SOX-10 and MiTF expression in cellular and 'mixed' neurothekeoma.

BACKGROUND: Neurothekeoma and nerve sheath myxoma have long been interpreted as related tumors that share nerve sheath linage. Lack of S100 expression in neurothekeoma and similarities of gene expression profiles between neurothekeoma and fibrohistiocytic tumors have created reasonable doubt about this concept. SOX-10 represents a marker for schwannian and melanocytic differentiation, and is expressed in other tumors of nerve sheath linage. Microphthalmia transcription factor (MiTF) expression has been repeatedly reported in cellular neurothekeoma in the recent literature and was proposed as a helpful marker in this entity. METHODS: We investigated 25 cases of cellular neurothekeoma, 8 cases of mixed neurothekeoma and 1 case of nerve sheath myxoma for the expression of SOX-10, MiTF, S100, NKI/C3, Melan-A and smooth muscle actin (SMA) using immunohistochemistry. RESULTS: A lack of SOX-10 expression was demonstrated in 100% of cellular and mixed neurothekeomas, but was present in the case of nerve sheath myxoma. More than two thirds of neurothekeomas showed very focal or no reactivity with MiTF. CONCLUSIONS: Our data suggest that neurothekeoma and nerve sheath myxoma are unrelated, and that cellular and mixed neurothekeoma may not be of nerve sheath lineage. In addition, MiTF should not be regarded as a useful marker in neurothekeoma.

A benign cutaneous plexiform hybrid tumor of perineurioma and cellular neurothekeoma.

There are several recent reports describing hybrid peripheral nerve sheath tumors showing a biphasic component of neoplastic cells. These combinations include a mixture of neurofibroma and schwannoma, schwannoma and perineurioma, neurofibroma and perineurioma, and perineurioma and granular cell tumor. A case of a triphasic combination of neurofibroma, schwannoma, and perineurioma has also been described. We describe the clinicopathologic and immunohistochemical characteristics of 9 cases of a benign cutaneous plexiform nerve sheath tumor located on the lips and exhibiting hybrid features of perineurioma and cellular neurothekeoma. Clinically, lesions were solitary dome-shaped papules located on the lips. Histopathologically, the neoplasms consisted of well-circumscribed but uncapsulated dermal nodules with a plexiform pattern. They were composed of nests or rounded aggregations of neoplastic cells embedded in a slightly myxoid stroma. Within the aggregates, cells were distributed in a storiform and lamellar pattern. Immunohistochemically, most neoplastic cells expressed strong immunoreactivity for S100A6, MiTF, NKI/C3, PGP9.5, EMA, and NSE, whereas variable, focal, and weaker positivity for CD34, claudin-1, and Glut-1 was seen in some cases. On the basis of these findings, we believe that this neoplasm is a distinctive benign cutaneous plexiform nerve sheath tumor with histopathologic and immunohistochemical hybrid features of perineurioma and cellular neurothekeoma.

Cutaneous epithelioid angiomatous nodule arising in capillary malformation.

Cutaneous epithelioid angiomatous nodule (CEAN) represents a rare, benign vascular lesion described by Brenn and Fletcher in 2004. To the best of our knowledge, the development of CEAN in a pre-existing vascular malformation has not been previously reported. A 52-year-old Japanese woman presented with multiple erythematous papules developed on violaceous macule of the right back that had been diagnosed as capillary malformation (CM) in childhood. Histopathological examination of one erythematous papule revealed a relatively well-circumscribed nodule composed mostly of epithelioid cells in the dermis. Abnormal dilated vessels were also identified around the lesion in the dermis, suggesting a CM. Immunohistochemically, the epithelioid cells were positive for CD31 and CD34. Staining for α-smooth muscle actin highlighted pericytes with epithelioid features. These findings were consistent with a diagnosis of CEAN arising in CM. The excised specimens of other erythematous papules revealed pyogenic granuloma (PyG) with focal epithelioid morphology accompanied by CM. We present the first reported case of CEAN arising in CM. Considering the histopathological findings, we speculate that CEAN of our case could be associated with PyG developed in pre-existing CM, and may thus be a variant of PyG with a mostly epithelioid appearance.

Pseudolymphomatous tumid lupus erythematosus of the oral mucosa.

Oral lesions are frequent complications of systemic lupus erythematosus, but only ulceration is included in the 1982 American College of Rheumatology revised criteria. Because the lack of a uniform classification, a range of ulcerative and keratotic lesions are typically described. In this report we describe a unique progressive irregularly cobblestoned and vegetating plaque of the oral mucosa with clinical and histological features mimicking a cutaneous lymphoma. Despite the papillomatous and extensive nature of the lesions and the dense lymphoid infiltrate with follicle formation suggesting a malignant lymphoproliferative process, the slow progression coupled with a mixed cell infiltrate and polyclonality supported a diagnosis of pseudolymphoma. Recognition of this entity is important to prevent diagnosing them as a malignant lymphoma. As well as with the other mucosal lesions in lupus erythematosus, this pseudolymphomatous variant should be added to the disease spectrum.

Podoplanin expression in fibrous histiocytomas and cellular neurothekeomas.

Podoplanin, also recognized by the monoclonal antibody D2-40, is a mucin-type transmembrane glycoprotein that is highly expressed in lymphatics and in a range of vascular and nonvascular proliferations. Recently, podoplanin has been detected in fibrous histiocytomas (FHs) and proposed to represent a potentially useful marker in the diagnostic evaluation of this lesion. There is, however, limited data concerning podoplanin expression in FH and its morphological mimics. Cellular neurothekeomas (CNs) are rare cutaneous neoplasms of uncertain histogenesis that often morphologically mimic FH. In this study, we reviewed our experience with podoplanin expression in FH (n = 30), especially in comparison to CN (n = 15). In addition, we also immunostained a selected group of other mesenchymal lesions that may fall within the differential diagnosis of FH for podoplanin, including dermal nerve sheath myxoma (n = 2), dermatofibrosarcoma protuberans (N = 8), and plexiform fibrohistiocytic tumor (n = 2). Podoplanin expression was observed in a significant subset of FHs (26/30, 86.6%) and in all CNs (15/15, 100%), whereas DFSPs, dermal nerve sheath myxomas, and plexiform fibrohistiocytic tumors were all negative. To the best of our knowledge, this is the first report demonstrating podoplanin expression in CN. Expression of podoplanin in CN represents a potential pitfall in the use of this antibody for diagnostic evaluation of FH. However, podoplanin may be of value as an adjunct to morphological examination in assessment of problematic lesions falling within the differential diagnosis of FH and CN.

Procollagen 1 and Melan-A expression in desmoplastic melanomas.

The histopathologic diagnosis of desmoplastic melanoma (DM) is usually based on typical conventional microscopic findings coupled with expression of S100 protein by neoplastic cells. Important differential diagnostic considerations include atypical fibroxanthoma (AFX) and spindle cell squamous carcinoma. Spindle cell squamous cell carcinoma is characterized by positivity for cytokeratin, whereas the diagnosis of AFX has been one of exclusion. Procollagen 1 (PC1) has been identified as a relatively sensitive marker of AFX. In this study, we sought to analyze the expression of PC1, S100 protein, and Melan-A in a series of 37 DMs (27 males and 10 females; ages 36-92 years, mean age 74 years). All lesions displayed a spindle cell morphology with varying degrees of desmoplasia. The neoplastic cells avidly expressed S100 protein in 37 of 37 neoplasms. A complete lack of PC1 expression was noted in 24 of 37 (64.9%). There was a weak PC1 expression by 9 DMs (24.3%) and a moderate expression by 4 DMs (10.8%). Melan-A expression was found in 19 of 37 DMs (51.4%), but in 10 lesions, the expression was only faint and focal. We conclude that PC1 labeling of DM is not uncommon but poses little risk for misdiagnosis, provided the stain is performed as part of panel that includes S100 protein. Melan-A offers little for the diagnosis of DM, as less than a quarter of lesions exhibit a strong reaction with this antibody. It is critical to employ a broad panel of antibodies, including S100 protein, Melan-A, cytokeratin, PC1, and others, in the immunohistochemical evaluation of spindle cell neoplasms of the skin.

The African Teledermatology Project: Providing access to dermatologic care and education in sub-Saharan Africa.

BACKGROUND: Telemedicine allows health providers in remote areas to transfer information for medical consultation anywhere in the world and serves to support local health workers through discussion and access to pertinent educational materials. Many developing nations have a dire shortage of doctors and other health resources. Therefore, affordable, easy-to-use technologies are imperative for providing care and much needed educational opportunities as well as reducing the limitations imposed by scarce resources. METHODS: To identify the current extent of the Africa Teledermatology Project and key areas for improvements, an analysis of all consultations received to date was completed. RESULT: Between February 2007 and February 2009, 345 consultations from sites in thirteen Sub-Saharan African nations were received and processed via the project website. Although a wide range of mucocutaneous conditions were seen, the most frequent diagnoses included adverse drug reactions, atopic dermatitis and eczema, cutaneous infections, psoriasis and HIV/AIDS-related cutaneous diseases. Educational materials were designed to target these conditions. CONCLUSION: This research supports the value of store-and-forward teledermatology services for facilitating access to assistance in the diagnosis and management of cutaneous disease and increasing access to educational materials. The work demonstrates the feasibility and usefulness for a teledermatology network such as the African Teldermatology Project in improving the provision of care for skin diseases in sub-Saharan Africa. Additionally, this technology can be seen as a practical and effective manner to distribute information to local health workers with the hope of significantly improving their ability to recognize, diagnose and treat cutaneous conditions.

Epithelioid sarcoma with angiomatoid features: report of an unusual case arising in an elderly patient within a burn scar.

Epithelioid sarcoma (ES) is a rare, aggressive soft tissue tumor with a characteristic predilection for adolescents and young adults, and a tendency to occur on distal extremities. We report a case of ES arising in an 80-year-old woman within a burn scar that histopathologically showed unusual 'angiomatoid' features. The patient presented initially with a solitary nodule on her right wrist arising at the site of a burn scar. Histopathologically, the tumor was composed of a proliferation of relatively bland, epithelioid and spindle cells focally arranged in a nodular pattern around areas of 'geographic' necrosis. In addition, there were prominent foci of hemorrhage and blood-filled spaces as well as tumor cells with intracytoplasmic vacuoles, features suggestive of an angiomatous process. Immunohistochemistry showed positivity of tumor cells for cytokeratins and epithelial membrane antigen (EMA) whereas all vascular markers tested were negative. The overall histopathologic features were consistent with a diagnosis of ES. Follow up showed multiple recurrences arising proximally along the right upper extremity. Our case underlines the clinical and histopathological heterogeneity of ES, emphasizing the unusual occurrence of ES with 'angiomatoid' features in the elderly. In this uncommon setting, this tumor should be especially distinguished from epithelioid hemangioendothelioma and epithelioid angiosarcoma. The significance of development of ES on a healed burn scar is uncertain, but may suggest a possible causal relationship.

Pseudolymphomatous cutaneous angiosarcoma: a rare variant of cutaneous angiosarcoma readily mistaken for cutaneous lymphoma.

Cutaneous angiosarcoma is probably the most malignant neoplasm involving the skin. Three clinical variants of cutaneous angiosarcoma are recognized, including angiosarcoma of the scalp and face of elderly patients, angiosarcoma associated with chronic lymphedema, and postirradiation angiosarcoma. Histopathologically, these three variants of angiosarcoma show similar features, which consist of poorly circumscribed, irregularly dilated, and anastomosing vascular channels lined by prominent endothelial cells that dissect through the dermis. Focally, neoplastic endothelial cells show large, hyperchromatic, and pleomorphic nuclei, protruding within vascular lumina and creating small papillations. Usually, inflammatory infiltrate is sparse and consists of a patchy, perivascular lymphoid infiltrate around the neoformed vessels. In rare instances, cutaneous angiosarcomas may exhibit prominent inflammatory infiltrate, and the neoplasm may be mistaken for an inflammatory process, both from clinical and histopathologic points of view. We describe four examples of cutaneous angiosarcomas with dense lymphocytic infiltrates involving the neoplasm. Immunohistochemically, lymphocytes expressed immunoreactivity for CD3, CD5, and CD45 markers, whereas the germinal centers were positive for CD20, CD79a, and Bcl-6. The neoplastic endothelial cells expressed immunoreactivity for the CD31, CD34, podoplanin, Prox-1, Lyve-1, and D2-40. We discuss the possible relationship between neoplastic endothelial lymphatic cells and reactive lymphocytes. Cutaneous angiosarcoma with prominent lymphocytic infiltrate may be readily mistaken for cutaneous follicle center cell lymphoma or cutaneous pseudolymphoma.

Teledermatopathology: a controlled study about diagnostic validity and technical requirements for digital transmission.

Telepathology is the practice of diagnostic histopathology performed on digital pictures. In this study, we focused on the technical requirements for achievement of a correct diagnosis on digital histopathologic images. A collection of 560 melanocytic lesions was selected from the files of the Department of Dermatology, Medical University of Graz, Austria. From each lesion one histologic slide was completely digitally scanned with a robotic microscope. Digital pictures were reviewed by 4 dermatopathologists using a presentation program, which recorded the number of image calls, applied magnifications, overall time needed, and amount of transmitted bits during the digital sign-out. One month later, the 4 microscopists had to review the corresponding slides and render a direct diagnosis on each case. Telepathologic diagnoses corresponded with the original diagnoses in a range from 90.4% to 96.4% of cases (kappa 0.80 to 0.93; P < 0.001). The median time needed for achievement of a diagnosis was 22 seconds and was significantly higher for melanomas compared with nevi. The median transmission effort for each diagnosis was 510 kilobytes after JPEG compression. Using an ISDN line with a transmission capacity of 64 kilobits/ second, this correlates to a transmission time of about 1 minute. Our results demonstrate that correct reporting on digital histopathologic images is possible with only a little time exposure. For an adequately fast transmission ISDN lines are suffcient after JPEG compression.

A distinctive type of widespread congenital melanocytic nevus with large nodules.

We report an unusual case of congenital melanocytic nevus presenting in a 19-year-old African woman as widespread papules and variably sized nodules and tumors affecting the entire body, including the palms, soles, and oral mucous membrane. Histopathologic examination of 3 representative skin lesions showed mainly dermal aggregations of round to oval, focally pigmented, monomorphous melanocytes, arranged in nodular and plexiform patterns. Scattered areas with spindle-shaped dendritic melanocytes surrounded by fibrosis were also noted in the center of the lesions. The clinical and histopathologic findings were similar to those in 2 other previously reported cases, except that in 1 of the earlier cases the skin nodules were composed of spindle-shaped cells, suggesting a type of blue nevus. The findings in our case indicate a broader spectrum of morphologic features in this condition, with dermal aggregations of melanocytes showing congenital features, representing a common histopathologic denominator. Based on this observation, we suggest the term "widespread congenital dermal nevus with large nodules" to be the most appropriate for this rare, but distinctive, type of congenital nevus.

Cutaneous myoepithelial neoplasms: clinicopathologic and immunohistochemical study of 20 cases suggesting a continuous spectrum ranging from benign mixed tumor of the skin to cutaneous myoepithelioma and myoepithelial carcinoma.

BACKGROUND: Myoepithelial neoplasms, both benign and malignant, are rare but well-established clinicopathologic entities in the salivary glands, the breast, and the lung. Despite similarities between cutaneous sweat glands and glandular structures in the above-mentioned organs as well as the presence of regular myoepithelial cells around cutaneous eccrine/apocrine glands, the concept of cutaneous myoepithelial neoplasms is still debatable and not commonly accepted. METHODS: Twenty cutaneous myoepithelial neoplasms have been studied histologically and immunohistochemically. RESULTS: Nine neoplasms showed features of benign mixed tumor of the skin (chondroid syringoma) (five females and four males, age range 19-65 years, all cases arose in the head and neck region). Two cases represented the eccrine and seven the apocrine subtype. Interestingly, in three cases of the apocrine subtype, solid areas composed predominantly of myoepithelial cells were detected; these neoplasms were designated as benign mixed tumors with prominent myoepithelial cells. Nine cutaneous neoplasms were composed of spindled, epithelioid, and plasmocytoid cells without ductal differentiation and immunohistochemically stained variably positive for vimentin, epithelial and myogenic markers, S-100 protein, calponin, and glial fibrillary acidic protein (four females and five males, age range 3-71 years, four cases arose in the head and neck region and one case each on the finger, the thigh, the lower leg, the foot, and the breast, respectively); these neoplasms were designated as cutaneous myoepitheliomas. Two morphologically malignant neoplasms with cytologic and immunohistochemical features of myoepithelial cells arose on the face of a 70-year-old female and a 79-year-old male patient; these neoplasms were designated as malignant cutaneous myoepitheliomas (cutaneous myoepithelial carcinomas). CONCLUSIONS: The study suggests a continuous spectrum of cutaneous myoepithelial neoplasms ranging from benign mixed tumor of the skin to cutaneous myoepithelioma and cutaneous myoepithelial carcinoma. Further studies with extended follow-up information are necessary to establish prognostic factors.

Loss of expression of tuberin and hamartin in tuberous sclerosis complex-associated but not in sporadic angiofibromas.

BACKGROUND: Angiofibromas occur sporadically, and they develop in most patients with tuberous sclerosis complex (TSC), which is associated with alterations of the tumor suppressor genes TSC1 or TSC2. Loss of tuberin, the protein product of TSC2, has been shown in the interstitial fibroblast compartment of TSC-associated angiofibromas. It is unclear whether there is also a loss of hamartin, the product of TSC1 in TSC-associated and sporadic angiofibromas. METHODS: The expression of hamartin and tuberin was analyzed by immunohistochemistry in 59 TSC-associated and 12 sporadic angiofibromas using affinity-purified antibodies. RESULTS: Loss of expression of both tuberin and hamartin was detected in 14 angiofibromas, loss of only tuberin in three, and loss of only hamartin in four TSC-associated angiofibromas; but there was no loss in the sporadic angiofibromas. Only the interstitial cells, but not the vascular cells, showed a loss of expression of tuberin or hamartin. CONCLUSIONS: Loss of tuberin or hamartin occurred in a minority of the TSC-linked angiofibromas, but not in the sporadic angiofibromas. The absence of both tuberin and hamartin in some of the tumors suggests that the stability of tuberin and hamartin, which are believed to form an active complex in vivo, is negatively affected by the absence of either of the partners.

Dermoscopic and histopathologic diagnosis of equivocal melanocytic skin lesions: an interdisciplinary study on 107 cases.

BACKGROUND: Dermoscopy (dermatoscopy, epiluminescence microscopy) is increasingly employed for the preoperative detection of cutaneous melanoma; dermoscopic features of pigmented skin lesions have been previously defined using histopathology as the key to the code. In a preliminary study on 10 cases evaluated by nine dermoscopists and nine histopathologists, the authors experienced that when at least two dermoscopists disagree in evaluating a melanocytic lesion, even histopathologic consultations may give equivocal results. METHODS: One hundred seven melanocytic skin lesions, consecutively excised because of equivocal clinical and/or dermoscopic features, were retrospectively examined by eight dermoscopists and eight histopathologists; the diagnostic interobserver agreement was calculated by means of the Schouten k statistics. After histopathologic consultations, all 107 lesions underwent unblinded dermoscopic re-evaluation in order to find which dermoscopic features had given rise to histopathologic diagnostic difficulties. RESULTS: The interobserver ageement was good for both dermoscopy (k = 0.53) and histopathology (k = 0.74). Out of 48 cases evaluated by the dermoscopists in complete accordance, only 8 (16.7%) received at least one conflicting histopathologic diagnosis. Instead, among the remaining 59 cases with at least one disagreeing dermoscopic diagnosis, 21 (35.6%) received at least one disagreeing histopathologic diagnosis. The unblinded dermoscopic re-evaluation showed that five out of seven lesions with clear-cut regression structures were histopathologically controversial. CONCLUSIONS: At least for selected and reasonably difficult lesions, a diagnostic discrepancy among formally trained dermoscopists seems to be predictive for a diagnostic disagreement among histopathologists. Lesions showing clear-cut regression structures are prone to give some histopathologic disagreement.

Warty dyskeratoma--"follicular dyskeratoma": analysis of clinicopathologic features of a distinctive follicular adnexal neoplasm.

BACKGROUND: The clinicopathologic spectrum of warty dyskeratoma (WD) is not well characterized and the pathogenesis of this unusual lesion is still unclear. OBJECTIVE: We reviewed the clinical and histopathologic spectrum of WD and investigated a possible involvement of human papillomavirus (HPV) infection in onset of this lesion. METHODS: A total of 46 cases of WD were analyzed clinically and histopathologically. Polymerase chain reaction (PCR) analysis for HPV-DNA was performed in 13 lesions of WD. RESULTS: A total of 46 lesions of WD from 45 patients (M/F ratio, 1:1.8; mean age 59.8 years, median 61 years, age range 3-88 years) presented as solitary papules or small nodules on the head and neck (32 cases), trunk (9 cases), lower extremities (4 cases), and upper extremities (1 case). One patient had 2 lesions. No patient had clinical signs of Darier's or Grover's disease. Histopathologically on scanning magnification, lesions showed mainly 3 architectural patterns, namely, cup-shaped (29 cases), cystic (6 cases), and nodular (2 cases). In 9 cases, a combination of two of these morphologic patterns was observed. Characteristically, the epithelial component in all WDs displayed foci of acantholytic dyskeratosis. Variable features suggestive of follicular differentiation toward the infundibular portion of a normal hair follicle were also observed, including a focal contiguity to pilosebaceous units in most cases (63%), and the presence of small infundibular cystic structures in a subset of lesions (46%). The majority of lesions (83%) also revealed a hyalinized or fibrous stroma with intrastromal clefts. PCR analysis for HPV-DNA performed in 13 cases inclusive of all representative architectural patterns was negative. CONCLUSION: We conclude that WD shows a wider spectrum of morphologic features than previously recognized. Despite some histopathologic similarities to viral warts, WD is not a manifestation of HPV infection. On the other hand, the majority of these lesions display overall histopathologic features consistent with a follicular adnexal neoplasm. On the basis of this finding, we propose the alternative term follicular dyskeratoma to better reflect the distinctive features of this peculiar lesion.

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

Atypical fibrous histiocytoma is an uncommon, poorly documented variant of cutaneous fibrous histiocytoma. We studied 59 cases of atypical fibrous histiocytoma to better characterize the clinicopathologic spectrum. There were 33 males and 26 females (median age 38 years; range 5-79 years) with solitary lesions arising on lower (25 cases) and upper (17 cases) extremities, trunk (6 cases), head and neck (4 cases), and vulva (1 case); anatomic location was not stated in six cases. Lesions measured 0.4-8 cm in diameter (median 1.5 cm) and clinically were nodules (40 cases), polypoid tumors (18 cases), or a slightly elevated plaque (1 case). Histologically, the lesions were primarily dermal with superficial involvement of the subcutis in one third of the cases. Salient features included a proliferation of pleomorphic, plump, spindle, and/or polyhedral cells with mainly large, hyperchromatic, irregular, or bizarre nuclei, set in a background of classic features of fibrous histiocytoma, including spindle cell areas showing a storiform pattern and entrapped thickened, hyaline collagen bundles, especially at the periphery. Multinucleated giant cells, often with bizarre nuclei and foamy, sometimes hemosiderin-rich, cytoplasm were also variably present. The degree of pleomorphism varied from only focal and minimal (14 cases) or moderate (24 cases) to marked (21 cases). Mitotic activity was observed in 55 lesions, and the number of mitotic figures ranged from 1 to 15 per 10 high power fields. Atypical mitoses were noted in 20 lesions. Furthermore, some cases of atypical fibrous histiocytoma displayed other worrisome features less often observed in ordinary FH, including unusually large size (diameter >2 cm, 8 cases), involvement of the superficial subcutis (19 cases), and geographic necrosis (7 cases). Immunohistochemical studies performed in 42 cases showed only focal smooth muscle actin (10 cases) and CD34 (4 cases) positivity, whereas CD68, S-100 protein, desmin, pan-keratin, and epithelial membrane antigen were negative. Clinical follow-up data available in 21 patients (mean duration of follow-up 50.6 months, median 43 months) revealed local recurrences in three patients (one repeated); two patients developed distant metastases, one of whom died after 96 months. These two cases were not histologically distinct from the group as a whole. We conclude that atypical fibrous histiocytoma has a broader clinicopathologic spectrum than previously realized. Lesions with floridly atypical features represent potential pitfalls for overinterpretation as pleomorphic sarcoma, which would appear to be inappropriate in most cases. Provided that atypical fibrous histiocytoma is treated by complete excision, a benign outcome is to be expected in most cases. However, similar to the cellular and aneurysmal variants of fibrous histiocytoma, atypical fibrous histiocytoma shows a higher tendency to recur locally than ordinary fibrous histiocytoma and may rarely metastasize.