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PubMed1990

Neurofibromas and neurotized melanocytic nevi are immunohistochemically distinct neoplasms.

Neurofibromas are often clinically, as well as histologically, indistinguishable from completely neurotized melanocytic nevi. We tested the hypothesis that immunologic markers would differentiate the perineural fibroblasts and Schwann cells of neurofibromas from the neurotized cells of melanocytic origin. We examined eight partially neurotized acquired melanocytic nevi, three partially neurotized congenital melanocytic nevi, and five neurofibromas, with antibodies directed against S-100 protein, Leu-7(HNK-1), glial fibrillary acid protein (GFAP), and myelin-basic protein (MBP). A histologic diagnosis of neurofibroma was based on identification of a dermal proliferation of spindle-shaped cells with wavy nuclei, in a background of loose reticulated collagen. Neurotized nevi were diagnosed upon recognition of scattered nests of type A or B nevus cells, surrounded by basement membrane, present in the papillary dermis of lesions otherwise indistinguishable from neurofibromas. The congenital nevi were all large melanocytic nevi known to be present at birth. S-100 stained the majority of neoplastic cells in all neurofibromas, neurotized acquired nevi, and neurotized congenital nevi. Neurofibromas showed focal staining for Leu-7, GFAP, and MBP. In contrast, neurotized acquired and congenital nevi failed to express these markers. We believe that Leu-7, GFAP, and MBP may be helpful in differentiating neurofibromas from completely neurotized melanocytic nevi. The differences in the immunohistochemical profiles of neurofibromas and neurotized nevi support the concept that these neoplasms are histogenically distinct, despite their similar histologic appearance.

Antigens, Differentiation↗

PubMed2000

Long-term culture and characterization of human neurofibroma-derived Schwann cells.

Neurofibromas are benign tumors arising from the peripheral nerve sheath and are a typical finding in neurofibromatosis type 1 (NF1). Schwann cells are the predominant cell type in neurofibromas and thus are supposed to play a major role in the pathogenesis of these tumors. It is not known, however, if NF1 mutations in Schwann cells result in an altered phenotype that subsequently leads to tumor formation. To characterize the biological properties of neurofibroma-derived Schwann cells we developed cell culture techniques that enabled us to isolate Schwann cells from neurofibromas and grow them in vitro for several weeks without significant fibroblast contamination. Neurofibroma-derived Schwann cells were characterized by altered morphology, heterogeneous growth behavior, and increased expression of the P0 antigen while several other features of normal human Schwann cells were retained. We conclude that neurofibroma-derived Schwann cells exhibit a distinct phenotype in vitro but that the observed abnormalities by themselves are insufficient to explain neurofibroma formation. Application of our improved culture conditions makes neurofibroma-derived Schwann cells readily available for further studies to define their role in tumorigenesis in neurofibromatosis type 1.

Adolescent↗

PubMed1985

Tissue culture studies of neurofibromatosis: effects of axolemmal fragments and cyclic adenosine 3',5'-monophosphate analogues on proliferation of Schwann-like and fibroblast-like neurofibroma cells.

Six dermal neurofibromas obtained from 5 patients with neurofibromatosis were dissociated and the cells were plated on polylysine-coated glass. Two principal cell types were observed in the cultures: elongated and bipolar Schwann-like cells (SLCs), and polymorphic flattened fibroblast-like cells (FLCs). Indirect immunofluorescence demonstrated that SLCs expressed surface laminin but not surface fibronectin; FLCs expressed surface fibronectin but were only weakly positive for surface laminin. Tritiated thymidine autoradiography demonstrated that cultured SLCs proliferated slowly (labeling index, 0.7 to 4.0%), whereas FLCs divided more rapidly (labeling index, 7.5 to 26.4%). Axolemmal fragments prepared from human or rat central nervous system specimens adhered to SLCs derived from each of the 6 neurofibromas, but not to FLCs. Axolemmal fragments induced a marked proliferative response of SLCs from 2 of the 6 neurofibromas but had no effect on proliferation of SLCs from the other 4 neurofibromas or FLCs from any of the 6 neurofibromas. In one patient from whom 2 neurofibromas were obtained, SLCs from one neurofibroma responded to axolemmal fragments, while SLCs from the other did not. Treatment of the cultures with 0.1 mM cyclic adenosine 3'5'-monophosphate (cAMP) analogue, 8-bromo cAMP, caused marked inhibition of proliferation of both SLCs and FLCs derived from all 6 neurofibromas. The same concentration of another cAMP analogue, dibutyryl cAMP, inhibited proliferation of SLCs but not of FLCs.

Adult↗

PubMed1998

Analysis of vascularity of human neurofibromas.

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.

Endothelial Growth Factors↗

PubMed2002

Plexiform neurofibromas in NF1: toward biologic-based therapy.

Neurofibromatosis type 1 (NF1) is one of the most common neurogenetic diseases affecting adults and children. Neurofibromas are one of the most common of the protean manifestations of NF1. Plexiform neurofibromas, which will frequently cause cosmetic abnormalities, pain, and neurologic deficits, are composed of "neoplastic" Schwann cells accompanied by other participating cellular and noncellular components. There is increasing evidence that loss of NF1 expression in neoplastic Schwann cells is associated with elevated levels of activated RAS, supporting the notion that the NF1 gene product, neurofibromin, acts as a growth regulator by inhibiting ras growth-promoting activity. In addition, there is increasing evidence that other cooperating events, which may be under cytokine modulation, are important for neurofibroma development and growth. Treatment of plexiform neurofibromas has been empiric, with surgery being the primary option for those with progressive lesions causing a major degree of morbidity. The efficacy of alternative treatment approaches, including the use of antihistamines, maturation agents, and antiangiogenic drugs, has been questionable. More recently, biologic-based therapeutic approaches, using drugs that target the molecular genetic underpinnings of plexiform neurofibromas or cytokines believed important in tumor growth, have been initiated. Evaluation of such trials is hindered by the unpredictable natural history of plexiform neurofibromas and difficulties in determining objective response in tumors that are notoriously large and irregular in shape. Innovative neuroimaging techniques and the incorporation of quality-of-life scales may be helpful in evaluation of therapeutic interventions. The ability to design more rational therapies for NF1-associated neurofibromas is heavily predicated on an improved understanding of the molecular and cellular biology of the cells involved in neurofibroma formation and growth.

Biological Therapy↗

PubMed2004

Extraaxial neurofibromas versus neurilemmomas: discrimination with MRI.

OBJECTIVE: The purpose of our study was to evaluate whether MRI can discriminate between extraaxial neurofibromas and neurilemmomas. MATERIALS AND METHODS: MR images of 52 patients with a pathologically proven extraaxial neurofibroma or neurilemmoma were retrospectively reviewed by observers who were unaware of the surgical results, regarding the presence or absence of individual imaging criteria. MRI findings in 12 patients with a localized neurofibroma and 40 patients with a neurilemmoma were compared using the chi-square test or Fisher's exact test. RESULTS: MRI findings suggestive of neurofibroma (p < 0.05) were a target sign on T2-weighted images (58% in neurofibromas vs 15% in neurilemmomas), central enhancement (75% vs 8%), and a combination of both findings (63% vs 3%). MRI findings suggestive of a neurilemmoma (p < 0.05) were a fascicular appearance on T2-weighted images (25% vs 63%), a thin hyperintense rim on T2-weighted images (8% vs 58%), a combination of both findings (8% vs 48%), and diffuse enhancement (13% vs 67%). No significant difference was seen between neurofibromas and neurilemmomas for a centrally entering and exiting nerve (42% in neurofibromas vs 23% in neurilemmomas), a peripherally entering and exiting nerve (58% vs 77%), a cystic area (38% vs 64%), a low-signal margin (100% vs 100%), peripheral enhancement (13% vs 26%), or a target sign on contrast-enhanced images (11% vs 31%). CONCLUSION: MRI shows features helpful for differentiating extraaxial neurofibromas from neurilemmomas; however, no single finding or combination of findings allows definitive differentiation.

Adolescent↗

PubMed2003

Progesterone receptor expression in neurofibromas.

Neurofibromas are benign tumors of the peripheral nerve sheath, which occur sporadically and in association with the common familial cancer syndrome, neurofibromatosis type 1. There are intriguing links between the growth of neurofibromas and levels of circulating hormones: neurofibromas often first appear around the time of puberty, increase in number and size during pregnancy, and shrink after giving birth. We examined 59 human neurofibromas for the expression of estrogen and progesterone receptors (PRs), because their ligands, estrogen and progesterone, were attractive candidate hormones. The majority (75%) of neurofibromas expressed PR, whereas only a minority (5%) of neurofibromas expressed estrogen receptor. Within neurofibromas, PR was expressed by non-neoplastic tumor-associated cells and not by neoplastic Schwann cells. We hypothesize that progesterone may play an important role in neurofibroma growth and suggest that antiprogestins may be useful in the treatment of this tumor.

Humans↗

PubMedDate not supplied

Ki-67 proliferation-index (MIB-1) of neurofibromas in neurofibromatosis type 1 patients.

OBJECTIVE: The aim of this study was to analyse the proliferation rate of neurofibromas, in neurofibromatosis type 1 (NF1) patients in order to find out whether tumor growth can be correlated with the different subtypes, size and localisation of tumors, or gender. Large tumors and those localisations that do not allow a complete resection, e.g. the trigeminal branch plexiform neurofibromas, often require repeated surgical interventions. Therefore, the question whether partial resection is associated with alterations of the tumor type and proliferation is of great interest. MATERIALS AND METHODS: We investigated 317 specimens of 96 patients. Twenty-five specimens were identified as local recurrences, all of them being consecutive resections in the previously operated area. All patients were NF 1-affected individuals who fulfilled the US National Institute of Health consensus criteria for defining the disease. The proliferation index (PI) was assessed on formalin-fixed, paraffin-embedded tissue stained with the MIB- 1 antibody (Ki-67 antigen). The PI was evaluated in three high-power fields (0.1 square millimeter) in the area with the highest proliferative activity. The correlations were calculated according to Spearman-Rho. RESULTS: Men were more often surgically treated in the head and neck than women (p < 0.02). Plexiform neurofibromas were more frequently operated on in the head and neck than in other regions (p < 0.01). Older patients were more often treated for the diffuse cutaneous type of neurofibromas (p < 0.0001). The type of tumor did not differ from primaries to recurrent tumors. The MIB- 1 PI showed no association with any of the clinical parameters. In particular, there was no difference of the MIB-1 index between primaries and recurrent tumors. DISCUSSION: This study showed, for the first time, that proliferation in neurofibromas is not enhanced in previously partially resected neurofibromas. Hence, the argument that trauma or surgery for neurofibromas might promote proliferation, especially in the plexiform neurofibroma, is not supported by the results of the present study. Further this analysis demonstrated interdependencies between tumor type, localisation, age and gender indicative of the social difficulties encountered by the NF1 patients which may be helpful for the advising practitioner.

Adolescent↗

PubMed1991

The neurofibroma in von Recklinghausen neurofibromatosis has a unicellular origin.

von Recklinghausen neurofibromatosis (NF1) is the most common hereditary syndrome predisposing to neoplasia. NF1 is an autosomal dominant disease caused by a single gene which maps to chromosome 17q11.2. The most common symptomatic manifestation of NF1 is the benign neurofibroma. Our previous studies of tumors in NF1, studies which detected a loss of heterozygosity for DNA markers from the NF1 region of chromosome 17 in malignant tumors, did not detect a loss in neurofibromas. We report here that a more extensive study, including the analysis of neurofibromas from 19 unrelated NF1 patients by using seven probes, failed to detect a single instance of loss of heterozygosity. This finding suggests that neurofibromas are either polyclonal or monoclonal in origin but arise by a mechanism different from that of NF1 malignancies. In order to investigate the first possibility, we analyzed neurofibromas from female NF1 patients by using an X chromosome-specific probe, from the phosphoglycerokinase (PGK) gene, which detects an RFLP. The detected alleles carry additional recognition sites for the methylation-sensitive enzyme HpaII, so that the allele derived from the active X chromosome is digested by HpaII while the one from the hypermethylated, inactive X chromosome is not. We analyzed neurofibromas from 30 unrelated females with NF1. Eight patients were heterozygous for the PGK RFLP. By this assay, neurofibromas from all eight appeared monoclonal in origin. These results suggest that benign neurofibromas in NF1 arise by a mechanism that is different from that of malignant tumors.(ABSTRACT TRUNCATED AT 250 WORDS)

Blotting, Southern↗

PubMed1997

Confirmation of a double-hit model for the NF1 gene in benign neurofibromas.

Neurofibroma is a benign tumor that arises from small or large nerves. This neoplastic lesion is a common feature of neurofibromatosis type 1 (NF1), one of the most common autosomal dominant disorders. The NF1 gene codes for a protein called "neurofibromin." It possesses a region that shares a high homology with the family of GTPase-activating proteins, which are negative regulators of RAS function and thereby control cell growth and differentiation. The evidence points to the NF1 gene being a tumor-suppressor gene. NF1 patients also have an increased incidence of certain malignant tumors that are believed to follow the "two hit" hypothesis, with one allele constitutionally inactivated and the other somatically mutated. Recently, somatic loss of heterozygosity (LOH) has been described for neurofibromas, and mutations in both copies of the NF1 gene have been reported for a dermal neurofibroma. The aim of our study was the analysis of the NF1 locus in benign neurofibromas in NF1 patients. We performed LOH analysis on 60 neurofibromas belonging to 17 patients, 9 of them with family history of the disease and 8 of them sporadic. We have analyzed five intragenic NF1 markers and six extragenic markers, and we have found LOH in 25% of the neurofibromas (corresponding to 53% of the patients). In addition, we found that in the neurofibromas of patients from familial cases the deletions occurred in the allele that is not transmitted with the disease, indicating that both copies of the NF1 gene were inactivated in these tumors. Therefore, the recent reports mentioned above, together with our findings, strongly support the double inactivation of the NF1 gene in benign neurofibromas.

Alleles↗

PubMed2003

Differentially expressed genes in neurofibromatosis 1-associated neurofibromas and malignant peripheral nerve sheath tumors.

Neurofibromas represent one of the hallmarks of neurofibromatosis 1 (NF1) patients. Tumor progression of neurofibromas to malignant peripheral nerve sheath tumors (MPNST) is a frequent and life threatening complication. To learn more about processes involved in malignant transformation, we evaluated differential gene expression in plexiform neurofibroma and MPNST from the same NF1 patient. Suppression subtractive hybridization (SSH) yielded 133 differentially expressed genes confirmed by reverse Northern blotting. Virtual Northern blots were employed to validate 23 genes. To independently verify differential expression, immunohistochemical analyses with antibodies to matrix metalloproteinase 13 (MMP13), platelet-derived growth factor receptor alpha (PDGFRA) and fibronectin (FN1) were performed on 9 dermal and 9 plexiform neurofibromas and 16 MPNST from 19 NF1 patients. All three proteins proved to be up-regulated in MPNST. MMP13 expression was observed in 44% of MPNST but was absent in neurofibromas. PDGFRA was expressed in all tumors, but the number of cells expressing it was below 30% in neurofibromas and over 50% in MPNST. Likewise, FN1 was expressed in all tumors, but less than 30% of the cells in neurofibromas and more than 70% of the cells in MPNST exhibited antibody binding. Our data point to several genes not previously recognized to be differentially expressed, and provide a framework for future studies on progression-associated gene expression in low- and high-grade nerve sheath tumors.

Adult↗

PubMed2001

Tumorigenic properties of neurofibromin-deficient neurofibroma Schwann cells.

Dermal and plexiform neurofibromas are peripheral nerve sheath tumors that arise frequently in neurofibromatosis type 1. The goal of the present study was to examine the tumorigenic properties of neurofibromin-deficient human Schwann cells (SCs) that were found to represent a subset of SCs present in approximately half of the total neurofibromas examined. Highly enriched SC cultures were established from 10 dermal and eight plexiform neurofibromas by selective subculture using glial growth factor-2 and laminin. These cultures had low tumorigenic potential in classical in vitro assays yet several unique preneoplastic properties were frequently observed, including delayed senescence, a lack of density-limited growth, and a strong propensity to spontaneously form proliferative cell aggregates rich in extracellular matrix. Western blot analysis failed to detect full-length neurofibromin in any of the neurofibroma SC cultures, indicating that neurofibromin-deficient SCs had a substantial growth advantage. Immunohistochemical staining of the originating tumors showed the majority were comprised principally of neurofibromin-negative SCs, whereas the remainder contained both neurofibromin-negative and neurofibromin-positive SCs. Lastly, engraftment of neurofibromin-deficient SC cultures into the peripheral nerves of scid mice consistently produced persistent neurofibroma-like tumors with diffuse and often extensive intraneural growth. These findings indicate that neurofibromin-deficient SCs are involved in neurofibroma formation and, by selective subculture, provide a resource for the development of an in vivo model to further examine the role of these mutant SCs in neurofibroma histogenesis.

Adolescent↗

PubMedDate not supplied

[Melanotic neurofibroma].

BACKGROUND: Melanotic neurofibromas are rare tumours. The clinical and histological diagnosis is often difficult to make. CASE REPORT: A 41 year-old woman with type-1 neurofibromatosis presented with an old, large (16 cm by 6 cm) pigmented tumour on her left arm. It was initially considered to be a congenital naevus. Partial surgical resection was performed. Histological examination showed a loose proliferation of spindle-cells within the dermis and subcutaneous layers, with multiple foci of melanin-laden cells but no mitotic figures or atypical cells. There was no melanocytic theca. The tumour had immunoreactivity for the S-100 protein, neuron-specific-enolase, neurofilaments, synaptophysin, A-103 and HMB-45. The association of a benign pigmented tumour producing melanin and the presence of Schwann cells and nervous cells, led to the diagnosis of diffuse melanotic neurofibroma. DISCUSSION: Melanotic neurofibromas can occur on their own or be associated with neurofibromatosis. They must be distinguished from classical neurofibromas when pigmentation occurs in the latter. Melanotic neurofibromas usually appear in the second or third decade of life and rarely in childhood. It is worth noting that hairs may overlie a melanotic neurofibroma, mimicking a giant naevus or a neurocristic cutaneous hamartoma. These are the two main differential diagnoses among children. Among adults, the main difficulty is to distinguish melanotic neurofibroma from pigmented dermatofibrosarcoma, because of the clinical and histological similarities between these two.

Adult↗

PubMed1990

Angiogenic and invasive properties of neurofibroma Schwann cells.

Neurofibromas are benign tumors from patients with von Recklinghausen Neurofibromatosis (NF1) that are comprised primarily of Schwann cells. These Schwann cells are found both in association with axons and in the extracellular matrix that is prevalent in neurofibromas, and in which fibroblasts are also abundant. An unresolved question has been whether cells in neurofibromas are normal cells or are intrinsically abnormal. We have tested the hypothesis that cells in neurofibromas are abnormal and have shown that neurofibroma Schwann cells, unlike normal Schwann cells, promote angiogenesis in the chick chorioallantoic membrane model system, and invade basement membranes in this system. In contrast, neurofibroma fibroblasts neither promote angiogenic reactions nor invade basement membranes. When injected into nude mice, neurofibroma Schwann cells do not form progressive tumors. These results suggest that NF1 Schwann cells differ from normal Schwann cells, that they are preneoplastic, and that genetic and/or epigenetic changes in Schwann cells may be required for development of peripheral nerve tumors in NF1.

Allantois↗

PubMed2000

Schwann cells harbor the somatic NF1 mutation in neurofibromas: evidence of two different Schwann cell subpopulations.

Neurofibromas are one of the most characteristic features of neurofibromatosis type 1 (NF1), an inherited autosomal-dominant neurogenetic disorder affecting 1 in 3500 individuals worldwide. These benign tumors mainly consist of Schwann cells (SCs) and fibroblasts. Recent evidence demonstrates that somatic mutations at the NF1 gene are found in neurofibromas, but it has not been demonstrated whether SCs, fibroblasts and/or both cell types bear a somatic loss of NF1. We recently established a cell culture system that allows selective expansion of human SCs from neurofibromas. We cultured pure populations of SCs and fibroblasts derived from 10 neurofibromas with characterized NF1 mutations and found that SCs but not fibroblasts harbored a somatic mutation at the NF1 locus in all studied tumors. Furthermore, by culturing neurofibroma-derived SCs under different in vitro conditions we were able to obtain two genetically distinct SC subpopulations: NF1(-/-) and NF1(+/-). These data strongly support the idea that NF1 mutations in SCs, but not in fibroblasts, correlate to neurofibroma formation and demonstrate that only a portion of SCs in neurofibromas have mutations in both NF1 alleles.

Cell Division↗

PubMed2000

Evaluation of (18)fluorodeoxyglucose positron emission tomography ((18)FDG PET) in the detection of malignant peripheral nerve sheath tumours arising from within plexiform neurofibromas in neurofibromatosis 1.

OBJECTIVES: The ability of (18)fluorodeoxyglucose positron emission tomography ((18)FDG PET) to detect malignant change in plexiform neurofibromas from patients with neurofibromatosis 1 (NF1) was evaluated. METHODS: Eighteen NF1 patients who presented with pain, increase in size, or neurological deficit associated with a plexiform neurofibroma were assessed. Magnetic resonance imaging determined the site and extent of the lesion. Qualitative(18)FDG PET was performed and the standard uptake value (SUV) measured the regional glucose metabolism. Histological confirmation of the diagnosis was obtained in 10 patients. RESULTS: Twenty three plexiform neurofibromas were detected in 18 patients. Seven malignant peripheral nerve sheath tumours, four high grade and three low grade tumours, occurred in five patients. In one patient the clinical and radiological characteristics of the tumour suggested malignancy, but histology was inconclusive. Fifteen benign plexiform neurofibromas were identified in 12 patients and these findings were confirmed histologically in five lesions from four patients. Ten plexiform neurofibromas occurring in eight patients were considered benign on(18)FDG PET and the patients did not undergo surgery. They remained stable or their symptoms improved on clinical follow up (median 9 months). The results of qualitative (18)FDG PET were interpreted as indicating that 13 plexiform neurofibromas were benign and 10 were malignant. No malignant tumours were classified as benign, but two benign tumours were reported as malignant. The SUV was calculated for 20 tumours and was significantly higher in five malignant tumours 5.4 (SD 2.4), than in 15 benign tumours 1.54 (SD 0.7), p=0.002. There was an overlap between benign and malignant tumours in the SUV range 2.7-3.3. CONCLUSIONS: (18)FDG PET is helpful in determining malignant change in plexiform neurofibromas in NF1. Increased separation between benign and malignant lesions could be obtained by calculating the SUV at about 200 minutes after injection of (18)FDG, when the peak activity concentration is obtained in malignant tumours.

Adolescent↗

PubMed1989

Mast cell and lymphoreticular infiltrates in neurofibromas. Comparison with nerve sheath tumors.

Cellular heterogeneity produced by non-Schwannian elements may distinguish neurofibromas from other Schwann cell neoplasma and contribute to a different tumor biology. The present study compared cell counts of mast cells, T and B lymphocytes, and macrophages in 32 neurofibromas with those in 27 schwannomas, 9 malignant nerve sheath tumors, and 17 traumatic neuromas. Immunohistochemical and histochemical analyses were performed on formalin-fixed, paraffin-embedded tissues using two monoclonal antibodies against B-lymphocyte epitopes (LN-1 and LN-2), one monoclonal antibody against T-lymphocyte epitopes (UCHL-1), one polyclonal antibody recognizing alpha 1-antichymotrypsin (ACT), a macrophage/histiocytemarker, and toluidine blue O stains. Neurofibromas contained relatively high concentrations of mast cells significantly greater than the concentrations in other neoplastic or reactive nerve sheath tumors. Most neurofibromas also displayed moderate concentrations of LN-2 immunoreactive cells, similar to the concentrations in traumatic neuromas and not statistically different from cell counts in other tumor types. Limited, variable LN-1 and UCHL-1 immunoreactive infiltrates were detected in neurofibromas and some peripheral schwannomas. Rare or moderate ACT immunoreactivity was detected in the majority of neurofibromas, in contrast with the absence, or rare appearance, of ACT immunostaining in cranial and peripheral nerve schwannomas and moderate numbers of immunoreactive cells in many malignant nerve sheath tumors. Mast cells are an important cellular marker of neurofibromas and may participate in the pathogenesis of these neoplasms.

Antibodies, Monoclonal↗

PubMed1995

[Exclusive nodular plexiform neurofibroma. An unusual case of neurofibromatosis type 1].

INTRODUCTION: Type 1 neurofibromatous tumours (NF) are benign skin tumours which include cutaneous, subcutaneous and plexiform neurofibromas. Plexiform neurofibromas are either diffuse or nodular, the latter form being much more frequent. CASE REPORT: We observed a particular form of neurofibroma in an 18-year-old patient who developed large deep subcutaneous which histology examination revealed to be exclusively nodular plexiform neurofibromas. The patient also had 6 café au lait spots leading to the diagnosis of sporadic NF 1. He did not have acoustic neuronoma, schwannoma or posterior cataract, eliminating NF 2. COMMENTS: In NF 1, subcutaneous neurofibromas develop in 5 p. 100 of the patients. These lesions are termed nodular plexiform neurofibromas when they form long formations along nerve branches. The exclusive nature of the nodular plexiform neurofibromas in our case was exceptional. It could be hypothesized that the particular phenotype in our patient might correspond to a particular anomaly of the NF 1 gene.

Adolescent↗