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Desmoplastic melanoma can be difficult to diagnose and on average have a significantly higher T stage at the time of diagnosis compared with conventional melanomas. Histologically, these tumors typically consist of spindle cells in a fibrous matrix. The spindle cells may display fibroblast and/or Schwann cell-like features. In this study, we describe the features of 12 cases of desmoplastic melanoma closely simulating neurofibroma. Although the spindle cells in these tumors may be indistinguishable from those of neurofibroma, features such as prominent fibroplasia (12/12), poor lateral circumscription (8/9), diffuse infiltration of subcutaneous tissue (7/9), and lymphoid aggregates (10/12) may be helpful clues to the diagnosis. No immunohistochemical markers were reliable in distinguishing neurofibroma-like desmoplastic melanomas from neurofibroma. Clinical follow-up was available in 8 cases, of which 4 were initially misdiagnosed as benign neoplasms and given no further re-excision. All 4 of these cases recurred; 2 of which showed transformation to a more aggressive phenotype.

Pacinian neurofibroma (PNF) is a lobulated benign neural tumor with prominent structures resembling pacinian bodies. These tumors most commonly occur in areas where normal pacinian bodies are found, such as the hands and feet. Although pacinian bodies are common in the penis, no cases of penile PNF have been reported to date. We present a case of PNF on the dorsal glans penis of a 47-year-old man. The lesion presented as a single flesh-colored papule and the biopsy showed a dermal neurofibroma consisting of bland spindle cells with wavy nuclei, without mitoses or atypia, and some nodular structures with a concentric arrangement and a pacinian appearance. Immunohistochemistry demonstrated positivity for CD34 and Vimetin and negativity for Epithelial Membrane Antigen (EMA). S100 was highly positive in the most central areas of the pacinian-like nodules, while the periphery and non-nodular parts of the neurofibroma were less intensively expressed., (Copyright © 2019 Sociedad Española de Anatomía Patológica. Publicado por Elsevier España, S.L.U. All rights reserved.)

Spindle cell lipoma (SCL), also called as pleomorphic adenoma, is a rare variant of lipoma histopathologically characterized by an admixture of mature fat cells with spindle cells and occasionally mast cells with myxoid connective tissue stroma and thick bends of birefringent collagen. Although buccal mucosa is the most common location for oral lipomas, for SCL, it is an exceedingly rare location. We report a case of an asymptomatic swelling of buccal mucosa that simulated the features of neurofibroma on histopathological examination, and the final diagnosis of SCL was made on the basis of immunohistochemical features. This is the first documentation of oral SCL using SOX10 to achieve the final diagnosis., Competing Interests: There is no conflict of interest

Distinguishing desmoplastic melanomas (DMs) from neurofibromas (NFs) can be histologically challenging in some cases. To date, a reliable marker to differentiate the 2 entities has remained elusive. S100 subtyping and CD34 fingerprinting have been proposed, but controversy remains as to their reliability. Missense mutations in TP53 are often found in DMs, resulting in a dominant negative effect and paradoxical accumulation of the tumor suppressor protein p53. We hypothesized that p53 may be expressed differentially in DMs, making it a valuable tool in differentiating DMs from NFs. Using immunohistochemistry, we compared p53 protein expression in 20 DMs and 20 NFs retrieved from our tissue archives and stained with p53 antibody (Monoclonal, DO-7). Patients with DM included 18 men and 2 women (age, 36 to 95 y; mean, 70.5 y; median, 70 y). Fifteen (15/20) tumors occurred in head and neck area; 2 (2/20) on the trunk; and 3 (3/20) on the extremities. Patients with NF included 12 men and 8 women (age, 47 to 85 y; mean, 65.2 y; median, 69.5 y). Eleven (11/20) tumors occurred on the trunk, 6 (6/20) on the extremities, and 3 (3/20) on the head and neck area. A total of 19/20 (95%) DMs were positive for p53. DM Histo-scores ranged from 0 to 300 (mean, 203; median, 260). Nuclear accumulation of p53 was seen in all 19 positive DMs. None of the 20 NFs were positive for p53 (2-tailed t test P-value <0.0001). Detection of p53 by immunohistochemistry can help to distinguish DMs from NFs.

Benign and malignant peripheral nerve sheath tumors can involve the breast, presenting as masses in the dermis, deep breast parenchyma or axillary soft tissue. Although the histologic features are frequently characteristic, diagnosis can be challenging on core needle biopsy, and the differential diagnosis includes a variety of other benign and malignant spindle cell lesions of the breast. Here, we review the key clinical and pathological features of breast schwannoma, neurofibroma, granular cell tumor, and malignant peripheral nerve sheath tumor., (Copyright © 2017 Elsevier Inc. All rights reserved.)

A pregnant patient presented with symptomatic ventricular tachycardia. Echocardiography revealed a large intramyocardial mass. Surgical resection was attempted in conjunction with cryoablation of the surrounding myocardial tissue. Histologic examination of the resected mass revealed cardiac neurofibroma. To the best of our knowledge, this is the first report of cardiac neurofibroma in a pregnant patient in the absence of any neurocutaneous syndromes such as neurofibromatosis., (Copyright © 2016 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Development of malignant peripheral nerve sheath tumors (MPNSTs) is a stepwise process that involves the alteration of many cell cycle regulators and the double inactivation of the NF1 gene. Inactivation of the TP53 gene and deletion of the CDKN2A/p16 gene are known to play an important role in the process. Herein, we present a 19-year-old man with a familial history of neurofibromatosis type 1, in whom the tumor arose from the intercostal nerve and showed 3 components: a neurofibroma, a low-grade MPNST, and a high-grade MPNST. Loss of p16 expression and homozygous deletion of the CDKN2A/p16 gene were observed in both the low-grade and the high-grade MPNST. In contrast to low-grade MPNSTs, high-grade MPNSTs generally tend to lose expression of p16 and harbor homozygous deletion of the CDKN2A/p16 gene. Loss of p16 expression and homozygous deletion of the CDKN2A/p16 gene in low-grade MPNST in our case might be related to its progression to high-grade MPNST. To the best of our knowledge, this is the first study correlating the p16 expression status and CDKN2A/p16 gene alteration in low-grade MPNSTs.

Background: Synovial sarcoma is a mesenchymal neoplasm that accounts for around 10% of all soft tissue sarcomas. The diagnosis of synovial sarcoma can be a challenging task, particularly with small biopsy specimens., Aim: We investigated transducer-like enhancer of split 1 (TLE1), monoclonal antibody, expression by immunohistochemical analysis in a group of 74 synovial sarcoma cases, 20 cases of MPNST, 12 cases of neurofibroma, 15 cases of schwannoma, 5 cases of MFH, 10 cases of lieomyosarcoma and 10 cases of solitary fibrous tumor., Materials and Methods: Whole tissue sections were examined: (39 biphasic and 35 monophasic). Nuclear immunoreactivity was scored as negative (<5% of cells positive), 1+(mild /5-25%), 2+ (moderate/25-50%), and 3+ (strong >50%)., Results: Overall, 71 (96%) of 74 synovial sarcomas were positive for TLE1, including 37 biphasic (95%) and 34 monophasic (97%) tumors. Other spindle cell tumors showed very low or absent staining of TLE1., Conclusions: We conclude that TLE1 is a sensitive marker and can be a useful diagnostic marker for synovial sarcoma, particularly the monophasic forms.

Aims: To report a rare case of isolated diffuse episcleral neurofibroma and to discuss possible differential diagnoses., Case Report: A 37 year old Caucasian female was found to have an epibulbar tumour arising from the superior aspect of her left eye. Clinical examination revealed a 12 mm × 8 mm "salmon pink" coloured lesion., Results: A biopsy was performed and histopathologic examination and subsequent systemic evaluation showed it to be a rare case of isolated diffuse episcleral neurofibroma., Conclusion: There are many differential diagnoses for an epibulbar lesion and neurofibroma should be added to these. Even though a small risk of malignant transformation exists, we recommend a conservative approach for slow growing lesions.

The tumor suppressor disorder neurofibromatosis type 1 (NF1) is associated with development of multiple neurofibromas which may grow intraneurally as plexiform neurofibromas (PNF) or intracutaneously (CNF). Upon surgery neurofibromas may show prominent swelling hindering skin-edge approximation. To assess whether the water binding glycosaminoglycan hyaluronan is involved in intra-operative swelling, 51 neurofibromas from 33 NF1-patients were investigated. Hyaluronan was histologically demonstrated and was quantified by ELISA. Molecular weight of hyaluronan was determined by gel filtration. Further, hyaluronan content was measured in cultivated Schwann cells and fibroblasts. Clinically, 67% of PNF were associated with moderate or severe intra-operative swelling, whereas only 36% of CNF showed this feature. Significantly higher levels of hyaluronan content were found in PNF compared to CNF (P < 0.05). Mast cell density did not correlate with any of the parameters. Molecular weight of hyaluronan in PNF and CNF ranged from higher than 10⁶ Da to approximately 10⁵ Da. Fibroblasts produced less hyaluronan than Schwann cells. The findings support the view that hyaluronan plays an important role in intra-operative swelling in neurofibroma surgery., (© 2011 Japanese Society of Neuropathology.)

Unlabelled: Neurofibromas are benign nerve sheath tumours. They occur sporadically, singly or few in number, and in neurofibromatosis type 1 (NF1), an autosomal inherited disease. These tumours are composed of different cell types, e.g. nerve cells (axons and axon sheaths), Schwann cells, mast cells, and fibroblasts. The local control of tumour growth in NF1 is poorly understood. Identification of cell markers could provide new information on the processes that are involved in tumour growth., Materials and Methods: NF1 patients were diagnosed according to the revised NF1 diagnostic criteria proposed by the US National Institute of Health. Fifteen cutaneous neurofibromas from eight patients (origin: trunk and face) were excised, immediately immersion-fixed in Bouin's fixative and embedded in paraffin. Six micrometre thin sections were incubated with a variety of neuronal markers, connective tissue and glial cell markers, neurotrophic factors and their receptors. In addition, material was fixed, embedded and further processed for light and electron microscopic studies., Results: The tumours were composed of different cell types, e.g. nerve cells (axons and axon sheaths), Schwann cells, mast cells, compartmentalising cells and fibroblasts. Neuronal markers were identified in axons (neuron-specific protein gene product 9.5, PGP9.5), in several cell types (neurofilament protein-200 kDa, NF-200) and glial cells (protein S-100, S-100). In glial cells the immunoreactivity for fibroblast surface protein (FSP) was scanty, low for cyclic 2,3-nucleotide 3'-phosphodiesterase (CNPase), strong for glucose transporter 1 (Glut-1) but lacking for glial fibrillary acidic protein (GFAP). Schwann cells and so-called compartmentalising cells exhibited immunoreactivity for neurotrophin receptor protein TrkA (TrkA) and glial cell-derived neurotrophic factor (GDNF). GDNF receptor α-1 (GFR-α1) exhibited distinct immunoreactivity in single axons, in Schwann cells, and with lower intensity in some perineurial sheet cells. No immunoreactivity was observed for the low-affinity neurotrophin receptor protein p75(NTR), high-affinity receptor protein TrkB (TrkB), high-affinity receptor protein TrkC (TrkC), the neurotrophin 3 (NT-3), and the brain-derived neurotrophic factor (BDNF)., Conclusion: Human cutaneous neurofibromas displayed a pattern of neurotrophic factors and their receptor immunoreactivity, which is characteristic of differentiated non-malignant tumours, and exhibited some differences from that established in developing and differentiated control Schwann cells (probably involved in the pathogenesis of the neurofibromas), as well as tumour cells in the process of differentiation. Neurofibromas are highly vascularized tumours and possess activated endothelial cells and pericytes. We presume that most of the hyperplastic structural components of a neurofibroma are generated from activated pericytes and smooth muscle cells of the small tumour vessels which possess qualities of adult stem cells.

Intrapulmonary neurofibromas without neurofibromatosis type 1 are rare-so rare that only 11 cases have been reported previously. This case report describes a 37-year-old woman who was otherwise healthy. Chest radiography and computed tomography showed a solitary nodule, 20 mm diameter, in the left lung. The tumor was removed and examined. It was not encapsulated but was covered with an intact bronchial mucosa and lacked a clear partition into two areas of Antoni A (a palisading cellular component) and Antoni B (a loose myxoid component). Tumor cells were strongly positive for neuron-specific enolase and S-100 protein. These data characterized the tumor as a rare benign neurofibroma. The patient shows no sign of recurrence after 12 months of follow-up. We reviewed and characterized surgically resected cases of intrapulmonary neurofibroma without neurofibromatosis type 1 especially in comparison with cases of endotracheobronchial neurofibroma.

Background: Oral neurofibromas are peripheral nerve sheath tumors, similar to schwannomas. Histological variations in oral neurofibromas are relatively uncommon., Case Presentation: Here, we present a case of unique variation in the observed characteristics of a neurofibroma, with no relation to neurofibromatosis type-1 or von Recklinghausen disease of the skin. The neurofibroma was observed in the right mandibular gingiva of a 32-year-old Japanese woman. Histologically, it differed from conventional neurofibromas in that the tumor was composed of a mixture of fine fibrillary collagen in sheets and/or cords of neoplastic Schwann cells containing numerous clusters of Meissner bodies. Histologically, these bodies were in contact with neoplastic Schwann cells. The Meissner bodies were immunopositive for S-100 protein, neuron-specific enolase, and vimentin, but were negative for calretinin. CD34-positive spindle cells were observed around the Meissner bodies. No recurrence or signs of other tumors have been observed in the patient for 5 years after tumor resection., Conclusion: To the best of our knowledge, no formal descriptions of sporadic, solitary neurofibromas containing numerous Meissner bodies occurring in the oral cavity are available in literature. We believe that an uncommon proliferation of Meissner bodies, as seen in the present case, may result from aberrant differentiation of neoplastic Schwann cells.

It is difficult to differentiate some malignant peripheral nerve sheath tumors (MPNST) from benign peripheral nerve sheath tumors (BPNST) histologically, and to predict the clinical outcome of patients with MPNST. In this study, the expression of VEGF and MVD were evaluated immunohistochemically in 22 cases of MPNST, 14 of neurofibroma and 19 of schwannoma and correlation of the staining grade of VEGF or MVD and the various clinical factors were analyzed, and statistically evaluated. Levels of VEGF mRNA expression were also determined with real-time RT-PCR. Statistically higher positive staining for VEGF was observed in MPNST compared to neurofibroma (P=0.004) and schwannoma (P<0.001). Even low grade MPNST showed higher VEGF positive staining than neurofibroma. Moreover, high VEGF expression statistically correlated with the poor prognosis of the patients with MPNST (P=0.015). Although MVD in MPNST was significantly higher than that in neurofibroma (P=0.038) and schwannoma (P<0.001), MVD could not predict the prognosis of the patients with MPNST. Although VEGF mRNA expression tended to be higher in MPNST compared to neurofibroma, the difference was not significant. Levels of VEGF protein expression serve as a novel diagnostic and prognostic tools for peripheral nerve sheath tumors.

Schwannomas are benign peripheral nerve sheath tumors believed to be composed purely of cells with ultrastructural features of Schwann cells; these tumors are believed to develop eccentrically from the surface of nerves and not to contain axons, other than immediately beneath the capsule. This concept has recently been disputed in cases associated with neurofibromatosis type 2. The usual presence of intratumoral axons in neurofibromas is said to allow easy distinction from schwannomas. Eighty sporadic schwannomas (20 conventional, 20 cellular, 20 ancient, 10 gastric, and 10 plexiform) were retrieved from the authors' files. Hematoxylin-and-eosin stained slides were reviewed, diagnoses were confirmed and all tumors were stained for S-100 protein and neurofilament protein (NFP). The amount (rare, focal, multifocal, and diffuse) and distribution (central and/or peripheral) of axons within the tumors were analyzed. All tumors were strongly and diffusely positive for S-100 protein (nuclear and cytoplasmic staining). NFP-positive axons were identified in 11 of 20 (55%) conventional schwannomas (2 rare, 4 focal, 3 multifocal, and 2 diffuse; 5 central, 4 peripheral, and 2 central and peripheral) and in 15 of 20 (75%) cellular schwannomas (3 rare, 6 focal, and 6 multifocal; 12 central, 1 peripheral, and 2 central and peripheral). Of the 20 ancient schwannomas, 7 cases (35%) showed intratumoral axons, highlighted by NFP immunostaining (1 rare, 4 focal, 1 multifocal, and 1 diffuse; 4 peripheral, 2 central, and 1 central and peripheral). Most cases of gastric schwannoma showed no evidence of intratumoral axons; 9 cases (90%) were negative for NFP and only 1 case (10%) was positive (focal and central). Seven of 10 cases (70%) of plexiform schwannomas were negative for NFP, whereas only 3 cases (30%) showed positive axons (2 multifocal and 1 focal; 3 central). The unexpected but quite frequent presence of intratumoral axons in schwannomas argues against conventional views of these lesions' pathogenesis as an eccentric encapsulated lesion and raises the possibility that a more diverse cell population, perhaps more closely resembling neurofibromas, may constitute these neoplasms. Although NFP-positive axons were most often present in the conventional and cellular variants of schwannoma, their presence was also observed in a minority of ancient, gastric and plexiform schwannomas. Differentiation between neurofibroma and schwannoma in cases with overlapping cytoarchitectural features should not be based solely on the presence or absence of NFP-positive axons within a given tumor.

A case of two sporadic cellular neurofibromas with atypia and one widespread hyalinization neurofibroma of the lumbar spine in a 51-year-old man without evidence of neurofibromatosis-1 is reported. Cellular neurofibroma with atypia is an unusual variant. The definite criteria for low-grade and high-grade malignant peripheral nerve sheath tumors as well as cellular neurofibroma are not well defined in the literature. The clinical significance of atypical cellular neurofibroma has rarely been systematically studied. To our knowledge, the concomitance of cellular architecture and cytologic atypia is rarely documented, and this is a rare report of atypical cellular neurofibroma. The recognition of this entity is of great importance to both pathologists and clinicians because atypical cellular neurofibroma is clever at masquerading both histologically and cytologically as a sarcoma; therefore, a precise diagnosis of this variant is essential because of the differences in treatment and clinical behavior between benignancy and malignancy. We also examined the immunohistochemical characteristics of CD34 positive cells and focal high expression of p53 up to 73% encountered in our case. To our knowledge, seldom have series or case reports elucidated this phenomenon.

Background: Neurofibroma (NF) is a benign tumor of the nerve sheath. Several variants of NF have been described., Purpose: We report a case of NF with sclerotic changes resembling sclerotic fibroma (SF)., Methods and Results: The patient was a 61-year-old man who had an asymptomatic cutaneous lesion on the right scapular region. Physical examination revealed a pedunculated, white-to-pinkish nodule that had a firm consistency, spherical morphology, and smooth surface. Microscopically, the nodule showed a well-circumscribed, nonencapsulated dermal tumor composed of scant cells and thick collagen bundles with prominent clefts. The tumor cells were immunoreactive for vimentin and S100 protein. The patient was diagnosed as having pure sclerotic NF. To our knowledge, only five cases of NF with SF-like pattern have been previously published, and in two this pattern was pure., Conclusion: It is important to recognize this exceptional type of NF because it may be easily confused with SF, as well as with a wide variety of neoplasms or hamartomatous conditions containing similar sclerotic pattern.

Spindle cell proliferations of the urinary bladder are uncommon but may cause significant diagnostic difficulty resulting from the degree of morphologic overlap between clinically benign and malignant lesions. These difficulties may be amplified in small biopsies because some of the more specific diagnostic features may not be present for evaluation. In addition, the number of different diagnostic terms applied to the same entity has added confusion to this diagnostic area. This review discusses the nomenclature, morphologic criteria, and immunohistochemical features used to classify spindle cell proliferations occurring in the urinary bladder, including those with myofibroblastic, smooth muscle, skeletal muscle, epithelial (sarcomatoid urothelial carcinoma), fibroblastic, and neural differentiation. A separate discussion of 5 challenging differential diagnostic scenarios is also presented.

Background: There are numerous variants of cutaneous neurofibroma reflecting its manner of growth and histologic composition. Lipomatous neurofibroma is the latest described variant with only eight cases reported., Methods: A systematic study based on 320 consecutive specimens diagnosed of cutaneous neurofibroma was carried out. Conventional microscopy, immunohistochemistry, and statistical methods were used to determine the presence of fat cells, their amount, distribution, and frequency., Results: Intratumoral fat was observed in 22 (6.9%) neurofibromas. All these were dermal neurofibromas. Intraneoplastic fat was divided into two groups: focal and diffuse (regularly interspersed). Eighteen tumors (5.6%) presented adipocytes focally intermingled with the spindle cells. There were four (1.3%) neurofibromas showing spindle cell proliferation with regularly scattered adipocytes. Lipomatous neurofibroma was more frequent located on head and neck than non-lipomatous neurofibroma ( p = 0.04). Neurofibromas without mature adipocytes were more frequently immunoreactive for CD34 compared with tumors showing intratumoral fat ( p = 0.02)., Conclusions: We suggest that both metaplasia and aberrant adipose differentiation from multipotential cells may result in lipomatous neurofibroma. Focal presence of adipose cells may be attributable to metaplasia as the pathogenic mechanism. The fatty tissue being intrinsic to the tumor structure in its diffuse form, the lesion represents a distinctive tumor of the peripheral nerve sheath.

We present three cases of subcutaneous tumors with hybrid features of schwannoma-perineurioma (one case) and neurofibroma-perineurioma (two cases), which occurred in two women aged 50 and 52 years and one man aged 52. Locations included the scapular area, skin overlying breast and knee area. The tumors were 1.5, 4 and 5 cm in largest diameter. None of the patients had signs of neurofibromatosis. All tumors were surgically removed, and patients remained disease-free for 1 to 4 years. The classification of the lesion into schwannoma-perineurioma and neurofibroma-perineurioma rested on histopathological and immunohistochemical findings. An ultrastructural study was performed in one case of neurofibroma-perineurioma. All cases were studied for mutation of the NF2 gene, and in one case (neurofibroma-perineurioma) a point mutation was detected in exon 15 of the gene.

We studied 25 cases of schwannoma and 42 cases of neurofibroma immunohistochemically with antibodies to calretinin and S-100 protein to explore the potential usefulness of calretinin in differentiating schwannomas from neurofibromas. Of 25 schwannomas, 24 (96%) showed moderate to strong staining for calretinin, with the extent of staining ranging from focal to diffuse. In contrast, only 3 (7%) of 42 neurofibromas displayed focal weak to moderate staining with calretinin. All 42 cases of neurofibromas and all 25 cases of schwannomas showed diffuse moderate to strong staining with S-100 protein. Calretinin also labeled mast cells, whose presence was confirmed further by staining for c-kit, which commonly was present in both tumor types in a scattered individual cell pattern easily differentiated from the clustered pattern of neoplastic spindle cells. Taken together, these results indicate that calretinin is detected in almost all schwannomas and in only a small percentage of neurofibromas, suggesting it is a useful marker for differentiating schwannomas from neurofibromas. Although mast cells present in these 2 neoplasms also react with calretinin, the pattern of staining can be distinguished easily from that of neoplastic cells.

Gastrointestinal schwannoma (GIS) is a distinctive and extremely rare lesion showing some differences from conventional soft tissue schwannoma and some similarities with common soft tissue neurofibroma. Soft tissue neurofibromas and schwannomas differ by contents of specific types of nerve sheath cells, such as Schwann cells, perineurial cells and CD34+ cells. To compare GIS with these soft tissue lesions, eight cases of typical GIS were studied immunohistochemically to evaluate their nerve sheath cell types. Epithelial membrane antigen (EMA) and claudin-1 as perineurial cell markers, and neurofilament protein as a marker for intratumoral axons were used. In addition, the tumors were stained for cytokeratin, CD117 (C-KIT), alpha-muscle specific actin, S100 protein and CD34. EMA- and claudin-positive cells were seen in 2 (25%) and one lesion, respectively, thus resembling cellular composition of neurofibroma. Intratumoral neurofilament protein positive axons otherwise typical of neurofibroma were found inside 4 tumors (50%). CD34 positivity was found in 6 tumors (75%) and often revealed a diffuse pattern as seen in neurofibroma and not a zonal pattern as described in schwannomas. These results show that GIS has some features that are more typical for neurofibroma than for conventional schwannoma. In surgical pathology practice, a finding of intratumoral axons and positivity for claudin-1 and especially for EMA should not preclude diagnosis of GIS.

Dendritic cell neurofibroma with pseudorosettes (DCNWPR) is a recently proposed variant of neurofibroma. However, its peripheral nerve sheath origin has subsequently been questioned, and it has been suggested that the neoplasm could represent a hitherto undescribed variant of melanocytic nevus with neural differentiation. Here we report a case of DCNWPR that arose almost exclusively within the confinement of the perineurium in the skin. This observation gives further evidence that this entity is a peripheral nerve sheath tumor and is unrelated to melanocytic neoplasms.

Background: The hallmark of neurofibromatosis type 1 (NF1) is the development of multiple neurofibromas. Solitary neurofibroma may occur in an individual who does not have NF1, but multiple neurofibromas tend to develop only in those with NF1. It has been suggested that hormones may influence the neurofibromas of patients with NF1. The evidence that hormones may influence the growth of neurofibromas comes mainly from the observation that localised neurofibromas of patients with NF1 commonly grow during puberty and pregnancy. Because growth hormone (GH) concentrations increase during puberty, it is possible that GH influences the growth of these tumours., Aims: To investigate the presence of GH receptors (GHRs) in neurofibromas., Methods: By means of immunohistochemistry, the presence of GHRs was investigated in two groups of patients: 16 patients without NF1 with solitary neurofibromas (group A) and 10 patients with NF1 with localised neurofibromas (group B)., Results: Six of the 16 patients in group A had neurofibromas that were immunopositive for GHR, whereas nine of the 10 patients in group B were immunopositive., Conclusions: Most patients with NF1 have localised neurofibromas that express GHR. This suggests that GH may play some role in the development of localised neurofibromas in patients with NF1.

Three cases of a solitary neurofibroma showing focal fatty changes are reported. Fatty changes in a neurofibroma are rarely observed and have not been reported, and also, the pathogenesis of neurofibroma has not been clarified. We postulate that the fatty changes in a neurofibroma may be the result of so-called senescent change or chronic injury. The origin of adipose cells may be attributable to fatty infiltration from abutting tissues or to a metaplasia of tumor cells or resident fibroblasts.

In the spectrum of neurofibromas, pigmented tumors are rare variants usually showing only faint, macroscopically obvious pigmentation. We report a case of a huge pigmented neurofibroma with extended, macroscopically striking pigmentation in a patient with stigmata of neurofibromatosis. The immunohistochemical and ultrastructural findings support a melanotic line of differentiation besides schwann cell differentiation and indicate a phenotypic neoplastic spectrum between tumorous schwann cells and melanocytes. Using comparative genomic hybridization, striking chromosomal aberrations were not detected. High level amplifications of the known chromosomal regions, including genes of major enzymes responsible for melanin synthesis, appear to be unlikely. However, smaller chromosomal defects might have been overlooked by the limited resolution of this screening method. Therefore, other mechanisms up-regulating melanogenesis, such as mutations in regulatory genes, have to be considered.

Two cases of pigmented neurofibroma of the skin are reported. In case 1, the tumor was removed from the back of a 55-year-old man with no associated neurofibromatosis. In case 2, the tumor was removed from the abdominal wall of a 21-year-old woman with neurofibromatosis. Both tumors consisted of benign, short spindle cells and multiple foci of scattered melanin-laden cells. In case 1, the spindle cells were arranged in a storiform pattern, resembling features of dermatofibrosarcoma protuberans. Immunohistochemically, the spindle cells of both cases were demonstrated to be positive for S-100 protein and CD34. The melanin-laden cells stained positively for HMB-45. This report describes an additional two cases of pigmented neurofibroma that conform to the new diagnostic criteria for this disease.

Desmoplastic/spindle cell melanoma is a rare variant of melanoma. A number of factors complicate the diagnosis of desmoplastic/spindle cell melanoma, including the variable absence of a lentiginous component, its spindle cell morphology, and its many morphologic mimics, including scars, malignant peripheral nerve sheath tumor, neurofibroma, atypical fibroxanthoma, and spindled carcinoma. The immunohistochemical confirmation of desmoplastic/spindle cell melanoma may also be difficult, because the majority of tumors are negative for specific melanocytic markers such as HMB-45 and Melan-A, despite their usual expression of S-100 protein. Two new and potentially promising melanocytic markers, microphthalmia transcription factor (MiTF) and melanoma cell adhesion molecule (Mel-CAM), have been shown to be sensitive markers of epithelioid melanoma, but have not been tested in desmoplastic/spindle cell melanoma or in other rare melanocytic neuroectodermal tumors such as clear cell sarcoma. We immunostained 79 tumors (20 desmoplastic/spindle cell melanomas, 10 scars, 10 neurofibromas, 12 malignant peripheral nerve sheath tumors, 10 atypical fibroxanthomas, 10 clear cell sarcomas, 3 melanotic schwannomas, and 4 cellular blue nevi) for MiTF and Mel-CAM. MiTF expression was seen in 11 of 20 desmoplastic/spindle cell melanomas, 0 of 10 scars, 2 of 10 neurofibromas, 0 of 12 malignant peripheral nerve sheath tumors, 1 of 10 atypical fibroxanthomas, 7 of 10 clear cell sarcomas, 3 of 3 melanotic schwannomas, and 3 of 4 cellular blue nevi. Mel-CAM expression was present in 14 of 17 desmoplastic/spindle cell melanomas, 0 of 10 scars, 4 of 10 neurofibromas, 3 of 11 malignant peripheral nerve sheath tumors, 0 of 10 atypical fibroxanthomas, 9 of 10 clear cell sarcomas, 3 of 3 melanotic schwannomas, and 0 of 4 cellular blue nevi. MiTF and Mel-CAM were coexpressed in 6 of 17 desmoplastic/spindle cell melanomas and in no other tumor. Regarding desmoplastic/spindle cell melanoma, scar, neurofibroma, malignant peripheral nerve sheath tumor, and atypical fibroxanthoma, the sensitivity and specificity of MiTF for desmoplastic/spindle cell melanoma were 55% and 91%, respectively. For this same group of tumors, Mel-CAM had a sensitivity of 82% and a specificity of 83%. We conclude that the sensitivity and specificity of MiTF for desmoplastic melanoma equals or exceeds that of such markers as HMB-45 or Melan-A, and that MiTF should be part of the initial immunohistochemical panel for the work-up of such cases. Mel-CAM, while very sensitive, is relatively nonspecific, because it is also expressed in a variety of mesenchymal tumors and carcinomas. Mel-CAM is best reserved for cases morphologically suspected to be desmoplastic/ spindle cell melanoma, in which S-100 is positive and MiTF and other melanocytic markers are negative. These markers may also be helpful in certain other differential diagnoses, such as distinguishing clear cell sarcomas from epithelioid malignant peripheral nerve sheath tumors.

Among 99 cases of neurofibroma (NF), eight tumors (8%) contained epithelial membrane antigen (EMA)-positive perineurial cells inside the lesions. These cells were numerous and represented a significant part of the tumor cell population. In case 7, EMA-positive cells represented approximately half of the tumor. These patients' ages ranged from 23 to 73 years (average 51 years). Six patients were females and two were males. Neurofibromatosis type 1 was present in one case. The histological types of neurofibromas with EMA-positive cells were as follows: cutaneous, well-circumscribed, localized type in four cases; cutaneous diffuse type in one case; subcutaneous, well-circumscribed type in two cases; and subcutaneous plexiform type in one case. Perineurial cell differentiation was suspected by examining routinely stained sections in four cases; it was unsuspected in four cases. The perineurial cells were arranged in a pattern similar to that of "pure" perineurioma. They possessed thin bipolar processes and were arranged in laminar fascicles and whorls. In cellular areas, the cytoplasm was more eosinophilic and cell borders were poorly visible. In contrast, when the stroma was myxoid, it accentuated the shape of individual cells. As these morphological features of perineurial cell differentiation in NF are not entirely specific, EMA staining is recommended to prove the perineurial cell differentiation in neurofibromas. An additional immunohistochemical result of this study is the presence of numerous CD34-positive cells in all neurofibromas, which is similar to previous studies.

Neurofibromatosis type 1 (NF1) is a common genetic disorder characterized by multiple neurofibromas, peripheral nerve tumors containing mainly Schwann cells and fibroblasts. The NF1 gene encodes neurofibromin, a tumor suppressor postulated to function in part as a Ras GTPase-activating protein. The roles of different cell types and of elevated Ras-GTP in neurofibroma formation are unclear. To determine which neurofibroma cell type has altered Ras-GTP regulation, we developed an immunocytochemical assay for active, GTP-bound Ras. In NIH 3T3 cells, the assay detected overexpressed, constitutively activated K-, N-, and Ha-Ras and insulin-induced endogenous Ras-GTP. In dissociated neurofibroma cells from NF1 patients, Ras-GTP was elevated in Schwann cells but not fibroblasts. Twelve to 62% of tumor Schwann cells showed elevated Ras-GTP, unexpectedly revealing neurofibroma Schwann cell heterogeneity. Increased basal Ras-GTP did not correlate with increased cell proliferation. Normal human Schwann cells, however, did not demonstrate elevated basal Ras activity. Furthermore, compared with cells from wild type littermates, Ras-GTP was elevated in all mouse Nf1(-/-) Schwann cells but never in Nf1(-/-) mouse fibroblasts. Our results indicate that Ras activity is detectably increased in only some neurofibroma Schwann cells and suggest that neurofibromin is not an essential regulator of Ras activity in fibroblasts.

Background: Neurofibroma of the urinary bladder is rare. Only isolated case reports have appeared. Information regarding the long term follow-up of patients with neurofibroma is limited., Methods: The authors studied 4 cases of neurofibroma of the bladder diagnosed at Mayo Clinic from 1965 through 1990. Immunostains for S-100 protein, neurofilament protein, epithelial membrane antigen (EMA), cytokeratin (CAM 5.2; AE 1/3), Type IV collagen, MIB-1, and p53 protein were performed in all cases, as was Alcian blue at pH 2.5. The mean follow-up was 9.6 years (range, 2-18 years)., Results: The mean age at diagnosis was 17 years (range, 7-28 years); the male-to-female ratio was 1:1. All four patients exhibited physical stigmata of neurofibromatosis type 1. Clinical presentations included hematuria (one patient), irritative symptoms (two patients), and pelvic mass (one patient). Long term urinary complications included bladder atony (two patients), neurogenic bladder (one patient), and recurrent urinary tract infection with hematuria (one patient). Subsequently, two patients underwent partial cystectomy and one a complete cystectomy. Involvement of the bladder was generalized in all four cases. Three tumors were transmural, showing a diffuse and plexiform pattern of growth; in the fourth case, a superficial biopsy showed only diffuse submucosal growth with conspicuous pseudo-Meissnerian corpuscle formation. An Alcian blue positive, variably collagenized matrix was present in all cases. Tumor cells displayed immunoreactivity for S-100 protein and Type IV collagen in all cases. Neurofilament protein positive axons were evident in three cases; all other immunostains were negative. The mean MIB-1 labeling index was 3.2% (range, 0.9-7.3%). No malignant transformation was observed during a mean follow-up of 9.6 years., Conclusions: Neurofibroma of the bladder presents early in life, is of the plexiform type with a diffuse component, and usually occurs in the setting of generalized neurofibromatosis type 1 rather than as isolated visceral neurofibromatosis. Malignant transformation did not occur in any of these 4 patients during a mean follow-up time of 9.6 years.

The cytomorphologic features of 13 neural lesions sampled by fine-needle aspiration (FNA) are reviewed. The frequencies at which various architectural features including Verocay bodies, filamentous background, and vascular arcades were present was recorded, along with the frequencies of cytologic findings including the presence of spindle cells, wavy nuclei, intranuclear inclusions, fishhook nuclei, nuclear pleomorphism, filamentous cytoplasm, and mitotic figures. Verocay bodies were a rare finding, present in only 1 of 11 cases. Vascular arcades were similarly infrequent (1/11 cases). Spindle-shaped cells along with wavy nuclei were the most frequent findings, with fishhook-shaped nuclei and a filamentous background of high frequency (9/11 cases). Our study indicates that some of the characteristic features recorded in the literature are rarely seen in needle aspiration smears, but features such as spindle-shaped cells, wavy and fishhook-shaped nuclei, and a filamentous background are relatively frequent findings.

Background: A common misperception is that the vascularity of a tumor can be determined by its gross appearance. Neurofibromas are grossly white in appearance. The degree of vascularity of neurofibromas has not been determined., Objective: The purpose of this study was to determine the extent of neovascularization of neurofibromas., Methods: Neurofibromas from patients with neurofibromatosis-1 or spontaneous neurofibromas were stained with antibodies against von Willebrand factor (factor VIII-related antigen) and vascular endothelial growth factor (VEGF)., Results: Neurofibromas, both spontaneous and congenital, exhibit a high degree of vascularity. In addition, perivascular cells in neurofibromas stain with antibodies to VEGF, an angiogenic factor., Conclusion: Neurofibromas, despite their gross appearance, are highly vascular. Their vascularity may be mediated, in part, through the angiogenic factor VEGF.

Aims: To characterize and delineate a subset of rare nerve sheath tumours showing hybrid features of neurofibroma and schwannoma., Methods and Results: Nine lesions were identified in the authors' files showing predominant features of neurofibroma with distinct, often nodular regions of classical schwannomatous differentiation. Most patients were adults, eight out of nine were male. Of the nine lesions, two were dermal, two were subcutaneous and five were subfascial. Five lesions had a plexiform architecture and one patient had overt neurofibromatosis. One out of six patients with follow-up developed local recurrence. Schwannoma-like regions displayed strong S100 staining, in contrast to more varied and limited S100 reactivity in neurofibromatous areas. The Antoni A areas could be quite cellular with high MIB-1 proliferation indices. No lesion underwent malignant change., Conclusions: Our results demonstrate that some nerve sheath tumours may contain histologically clear components of both neurofibroma and schwannoma, suggesting that (despite evident and well-defined clinicopathological differences) these two lesions may be even more closely related than previously recognized. Whether this phenomenon results from a localized microenvironmental change or from a clonal genetic alteration remains unknown.

Hepatocyte growth factor (HGF), secreted by mesenchymal cells, has pleiotropic biological activities on several cell types. HGF and its receptor, the c-met proto-oncogene product (c-MET) have been implicated in the genesis and progression of several carcinomas and sarcomas. It has been suggested that MET/HGF autocrine signaling may contribute to tumorigenesis in sarcomas. HGF has been recently found to be a mitogen for rat Schwann cells and to be present in neurofibromas in NF1 patients. In this investigation, we assessed the immunoreactive patterns of HGF and MET in benign and malignant peripheral nerve sheath tumors (PNST) using archival formalin-fixed tissue. The standard avidin-biotin-peroxidase method was used. All benign tumors were negative with HGF. Eight cases of MPNST were positive with both HGF and MET. In some malignant PNST, positivity with both ligand and the receptor may be indicative of an autocrine mediated signal transduction and may implicate HGF/MET in tumor progression. Immunoreactivity with MET was strikingly greater in MPNST in contrast to benign PNST; this finding may prove to be helpful in distinguishing some histologically low-grade MPNST from cellular and atypical benign PNST.

The monoclonal antibody CD 68 (KP 1) reacts with fibrohistiocytic and some epithelial neoplasms; its reactivity compared with that of HMB 45 in malignant melanoma (MM) and neural tumors needs further elucidation. Using a streptavidin-biotin-immunoperoxidase procedure, we examined the reactivity of 65 MM (46 conventional, 1 polypoid, 6 desmoplastic [DMM], and 12 metastatic), 21 neurofibromas, 1 neurofibrosarcoma, 10 schwannomas, 1 perineurioma, 2 neurothekeomas, and 14 blue and 26 other nevi for CD-68, HMB-45-defined antigen, S 100 and neurofilament protein. A positive staining for CD 68 was observed in 38 of 42 primary, 5 of 6 DMM, and 11 of 12 metastatic melanomas; 6 of 10 schwannomas; 5 of 10 nevi with junctional component and all 14 blue nevi. All 21 neurofibromas, 1 each neurofibrosarcoma and perineurioma, both neurothekeomas, and all 12 nevi with dermal component were CD 68-negative. HBM 45 was expressed by all 44 primary, none of 6 DMM, and 7 of 12 metastatic melanomas; by none of 10 schwannomas, 6 neurofibromas, 1 neurofibrosarcoma, 1 perineurioma and 2 neurothekeomas. Both junctional nevi, 8 of 10 nevi with junctional components, 1 of 10 dermal components of junctional nevi, and 11 of 13 blue nevi were also HMB 45 positive. Except for 1 perineurioma, S 100 decorated all tumors examined. NF was immunoreactive in 1 of 45 conventional melanomas, 2 of 21 neurofibromas, 2 of 10 schwannomas, and 3 of 10 blue nevi; it was non-reactive in all polypoid, desmoplastic and metastatic melanomas; neurofibrosarcoma, perineurioma, neurothekeoma and other nevi. We conclude that the CD-68-reactivity in primary melanomas, neurofibromas, neurofibrosarcomas, perineuriomas, and nevi was similar to that of HMB 45. The significantly higher CD 68-positivity than of HMB 45 in metastatic and desmoplastic melanomas and schwannomas may be of diagnostic value.

Malignant peripheral nerve sheath tumors (MPNST) are highly malignant sarcomas arising either de novo or in transition from neurofibroma. Although relatively little is known of the molecular genetic alterations that underlie their formation, recent DNA sequencing studies have demonstrated the presence of p53 mutations in some MPNST. This tumor-suppressor gene has been implicated in the progression of a variety of human malignancies, including sarcomas. Employing the anti-p53 monoclonal antibody Do-7, this retrospective immunohistochemical study of p53 gene overexpression in MPNST found reactivity to be present in 68% and to be significant in degree in 57%. In contrast, although some degree of p53 overexpression was present in 48% of neurofibromas, none stained strongly and only 1 of the 27 (4%), a cellular example, showed significant staining. No difference in the frequency or degree of p53 staining was noted between MPNSTs from patients with or without neurofibromatosis 1. The observed overexpression of the gene product, possibly the reflection of a p53 gene mutation, suggests a role for p53 in the progression of neurofibroma to MPNST. Although the prognostic of p53 overexpression in MPNST remains to be confirmed, in the present series immunopositive tumors were associated with a shorter median patient survival (18 months) than were tumors showing no reactivity (82 months) (P = .02).

Pelvic neurofibromatosis is a rare disease and rarely involves the prostate. A 19-year-old male presented with irritative and obstructive voiding symptoms. Magnetic resonance imaging showed a large mass extending from the sacral promontory to the perirectal and perivesical spaces and to the proximal root of the penis. The mass also involved the prostate. The characteristics of the mass were highly suggestive for neurofibroma. Prostate biopsy showed neurofibroma, and the immunohistochemistry stain for S-100 protein was positive.

Merkel cells are an integral component of the cutaneous nervous system. They are commonly associated with dermal nerves under normal physiological conditions. We postulated that Merkel cells may be present in increased numbers within the epidermis overlying benign peripheral nerve sheath tumours such as neurilemomas and neurofibromas. Paraffin-embedded skin biopsy specimens from 21 patients with neurilemomas and 26 with neurofibromas, were analysed for the presence of Merkel cells using a standard immunohistochemical assay (avidin-biotin-peroxidase complex system) with an antibody to cytokeratin 8 (CAM 5.2). Ten cases of leiomyomas were examined as controls. Merkel cells were identified in the interfollicular area of the basal cell layer overlying 14 of 21 (67%) neurilemomas and nine of 26 (35%) neurofibromas. Merkel cells were more frequently observed in increased numbers in a linear array within the basal cell layer in neurilemomas than in neurofibromas, where they were found as individual cells. No Merkel cells were found in the epidermis overlying leiomyomas. The results of this study suggest that Merkel cells are quantitatively increased in the basal cell layer of the epidermis overlying benign peripheral nerve sheath tumours, particularly neurilemomas.

Immunohistochemical analysis of five paraffin wax-embedded neoplasms was performed to elucidate the characteristics of bovine nervous-tissue tumours. In case 1 (peripheral neuroblastoma), the neoplastic tissue was characterized by the formation of true and Homer-Wright rosettes and the existence of neuron-specific enolase. The neoplastic cells were possibly more immature than those of common neuroblastomas, because similar features are observed in human malignant neuroepitheliomas. The neoplastic cells in case 2 (ganglioneuroblastoma) ranged from large cells with abundant neurofilaments to immature small cells, rarely with neurofilaments or glial fibrillary acidic protein (GFAP). Such expression suggests the presence of pluripotential cells. The neoplastic tissue in case 3 (anaplastic ganglioglioma) was strikingly polymorphous, and had five elements; neuronal, astrocytic, oligodendrocytic, spindle cell and small oval cell. The neoplastic neurocytes and astrocytes were, respectively, characterized by neurofilament and GFAP positivity. The neoplastic oligodendrocytes made a honeycomb appearance, and the neoplastic spindle cells and small oval cells were considered to be less differentiated. The tumours of cases 2 and 3, which contained poorly differentiated cells and revealed both neuronal and glial differentiation, may be specific to calves. In case 4 (schwannoma), almost all the neoplastic cells were positive for S100 protein, while S100-negative fibroblasts were present in many areas of case 5 (neurofibroma). These two tumours were readily distinguished histologically and immunohistochemically.

Neurofibroma type 1 tissue was investigated for the presence of growth-promoting activity on human neuroblastoma cells. The activity was isolated by gel filtration and reversed-phase column chromatographs from neurofibroma type 1 extracts. An adenosine-containing dinucleotide (adenylyl(3'-5')cytidine-3'-phosphate) was identified as one of the major components of the activities by its enzymatic fragmentation and liquid chromatography/mass spectrometry. Synthetic adenosine-containing dinucleotide derivatives such as cytidyl(3'-5')adenosine, cytidyl(2'-5')adenosine, adenylyl(3'-5')cytidine, and adenylyl(2'-5')cytidine showed a similar action. Cytidyl(3'-5')adenosine, cytidyl(2'-5')adenosine, and adenylyl(2'-5')cytidine, which are able to release a free adenosine through enzymatic hydrolysis, in particular elicited a strong activity corresponding to that of adenosine with the highest action. These results suggest that neuroblastoma cells are able to use adenosine-containing dinucleotides as well as mononucleotides for their survival and proliferation.

An unusual form of subcutaneous soft tissue tumour with benign character is reported. The tumour was composed of uniform cells which were epithelioid in appearance. True myxoid matrix, osteoid formation or metaplastic bone were not present. Immunohistochemically S-100 protein and vimentin was demonstrated in the tumour cells. Electron microscopic examinations showed fragmented or continuous basal lamina, interdigitating cytoplasmic projections, myelin-like figures and a few cell junctions. The immunohistochemical and electron microscopic results indicate that the tumour is of Schwann's cell origin. Based on light microscopic, electron microscopic and immunohistochemical results we think our case is an epithelioid benign schwannoma but the non-ossifying form of fibromyxoid tumour of the soft parts cannot be excluded with confidence.

Mucosal neuromas (MN), a component of multiple endocrine neoplasia (MEN) type IIb, may be confused histologically with plexiform neurofibromas (PN), a component of neurofibromatosis. The ability to distinguish between these two markers for different genetic diseases is crucial, as the risk of development of medullary thyroid carcinoma and pheochromocytoma in affected patients with MEN IIb is great. We studied two cases each of MN and PN by immunocytochemistry (IC). Epithelial membrane antigen (EMA) proved to be the most useful marker. MN consisted of bundles of disorganized and tortuous nerve fibers surrounded by a thickened perineurium that expressed the cellular phenotype EMA(+), S-100(-). PN consisted of enlarged nerve fascicles with a loose myxoid stroma and was EMA negative. Thus, IC highlighted the differing pattern of growth and histogenesis of the proliferating cells in the two lesions and is likely to be especially useful in those lesions with atypical histology.

Neurofibroma tissue was investigated for the presence of glial growth modulators that would suppress the proliferation of glial cells. A novel endogenous polypeptide inhibitor of proliferation and DNA synthesis in glial cells, gliostatin, was purified from the extracts of neurofibroma by a procedure comprising dye and anion-exchange column chromatography, and HPLC. A monoclonal antibody raised against partially purified gliostatin showed no cross-reactivity with known cytokines, but adsorbed the growth inhibitory activity of gliostatin and immunochemically visualized the putative gliostatin bands on western blot analyses. Although the product showed an apparent M(r) of 100,000 accompanied by an inhibitory activity on gel filtration column chromatography, it migrated at a lower apparent M(r) of 50,000 under the reducing conditions on western blotting, indicating that a homodimeric structure of native gliostatin consisted of 50-kDa subcomponents. Gliostatin was a potent growth inhibitor acting at nanomolar concentrations against all glial tumor cells and glia maturation factor-stimulated astroblasts, but not neuronal cells.