for inoperable and metastatic disease.

Plexiform fibrohistiocytic tumor of the foot: a case report

Plexiform fibrohistiocytic tumors are rare, small, ill-defined, solitary masses found in the deep dermis or subcutaneous tissues. These tumors will ordinarily be slow-growing masses that almost solely occur in children and young adults. They have had a greater prevalence in the upper extremity than in the lower extremity, with limited reports of this lesion in the lower extremity. We report a small painful mass found in the central plantar heel of a 12-year-old male.

Dermatofibroma of the face: a clinicopathologic study of 20 cases

INTRODUCTION

Dermatofibroma is one of the most common benign skin tumors. It typically develops on the lower limbs between the third and fifth decade of life and is more common in women. Clinical diagnosis is often straightforward. Dermatofibromas are associated with a very low rate of local recurrence following excision.

OBJECTIVES

To describe the clinical and histologic features of dermatofibroma of the face based on our experience.

MATERIALS AND METHODS

Descriptive retrospective study of the clinicopathologic features of dermatofibromas of the face diagnosed at the dermatology department of Hospital General Universitario de Valencia between 1990 and 2012.

RESULTS

Twenty cases of dermatofibroma of the face (1.11% of all dermatofibromas diagnosed) were studied. The age at onset varied widely, from 28 to 84 years. The mean age at onset was 57.15 years and the median was 54 years. There were 11 women and 9 men. Mean follow-up was 83 months and there were no local recurrences. All the tumors were confined to the papillary and reticular dermis and the storiform pattern was the most common growth pattern observed.

CONCLUSIONS

This study of facial dermatofibromas diagnosed at our hospital over a period of 22 years suggests that the face is an uncommon site but that dermatofibromas in this location behave similarly to those occurring elsewhere on the body.