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Immunohistochemistry is useful and often necessary for the diagnosis of many histopathological entities, including atypical fibroxanthoma (AFX), which is typically considered a diagnosis of exclusion after ruling out spindle cell melanoma, sarcomatoid carcinoma, and other spindle cell tumors. AFX is a superficial fibrohistiocytic tumor previously believed to be related to pleomorphic sarcoma (formerly known as malignant fibrous histiocytoma), but is now considered a distinct clinicopathological entity. AFXs commonly express CD68, smooth muscle actin, and lysozyme and are usually negative for melanocytic markers such as HMB45 and S100. However, immunohistochemistry can sometimes be misleading, especially when used without other relevant markers in making a histopathologic diagnosis. HMB45 is a glycoprotein marker of premelanosomes and is often helpful in identifying melanoma because it stains melanosomes in the epidermis, dermis, and nevi glycocomplexes. We report a case of AFX which was strongly positive for HMB45, but negative for all other melanocytic markers. This case emphasizes the potential pitfall of relying on a single immunohistochemical marker to make the diagnosis, especially of melanoma, and also is one of the only rare reported cases of AFXs which are HMB45+.

Atypical fibroxanthoma (AFX) is a neoplasm that most commonly occurs on sun-damaged skin of the head and neck in elderly patients and that usually exhibits indolent clinical behavior with complete excision. The granular cell variant of AFX demonstrates overlapping histopathologic features with dermal non-neural granular cell tumor (NNGCT), which typically arises on the extremities of young to middle aged adults with rare reports of regional metastasis. A subset of NNGCT harbors ALK rearrangements and expresses ALK by immunohistochemistry. Here, we present 2 cases of granular cell AFX occurring on the scalp of males aged 73 and 87 with ALK expression by immunohistochemistry and no evidence of an ALK rearrangement on fluorescence in situ hybridization, representing a diagnostic pitfall for NNGCT.

Atypical fibroxanthoma-like amelanotic melanoma is a very rare variant of melanoma that can, if not correctly recognized and framed, lead to diagnostic errors that can potentially cause problems of extreme relevance to patients. Correct knowledge of this entity and the execution of adequate immunohistochemical investigations are the basic conditions for the correct management of this lesion. We report on a case of atypical fibroxanthoma-like amelanotic melanoma, which clinically simulated a fibrohistiocytic lesion, and which created differential diagnostic problems, and finally, we conduct a short review of the literature.

Atypical fibroxanthoma is a rare mesenchymal skin tumor of intermediate malignancy that typically occurs on sun-damaged skin of elderly patients. Histologically, it is composed of pleomorphic cells with hyperchromatic nuclei and abundant cytoplasm, commonly arranged in a spindle cell pattern. Different histologic variants have been described during the past years. We present a case of atypical fibroxanthoma containing a dense inflammatory infiltrate, which in conjunction with the existence of immunoblast-like and Reed-Sternberg-like neoplastic cells could be misinterpreted as a lymphoid neoplasm. Immunohistochemical studies revealed strong positivity of tumor cells for CD10 and negativity for cytokeratins, p63, p40, S100, SOX10, ERG, actin, desmin, B and T-cell markers, BCL6, CD15, and CD30. The inflammatory infiltrate contained a mixed reactive T- and B-cell population with negative T-cell receptor and immunoglobulin heavy rearrangements. We discuss the differential diagnosis of this entity in which clinical, immunohistochemical, and molecular features are essential to avoid the diagnosis of a lymphoproliferative disease.

Summary Atypical fibroxanthoma (AFX) has been considered as the non-infiltrating precursor lesion of pleomorphic dermal sarcoma (PDS), which shows an aggressive clinical behavior, because of its extensive invasion of the deeper skin layers. Although these two tumors may represent two stages of the same disease, it can be difficult to differentiate between them, because of their similar clinical and histological features 1. Furthermore, they must be distinguished from a spindled variant of squamous carcinoma, melanoma and leiomyosarcoma 2. AFX/PDS still remains a diagnosis of exclusion, that needs to combine immunohistochemical markers for a definitive diagnosis. Usually AFX/PDS shows positivity for CD10, CD99, CD68, vimentin and lysozyme, while S100, HMB45, MART-1, cytokeratins, CD34, CD31, desmin and h-caldesmon are absent. We report a case of 89-year-old male, with a history of squamous cell carcinoma removed from the right ear, presented to our department with a recently growing, ulcerated and bleeding 2 cm nodule on the scalp. After surgery the tumor recurred with infiltration to the cranial theca. The final histological diagnosis was “pleomorphic dermal sarcoma” (PDS), which showed an unexpected positivity for HMB45. We present, to the best of our knowledge, the first case of AFX/PDS with an aberrant diffuse expression of HMB45 and an aggressive biological behavior, that leads us to a difficult exclusion diagnosis.

Cutaneous spindle cell squamous cell carcinoma (SpSCC) is a rare and often aggressive subtype of squamous cell carcinoma (SCC), which usually appears in sun-exposed areas, in areas that have received prior ionizing radiation, or in immunosuppressed individuals. SpSCCs are histologically characterized by keratinocytes infiltrating the dermis as single cells with elongated nuclei rather than as cohesive nests or islands and, in contrast to conventional SCC, are lacking features of keratinization. Immunohistochemical studies are useful to distinguish SpSCC from other spindle cell neoplasms, such as spindle cell/desmoplastic melanoma, cutaneous leiomyosarcoma, and atypical fibroxanthoma. We present a rare case of a patient with SpSCC in the gluteal region with regional lymph node metastasis. The patient was treated with wide excision of the tumor, inguinal lymph node dissection, and adjuvant radiotherapy. Cutaneous SpSCC is clinically similar to conventional SCC but can demonstrate more aggressive behavior. This case is rare since it was localized in the gluteal region of an otherwise healthy man.

Undifferentiated melanoma should be considered in the differential diagnosis of sarcomatoid cutaneous malignancies to ensure that patients receive the correct treatment. Dermatopathologists should recognize the pitfalls of relying too heavily on immunohistochemistry to establish this diagnosis and consider ancillary tests, including single-nucleotide polymorphism (SNP) copy number arrays and targeted next-generation sequencing (NGS), when a definitive diagnosis cannot be rendered on a primary or metastatic tumor. This technology can also help to exclude a collision of melanoma and sarcoma when both differentiated and undifferentiated components are juxtaposed. We describe an exceedingly rare, illustrative example of undifferentiated sarcomatoid melanoma presenting as a pedunculated nodule. The clinical context and presence of a small differentiated component helped to establish the diagnosis; however, the transition from differentiated to undifferentiated melanoma was accompanied by an abrupt loss of S100, Sox10, MITF, MelanA, and HMB45 with gain of CD10 and p63 staining. SNP copy number array and NGS revealed shared chromosomal copy number changes and overlapping mutations with additional aberrances detected exclusively in the sarcomatoid component, thereby excluding a collision tumor and confirming our putative impression of melanoma with progression to an undifferentiated sarcomatoid phenotype.

Metabolic reprogramming mediated by hypoxia-inducible factors play a crucial role in many human cancers. HIF-1α is activated under hypoxic conditions and is considered a key regulator of oxygen homoeostasis during tumor proliferation under hypoxia. Aim of this research was to analyze the immunohistochemical expression of HIF-1α, VEGF-A, Glut-1, MCT4, and CAIX in atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS). 21 paraffin-embedded AFX and 22 PDS were analysed by immunohistochemis-try, namely HIF-1α, VEGF-A (referred to as VEGF throughout the manuscript), Glut-1, MCT4, and CAIX. To quantify the protein expression, we considered the percentage of positive tumor cells (0: 0%, 1: up to 1%, 2: 2-10%, 3: 11-50%, 4: >50%) in relation to the staining intensity (0: negative, 1: low, 2: medium, 3: strong). HIF-1α expression (mean ± SD) in AFX (9.33±2.92) was significantly stronger than that in PDS (5.90±4.38; P= 0.007), whereas the expression of VEGF, Glut-1, MCT4, and CAIX did not show differences between AFX and PDS. When comparing all tumors without subgroup stratification, the expression of HIF-1α (P= 0.044) and MCT4 (P= 0.036) was significantly stronger in ulcerated tumors than in tumors without ulceration. Our findings provide the first evidence that HIF-1α-induced metabolic reprogramming may contribute to the pathogenesis of AFX and PDS. HIF-1α expression seems to be higher in AFX than in PDS, and ulcerated tumors show higher expression levels of HIF-1α and MCT4 irrespective of the diagnosis.

Primary cutaneous and mucosal melanoma shows a wide histological spectrum. The correct diagnosis depends upon the demonstration of melanocytic differentiation by recognition of an associated in-situ component or immunohistochemical evidence of a melanocytic phenotype using conventional melanocytic markers, such as S-100, SOX10, Melan-A and HMB-45. Exceptionally, melanomas lose their melanocytic phenotype, at least focally, and show differentiation towards other lineages. Review of the literature shows that de- and trans-differentiation in melanoma is rare but probably under-recognised and under-reported. These often large and frequently ulcerated tumours affect adults and show a wide anatomical distribution, including mucosal sites, although there is a predilection for sun-damaged skin of the head and neck. Histologically, the tumours are biphasic and contain a pre-existing conventional melanoma. The de-differentiated component closely resembles atypical fibroxanthoma, both morphologically and immunohistochemically. Trans-differentiated melanoma may show rhabdomyosarcomatous or spindle cell carcinomatous features. Undifferentiated melanomas are similar tumours in which the conventional melanoma component is absent. Their diagnosis depends entirely upon the clinical context and identification of a classical melanoma driver gene mutation, i.e. BRAF V600E. The diagnosis of these rare and unusual tumours is challenging, and requires thorough tumour sampling and recognition of the background of a pre-existing but often focal conventional melanoma together with molecular analysis.

The finding of a pigmented lesion within another distinct lesion is rare but not unheard of. Here, we describe the presence of an atypical fibroxanthoma within a melanoma in a 72-year-old female referred to the plastics surgery department with a pigmented lesion on her left knee. It was excised in view of clinical suspicion of melanoma. The histopathology report documented a single lesion with two distinct components, namely a melanoma of superficial spreading type with a Breslow thickness of 3.0mm, and a central nodule of atypical fibroxanthoma.

Background Pleomorphic dermal sarcoma (PDS) describes rare dermal-based malignant tumours that are morphologically similar to atypical fibroxanthoma (AFX). PDS may be differentiated from AFX by the presence of one or more of the following histologic features: subcutaneous invasion, tumour necrosis, lymphovascular invasion (LVI), and/or perineural infiltration (PNI). Aims To further define the clinicopathological features, surgical management, and outcomes of PDS primary tumours. Methods and results This study was a retrospective observational case series using a database search from 2012 to 2017. Inclusion criteria required all cases to meet the histopathologic criteria for PDS as confirmed by a specialist soft-tissue histopathologist. A total of n = 17 cases were included with a median age of 78 years (range 66-85). All tumours were located on the head and neck, with 13/17 located on the scalp. Primary treatment was with wide local excision (WLE) in all cases. Median follow-up was 48 months. Local recurrence occurred in 4/17 cases (24%) and distant metastasis in 2/17 cases (12%). Conclusion PDS behaves more aggressively than atypical fibroxanthoma with which it shares a biologic continuum. The optimal surgical management approach is yet to be determined.

An 82-year-old man presented with a right scalp lesion which had been increasing in size. The patient’s medical history was significant for a heart transplant 25 years before, and he was on chronic immunosuppression. Biopsy of the lesion showed atypical fibroxanthoma. The patient underwent an excision of the lesion with split thickness skin graft. Pathology showed fibroxanthoma with negative margins. Over the next 9 months, the patient developed new lesions, which were also excised to negative margins. However, with each new lesion, the histology demonstrated increasing dysplasia and ultimately pleomorphic sarcoma. The patient had a metastatic workup with CT of the chest, which was negative, and he underwent a radical scalpectomy, split thickness skin graft placement and adjuvant radiation therapy. The patient has not developed any new scalp lesions and no evidence of metastasis.

Atypical Fibroxanthoma is an unusual dermal mesenchymal tumor. It especially affects older adults and occurs in areas of sun exposure. We report a 75 years old male with a history of sun exposure without using a hat presenting with a scalp nodule. An incisional biopsy showed an atypical fibroxantoma. In a new surgical procedure, the tumor was completely excised. The tumor relapsed in two occasions after subsequent excisions and the patient was treated with adjuvant radiotherapy avoiding new relapses.

Atypical fibroxanthoma (AFX) or undifferentiated pleomorphic sarcoma (UPS) is a rare malignant neoplastic disease of the skin. At the beginning of the 1960s AFX was described as an independent entity and superficial variant of malignant fibrous histiocytoma (MFH). Since then, many controversies on the classification have arisen mainly because in many cases dedifferentiated neoplasms from other origins were falsely diagnosed as AFX. A relevant deep expansion, the invasion of nerves and vessels or the presence of tumor necrosis are described as being typical for UPS; however, in the first-line they represent risk factors for recurrence. In view of the clinical and histological features it is meaningful to consider AFX and UPS as one disease. In recent years many studies on the molecular pathological background have attempted to make a better classification of the neoplasm, without being able to so far name a certain specific histopathological or molecular pathological characteristic. The AFX/UPS is still in essence a morphological and immunohistochemical diagnosis by exclusion.

Atypical fibroxanthoma and undifferentiated pleomorphic sarcoma, or pleomorphic dermal sarcoma, are rare malignant cutaneous neoplasms existing along a clinicopathologic spectrum. Although these tumors share many similarities, recognition of distinguishing characteristics may predict differences in clinical behavior and outcomes. Salient features defining atypical fibroxanthoma include superficial tumors with minimal high-risk histologic features. Deeper tumors with high-risk histologic features are often clinically aggressive and should be appropriately designated as pleomorphic dermal sarcoma. Surgery remains gold standard in management; tumor extirpation with complete margin control is critical. In the high-risk tumor cohort, comprehensive evaluation and multidisciplinary management is paramount for optimal outcomes.

Background. Atypical fibroxanthoma (AFX) is a tumor that commonly presents on the head or neck in older individuals. Making a definitive diagnosis of AFX is challenging, and frequently, it is hard to distinguish from pleomorphic dermal sarcoma (PDS). There are no clear recommendations regarding the treatment of AFX, but an extensive surgery is actually considered the best option. Electrochemotherapy (ECT) is a novel therapeutic modality of local treatment in which the application of electrical pulses, enhancing cell membrane permeability, allows greater intracellular accumulation of chemotherapy drugs in the skin or subcutaneous tumors. Case Report. We report a case of a 78-year-old male affected by a red, ulcerative, dermal, scalp nodule, which was treated with ECT with a complete clinical response. We have also reported literature data on this topic. Results. In this case, ECT showed to be an effective and safe treatment for recurrent neoplasms of the head and neck, considering the complete response obtained and the absence of disease relapse after two years. Conclusion. To the best of our knowledge, this is the first case report that shows great clinical results using ECT after surgery in relapsed AFX/PDS. However, more studies are needed to confirm our results.

Malignant melanoma (MM) may display highly variable phenotypic diversity, sometimes associated with loss of immunohistochemical melanocytic markers and acquisition of nonmelanocytic lineage of differentiation. Primary cutaneous MM with rhabdomyosarcomatous differentiation is extremely rare with only 5 reported cases in the literature. To date, a chronological progression of a MM to rhabdomyosarcoma has not been conclusively documented. A 96-year-old man underwent a re-excision of an "atypical fibroxanthoma" of the forearm, which revealed a small lentigo maligna melanoma associated with a dominant dermal high-grade spindle cell nodule admixed with a population of malignant polygonal epithelioid cells. On immunohistochemical studies, the spindle cells were completely negative for all melanocytic markers, whereas a small population of polygonal neoplastic cells at the periphery was positive for Desmin and Myo-D1, supporting early rhabdomyosarcomatous transformation. Several subsequent re-excisions demonstrated merely nodules of malignant pleomorphic epithelioid cells with rhabdomyosarcomatous differentiation and devoid of melanocytic markers. In addition, both rhabdomyosarcomatous component and original MM displayed identical mutations. Therefore, the histologic, immunohistochemical, and molecular findings documented for the first time a chronological progression from an invasive MM to a pleomorphic rhabdomyosarcoma through an intermediate stage of undifferentiated sarcoma/atypical fibroxanthoma. Interestingly, subsequent recurrences of pure rhabdomyosarcomatous component displayed skip lesions/microsatellitosis, marked tumor-infiltrative lymphocytes, and rare junctional nests of rhabdomyosarcomatous cells in the epidermis, histologic features that were not described in primary cutaneous rhabdomyosarcoma and therefore could serve as morphologic clues to the diagnosis of rhabdomyosarcomatous transformation in an MM.

Background Atypical fibroxanthomas (AFX) and pleomorphic dermal sarcomas (PDS) are lesions of the skin with overlapping histologic features and unspecific molecular traits. PDS behaves aggressive compared to AFX. Thus, a precise delineation, although challenging in some instances, is relevant. Methods We examined the value of DNA-methylation profiling and copy number analysis for separating these tumors. DNA-methylation data were generated from 17 AFX and 15 PDS using the Illumina EPIC array. These were compared with DNA-methylation data generated from 196 tumors encompassing potential histologic mimics like cutaneous squamous carcinomas (cSCC; n = 19), basal cell carcinomas (n = 10), melanoma metastases originating from the skin (n = 11), leiomyosarcomas (n = 11), angiosarcomas of the skin and soft tissue (n = 11), malignant peripheral nerve sheath tumors (n = 19), dermatofibrosarcomas protuberans (n = 13), extraskeletal myxoid chondrosarcomas (n = 9), myxoid liposarcomas (n = 14), schwannomas (n = 10), neurofibromas (n = 21), alveolar (n = 19) and embryonal (n = 17) rhabdomyosarcomas as well as undifferentiated pleomorphic sarcomas (n = 12). Results DNA-methylation profiling did not separate AFX from PDS. The DNA-methylation profiles of the other cases, however, were distinct from AFX/PDS. They reliably assigned to subtype-specific DNA-methylation clusters, although overlap occurred between some AFX/PDS and cSCC. Copy number profiling revealed alterations in a similar frequency and distribution between AFX and PDS. They involved losses of 9p (22/32) and 13q (25/32). Gains frequently involved 8q (8/32). Notably, a homozygous deletion of CDKN2A was more frequent in PDS (6/15) than in AFX (2/17), whereas amplifications were non-recurrent and overall rare (5/32). Conclusions Our findings support the concept that AFX and PDS belong to a common tumor spectrum. We could demonstrate the diagnostic value of DNA-methylation profiling to delineating AFX/PDS from potential mimics. However, the assessment of certain histologic features remains crucial for separating PDS from AFX. Electronic supplementary material The online version of this article (10.1186/s13569-019-0113-6) contains supplementary material, which is available to authorized users.

There are 3 types of leiomyosarcoma of the skin: dermal, subcutaneous, and metastatic cutaneous. Dermal leiomyosarcoma arises from smooth muscle fibers in arrector pili muscles, genital dartos muscles, and the nipple-areola complex. It is an intermediate-grade tumor associated with a tendency for local recurrence (24%) and low metastatic potential (4%). Subcutaneous leiomyosarcoma originates from smooth muscle in blood vessel walls and has higher rates of local recurrence (37%) and metastasis (43%). Plemorphic dermal sarcoma typically affects elderly patients and arises in sun-exposed areas (e.g., the scalp). Its histologic and immunohistochemical characteristics are similar to those of atypical fibroxanthoma, but it is more aggressive (metastasis rate of 10-20%). Histologically, it can be distinguished from atypical fibroxanthoma by the observation of subcutaneous tissue invasion, perineural invasion, and foci of necrosis.

Malignant mesenchymal tumors of oropharyngeal mucosa are rare. Those with fibroblastic and histiocytic differentiation in the skin are called atypical fibroxanthoma (AFX) and in the soft tissue undifferentiated pleomorphic sarcoma (UPS). Here we present a case of an older patient with a history of multiple basal cell carcinomas and recently with a rapidly growing polypoid lesion in the mucosa of posterior oropharyngeal wall with AFX/UPS morphology. The differential diagnosis, histological pitfalls of this poorly characterized mesenchymal lesions, and the challenges associated with treatment are discussed.

Atypical fibroxanthoma (AFX) and pleomorphic dermal sarcoma (PDS) are rare tumors developing in chronically sun-exposed skin. Clinicopathological features are similar, but they differ in prognosis, while PDS has a more aggressive course with a higher risk for local recurrence and metastases. In current clinical practice, they are diagnosed by exclusion using immunohistochemistry. Thus, stringent diagnostic criteria and correct differentiation are critical in management and treatment for optimal outcomes. This retrospective single-center study collected clinicopathological data and tumor samples of 10 AFX and 18 PDS. Extracted genomic DNA from tumor specimens was analyzed by a next-generation sequencing (NGS) platform (FoundationOne-CDx™). Among 65 identified mutations, TP53 inactivating mutations were observed in all tumor specimens. In both AFX and PDS, the known pathogenic gene alterations in CDKN2A, TERT promoter, and NOTCH1 were frequently present, along with high mutational burden and stable Micro-Satellite Instability status. The mutational profiles differed only in ASXL1, which was only present in AFX. Further differences were identified in likely pathogenic and unknown gene alterations. Similarities in their genomic signatures could help to distinguish them from other malignancies, but they are not distinguishable between each other using the FoundationOne-CDx™ NGS panel. Therefore, histological criteria to determine diagnosis remain valid. For further insight, performing deep tumor profiling may be necessary.