Low-grade Malignant Peripheral Nerve Sheath Tumors Research Articles

Consensus recommendations for an integrated diagnostic approach to peripheral nerve sheath tumors arising in the setting of Neurofibromatosis type 1 (NF1).

Consensus recommendation published in 2017 histologically defining atypical neurofibromatous neoplasm of uncertain biologic potential (ANNUBP) and malignant peripheral nerve sheath tumor (MPNST) were codified in the 2021 WHO Classification of Tumors of the Central Nervous System and the 2022 WHO Classification of Tumors of Soft Tissue and Bone. However, given the shift in diagnostic pathology toward the use of integrated histopathologic and genomic approaches, the incorporation of additional molecular strata in the classification of Neurofibromatosis Type 1 (NF1)-associated peripheral nerve sheath tumors should be formalized to aid in accurate diagnosis and early identification of malignant transformation to enable appropriate intervention for affected patients. To this end, we assembled a multi-institutional expert pathology working group as part of a "Symposium on Atypical Neurofibroma: State of the Science". Herein, we provide a suggested framework for adequate interventional radiology and surgical sampling, and recommend molecular profiling for clinically or radiologically worrisome non-cutaneous lesions in patients with NF1 to identify diagnostically-relevant molecular features, including CDKN2A/B inactivation for ANNUBP, as well as SUZ12, EED, or TP53 inactivating mutations, or significant aneuploidy for MPNST. We also propose renaming "low-grade MPNST" to "ANNUBP with increased proliferation" to avoid the use of the "malignant" term in this group of tumors with persistent unknown biologic potential. This refined integrated diagnostic approach for NF1-associated peripheral nerve sheath tumors should continue to evolve in concert with our understanding of these neoplasms.

Multiple Gastrointestinal Stromal Tumors, Malignant Peripheral Nerve Sheath Tumor and Atypical Neurofibromatous Neoplasm With Uncertain Biologic Potential Developing in A Single Patient With Neurofibromatosis Type 1 Syndrome.

Neurofibromatosis type 1 (NF1) is the most common human genetic disease. In these patients, the incidence of malignant peripheral nerve sheath tumors (MPNST) and gastrointestinal stromal tumors (GIST) is increased. A male patient in his forties with neurofibromatosis 1, presented with the coexistence of multiple GISTs located at intestinal and colonic mesentery, MPNST located at his leg and atypical neurofibromatous neoplasm with uncertain biologic potential located at colonic mesentery. By FISH, the MPNST harbored CDKN2A loss and recurred 1 year later. After reresection and radiotherapy, the patient is now disease-free without evidence of disease. Atypical neurofibromatous neoplasm with uncertain biologic potential is a newly defined entity, and it is important to discriminate it from low-grade MPNST, which requires more aggressive treatment methods. To the best of our knowledge, this is the first report describing synchronous GISTs, MPNST, and atypical neurofibromatous neoplasm with uncertain biologic potential developing in a single NF1 patient.

Magnetic Resonance Imaging Features for Differentiating Low-Grade and High-Grade Malignant Peripheral Nerve Sheath Tumors.

This study aimed to assess the usefulness of magnetic resonance imaging (MRI) findings for differentiating low-grade and high-grade malignant peripheral nerve sheath tumors (MPNSTs). This study included 31 patients (onset age range, 19-83 years; mean onset age, 57 years; 9 men and 22 women) with 36 histopathologically proven MPNSTs (7 low-grade MPNSTs and 29 high-grade MPNSTs) who underwent preoperative MRI between December 2007 and October 2022. Quantitative and qualitative MRI findings were retrospectively evaluated and compared between the 2 subtypes. The maximum tumor diameter (106.1 ± 64.0 vs 54.9 ± 19.8 mm, P = 0.032) and tumor-to-muscle signal intensity ratio (SIR) of fat-suppressed gadolinium-enhanced T1-weighted images (2.69 ± 1.40 vs 1.62 ± 0.40, P = 0.005) were significantly higher in high-grade MPNSTs than in low-grade MPNSTs. The receiver operating characteristic analysis revealed that the tumor-to-muscle SIR of fat-suppressed gadolinium-enhanced T1-weighted images exhibited the highest area under the curve value (0.88), followed by the maximum tumor diameter (0.76). The sensitivity and specificity of the tumor-to-muscle SIR of fat-suppressed gadolinium-enhanced T1-weighted images for diagnosing high-grade MPNST at an optimal SIR threshold of greater than 1.73 were 90% and 83%, respectively. However, other MRI findings showed no significant differences between the 2 subtypes ( P = 0.16-1.00). Although the MRI findings of low-grade and high-grade MPNST overlapped considerably, the maximum tumor diameter and degree of contrast enhancement can be used to differentiate low-grade MPNST from high-grade MPNST.

Analysis of H3k27me3 Expression in Malignant Peripheral Nerve Sheath Tumor (MPNST) and Other Spindle Cell Sarcoma Mimicking MPNST

Malignant Peripheral Nerve Sheath Tumor (MPNST) is a type of spindle cell sarcoma with approximately 5% of all sarcomas. Its diagnosis is challenging due to the absence of specific immunohistochemical markers. Recently, H3K27me3 was discovered as a potential specific immunohistochemical marker to differentiate MPNST from other sarcomas and distinguish between low and high-grade MPNST. Therefore, this research aims to investigate the use of the H3K27me3 as a potential specific marker for Malignant Peripheral Nerve Sheath Tumor (MPNST). A cross-sectional analysis was conducted on 50 cases of sarcomas, including 13 MPNST, 14 synovial sarcomas, 13 dermatofibrosarcoma protuberans (DFSP), and 10 leiomyosarcomas originating from the Department of Anatomical Pathology, Faculty of Medicine, Universitas Indonesia, Cipto Mangunkusumo Hospital (FMUI-CMH) from January 2013 to December 2021. H3K27me3 images were obtained and categorized as complete loss when more than 95% of the tumor cells showed loss of nuclear staining. The results found in MPNST showed a loss of H3K27me3 expression, which is statistically significant compared to other sarcomas mimicking MPNST (p=0.021), indicating its potential as a diagnostic marker. There is a difference in the expression of H3K27me3 between the high and low-grade MPNST but it is not statistically significant (p=0.105). This showed that H3K27me3 loss of expression can be used to diagnose MPNST, especially high-grade MPNST, and differentiate it from other sarcomas mimicking MPNST.

A resected case of malignant peripheral nerve sheath tumor arising in the cervical esophagus

We report herein a case of malignant peripheral nerve sheath tumor (MPNST), an extremely rare, esophageal malignancy. A 67-year-old, female patient presented with a nodular lesion in the cervical esophagus which was detected on follow-up computed tomography (CT) after surgery for bilateral breast cancer and gastric cancer. Upper gastrointestinal endoscopy revealed a hemispheric, submucosal lesion in the cervicothoracic esophagus. Endoscopic ultrasound-guided fine needle aspiration cytology revealed spindle-shaped cells with nuclear atypia and positive staining for the S100 protein, a neurogenic marker. Based on clear CT findings of lesion growth over two years, MPNST was diagnosed, and treatment for sarcoma was begun. After one course of preoperative chemotherapy, open resection of the esophagus was performed, revealing a solid, white tumor with a maximum diameter of 1.8 cm. The tumor was histopathologically found to be located within the intrinsic muscularis propria. Based on this finding, low-grade MPNST with a schwannoma-like component at its margins was diagnosed. Approximately 50% of MPNST cases occur against a background of neurofibromatosis type 1 (NF1) while about 40% occur sporadically, and 10% occur after irradiation. The patient’s history of radiotherapy for left breast cancer may have contributed to the development of the MPNST.

Differences in MMP-2 Expression in High- and Low-Grade MPNST and its Correlation with Prognostic Factors

Malignant peripheral nerve sheath tumor (MPNST) is a soft tissue sarcoma, which is difficult to distinguish from other spindle cell sarcomas. MPNST is hostile, with a high recurrence, and tends to metastasize hematogenously, especially to the lungs. A phase of the metastasis is a degradation of the extracellular matrix, where Matrix Metalloproteinase (MMP) plays an essential role in this process. Gelatinase-type MMP, MMP-2 and MMP-9, can degrade basal membrane and fibrillar collagen to open the invasion pathway. MMP-2 can degrade more collagen and non-collagen extracellular matrix than MMP-9. Therefore, the study aimed to see the relationship between MMP-2 overexpression and histopathological malignancy grading and other clinical prognostic variables. The study was conducted by immunohistochemical staining of MMP-2 in 39 cases, consisting of 19 cases of low-grade MPNST and 20 cases of high-grade MPNST. Subsequently, an analysis of the relationship between MMP-2 overexpression and the malignancy grading and clinical variables was performed, such as age, sex, and tumor size and location. MMP-2 overexpression was seen in 19 (95%) cases of high grade and three (15.8%) cases of low-grade MPNST (p 0.000). The study also found a significant relationship between MMP-2 overexpression and histopathology grading, which may be helpful to define the prognosis.

Limitations and benefits of FDG-PET/CT in NF1 patients with nerve sheath tumors: A cross-sectional/longitudinal study.

The purposes of this study were to re‐confirm the usefulness of PET/CT in the differentiation of benignity/malignancy of neurogenic tumors in NF1 patients, and to analyze the natural course of plexiform neurofibroma (pNF) and clarify whether PET/CT is also useful for detecting tumors other than neurogenic tumors. PET/CT was prospectively imaged in 36 NF1 patients. There were 14 malignant peripheral nerve sheath tumors (MPNSTs) in 14 patients, and 54 pNFs in 30 patients. Nine patients had both MPNST and pNF. Maximal standardized uptake value (SUVmax) was significantly higher in MPNST (median 7.6: range 4.1‐10.4) (P < .001) compared with that of pNF (median 3.7: range 1.6‐9.3). The cut‐off value of 5.8 resulted in a sensitivity of 78.6% and specificity of 88.9%. Median age was 29 y, and median maximum tumor diameter was 82 mm in 14 MPNST patients. The 5‐y overall survival rate was 46.8%. Three patients with low‐grade MPNST were alive without disease at the time of this report. In 9 patients in which pNF and MPNST co‐existed, 2 showed a higher SUVmax of pNF than that of MPNST. Natural history analysis of pNF (n = 43) revealed that no factors significantly correlated with increased tumor size. Nine lesions other than neurogenic tumors were detected by PET/CT including 5 thyroid lesions and 3 malignant neoplasms. This study revealed the usefulness and limitation of PET/CT for NF1 patients. In the future, it will be necessary to study how to detect over time the malignant transformation of pNF to MPNST, via an intermediate tumor.

Review and update in the diagnosis of peripheral nerve sheath tumors.

Although tumors with nerve sheath differentiation are vast, the main clinically significant problems faced by the pathologist are the separation of malignant peripheral nerve sheath tumors (MPNSTs) from histologic mimics, the diagnosis of neurofibromatous neoplasms with atypical features, and the separation of cutaneous neurofibromatous neoplasms from melanoma. This review briefly discusses a variety of common nerve sheath tumors and summarizes recent advances on these diagnostic fronts. Much of recent work has focused on abnormalities in polycomb repressive complex 2, and the ways in which these abnormalities may be exploited in the diagnosis of MPNSTs. Progress has been made in the diagnostic and clinical understanding of atypical neurofibromatous neoplasms and low-grade MPNSTs. A number of reports have explored the diagnostic distinction between cutaneous neurofibroma and melanoma. New discoveries show promise in the diagnosis of peripheral nerve sheath tumors, but challenges - old and new - remain.

The Value of H3K27me3 Immunohistochemistry in Differentiating Malignant Peripheral Nerve Sheath Tumour with Its Histologic Mimickers.

Background:Diagnosis of malignant peripheral nerve sheath tumor (MPNST) is rather challenging due to its divergent morphologic heterogeneity and lack of specific ancillary test. The emergence of H3K27 trimethylation (H3K27me3) as a new immunohistochemistry (IHC) marker for MPNST have recently available to assist pathologists in differentiating MPNST from other histologic mimics. We aim to study the expression pattern of H3K27me3 in MPNST and its histologic mimickers and their association with the clinicopathological data. Methodology:A total of 59 benign and malignant spindle cell tumours (18 MPNST and 41 of its histologic mimickers which included 10 schwannoma, 13 neurofibroma, 4 synovial sarcoma, 3 fibrosarcoma, 2 gastrointestinal stromal tumour (GIST), 4 leiomyosarcoma, 1 spindle cell liposarcoma, 1 solitary fibrous tumour, 2 low grade fibromyxoid sarcoma and 1 unclassified spindle cell sarcoma), diagnosed from January 1998 to April 2018 in Hospital Universiti Sains Malaysia (HUSM) were tested for H3K27me3 by IHC. The MPNST histological grade was assessed based on the French Fe’de’ ration Nationale des Centres de LutteContre le Cancer (FNCLCC) for 3 tiers system (low grade, intermediate grade and high grade). The clinicopathological data were retrieved from the patients’ record. Results:A total of 61.1% (11/18 MPNST) showed loss of H3K27me3 expression which is statistically significant as compared to its histologic mimics (p<0.001). Similar findings (p=0.026) were also observed in high grade MPNST (81.8%), intermediate grade MPNST (100%) and 0% in low grade MPNST. Conclusion: H3K27me3, combined with other panel of markers, is useful in MPNST diagnosis to differentiate it from the histological mimickers.

Safe marginal resection of atypical neurofibromas in neurofibromatosis type 1.

Patients with neurofibromatosis type 1 (NF1) are predisposed to visceral neurofibromas, some of which can progress to premalignant atypical neurofibromas (ANFs) and malignant peripheral nerve sheath tumors (MPNSTs). Though subtotal resection of ANF may prevent malignant transformation and thus deaths with no neural complications, local recurrences require reoperation. The aim of this study was to assess the surgical morbidity associated with marginal resection of targeted ANF nodules identified via preoperative serial volumetric MRI and 18F-FDG-PET imaging. The authors analyzed clinical outcomes of 16 NF resections of 21 tumors in 11 NF1 patients treated at the NIH Clinical Center between 2008 and 2018. Preoperative volumetric growth rates and 18F-FDG-PET SUVMax (maximum standardized uptake value within the tumor) of the target lesions and any electromyographic or nerve conduction velocity abnormalities of the parent nerves were measured and assessed in tandem with postoperative complications, histopathological classification of the resected tumors, and surgical margins through Dunnett's multiple comparisons test and t-test. The surgical approach for safe marginal resection of ANF was also described. Eleven consecutive NF1 patients (4 male, 7 female; median age 18.5 years) underwent 16 surgical procedures for marginal resections of 21 tumors. Preoperatively, 13 of the 14 (93%) sets of serial MRI studies and 10 of the 11 (91%) 18F-FDG-PET scans showed rapid growth (≥ 20% increase in volume per year) and avidity (SUVMax ≥ 3.5) of the identified tumor, respectively (median tumor size 48.7 cm3; median growth rate 92% per year; median SUVMax 6.45). Most surgeries (n = 14, 88%) resulted in no persistent postoperative parent nerve-related complications, and to date, none of the resected tumors have recurred. The median length of postoperative follow-up has been 2.45 years (range 0.00-10.39 years). Histopathological analysis confirmed significantly greater SUVMax among the ANFs (6.51 ± 0.83, p = 0.0042) and low-grade MPNSTs (13.8, p = 0.0001) than in benign neurofibromas (1.9). This report evaluates the utility of serial imaging (MRI and 18F-FDG-PET SUVMax) to successfully detect ANF and demonstrates that safe, fascicle-sparing gross-total, extracapsular resection of ANF is possible with the use of intraoperative nerve stimulation and microdissection of nerve fascicles.

Fascicle Sparing Capsular Resections of Atypical Neurofibromas in Neurofibromatosis 1

Abstract INTRODUCTION Neurofibromatosis type 1 (NF1) patients are predisposed to neurofibromas (NF), which can progress to premalignant atypical neurofibromas (ANF) and malignant peripheral nerve sheath tumors (MPNST). Subtotal resection of ANF may prevent metastases and deaths, but local recurrences require reoperation. Here, we assess the surgical morbidity associated with gross total, extracapsular resection of targeted ANF nodules identified via serial volumetric magnetic resonance imaging (MRI) and 18F-FDG-PET imaging. METHODS We retrospectively analyzed the clinical outcomes of 11 NF1 patients following 16 NF surgical resections of 21 tumors at the NIH Clinical Center between 2008 and 2018. Preoperative volumetric growth rates and 18F-FDG-PET SUVMAX of the target lesions were measured and assessed in tandem with postoperative complications, histopathological classification of the resected tumors, and surgical margins through Dunnett's multiple comparison tests and t-tests. RESULTS Preoperatively, 13 of the 14 (93%) sets of serial preoperative MRI scans showed rapid growth ( = 20% increase in volume per year), and 10 of the 11 (91%) 18F-FDG-PET scans indicated increased positron emission tomography (PET) avidity (median SUVMax = 6.45). Gross total, extracapsular resections of the targeted neurofibroma nodules were annotated by the surgeon in all 16 (100%) surgeries, and most surgeries (n = 14, 88%) resulted in no persistent postoperative parent nerve-related complications. SUVMax was significantly greater in the ANF (6.51 ± 0.83, P = .0042) and low grade MPNST (13.8, P = .0001) strata than in the benign NF (1.9) stratum. To date, none of the resected NF have recurred. CONCLUSION This study confirms that the combination of increased 18F-FDG-PET SUVMax, rapid growth, and pain can serve as reliable indicators of atypical transformation and the need for surgical intervention. We also demonstrate the ability to achieve safe, fascicle-sparing gross total, extracapsular resection of ANF using intraoperative nerve stimulation, histological verification, and continued monitoring for tumor recurrence.

Histopathologic evaluation of atypical neurofibromatous tumors and their transformation into malignant peripheral nerve sheath tumor in patients with neurofibromatosis 1—a consensus overview

Patients with neurofibromatosis 1 (NF1) develop multiple neurofibromas, with 8% to 15% of patients experiencing malignant peripheral nerve sheath tumor (MPNST) during their lifetime. Prediction of transformation, typically from plexiform neurofibroma, is clinically and histologically challenging. In this overview, after a consensus meeting in October 2016, we outline the histopathologic features and molecular mechanisms involved in the malignant transformation of neurofibromas. Nuclear atypia alone is generally insignificant. However, with atypia, loss of neurofibroma architecture, high cellularity, and/or mitotic activity >1/50 but <3/10 high-power fields, the findings are worrisome for malignancy. We propose the term "atypical neurofibromatous neoplasms of uncertain biologic potential (ANNUBP)" for lesions displaying at least 2 of these features. This diagnosis should prompt additional sampling, clinical correlation, and possibly, expert pathology consultation. Currently, such tumors are diagnosed inconsistently as atypical neurofibroma or low-grade MPNST. Most MPNSTs arising from neurofibromas are high-grade sarcomas and pose little diagnostic difficulty, although rare nonnecrotic tumors with 3-9 mitoses/10 high-power fields can be recognized as low-grade variants. Although neurofibromas contain numerous S100 protein/SOX10-positive Schwann cells and CD34-positive fibroblasts, both components are reduced or absent in MPNST. Loss of p16/CDKN2A expression, elevated Ki67 labeling, and extensive nuclear p53 positivity are also features of MPNST that can to some degree already occur in atypical neurofibromatous neoplasms of uncertain biologic potential. Complete loss of trimethylated histone 3 lysine 27 expression is potentially more reliable, being immunohistochemically detectable in about half of MPNSTs. Correlated clinicopathological, radiologic, and genetic studies should increase our understanding of malignant transformation in neurofibromas, hopefully improving diagnosis and treatment soon.

Methylation-based classification of benign and malignant peripheral nerve sheath tumors

The vast majority of peripheral nerve sheath tumors derive from the Schwann cell lineage and comprise diverse histological entities ranging from benign schwannomas and neurofibromas to high-grade malignant peripheral nerve sheath tumors (MPNST), each with several variants. There is increasing evidence for methylation profiling being able to delineate biologically relevant tumor groups even within the same cellular lineage. Therefore, we used DNA methylation arrays for methylome- and chromosomal profile-based characterization of 171 peripheral nerve sheath tumors. We analyzed 28 conventional high-grade MPNST, three malignant Triton tumors, six low-grade MPNST, four epithelioid MPNST, 33 neurofibromas (15 dermal, 8 intraneural, 10 plexiform), six atypical neurofibromas, 43 schwannomas (including 5 NF2 and 5 schwannomatosis associated cases), 11 cellular schwannomas, 10 melanotic schwannomas, 7 neurofibroma/schwannoma hybrid tumors, 10 nerve sheath myxomas and 10 ganglioneuromas. Schwannomas formed different epigenomic subgroups including a vestibular schwannoma subgroup. Cellular schwannomas were not distinct from conventional schwannomas. Nerve sheath myxomas and neurofibroma/schwannoma hybrid tumors were most similar to schwannomas. Dermal, intraneural and plexiform neurofibromas as well as ganglioneuromas all showed distinct methylation profiles. Atypical neurofibromas and low-grade MPNST were indistinguishable with a common methylation profile and frequent losses of CDKN2A. Epigenomic analysis finds two groups of conventional high-grade MPNST sharing a frequent loss of neurofibromin. The larger of the two groups shows an additional loss of trimethylation of histone H3 at lysine 27 (H3K27me3). The smaller one retains H3K27me3 and is found in spinal locations. Sporadic MPNST with retained neurofibromin expression did not form an epigenetic group and most cases could be reclassified as cellular schwannomas or soft tissue sarcomas. Widespread immunohistochemical loss of H3K27me3 was exclusively seen in MPNST of the main methylation cluster, which defines it as an additional useful marker for the differentiation of cellular schwannoma and MPNST.

Spatially- and temporally-controlled postnatal p53 knockdown cooperates with embryonic Schwann cell precursor Nf1 gene loss to promote malignant peripheral nerve sheath tumor formation.

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive sarcomas that arise sporadically or in association with the Neurofibromatosis type 1 (NF1) cancer predisposition syndrome. In individuals with NF1, MPNSTs are hypothesized to arise from Nf1-deficient Schwann cell precursor cells following the somatic acquisition of secondary cooperating genetic mutations (e.g., p53 loss). To model this sequential genetic cooperativity, we coupled somatic lentivirus-mediated p53 knockdown in the adult right sciatic nerve with embryonic Schwann cell precursor Nf1 gene inactivation in two different Nf1 conditional knockout mouse strains. Using this approach, ∼60% of mice with Periostin-Cre-mediated Nf1 gene inactivation (Periostin-Cre; Nf1flox/flox mice) developed tumors classified as low-grade MPNSTs following p53 knockdown (mean, 6 months). Similarly, ∼70% of Nf1+/− mice with GFAP-Cre-mediated Nf1 gene inactivation (GFAP-Cre; Nf1flox/null mice) developed low-grade MPNSTs following p53 knockdown (mean, 3 months). In addition, wild-type and Nf1+/− mice with GFAP-Cre-mediated Nf1 loss develop MPNSTs following somatic p53 knockout with different latencies, suggesting potential influences of Nf1+/− stromal cells in MPNST pathogenesis. Collectively, this new MPNST model system permits the analysis of somatically-acquired events as well as tumor microenvironment signals that potentially cooperate with Nf1 loss in the development and progression of this deadly malignancy.

Synchronous Malignant Peripheral Nerve Sheath Tumor and Adenocarcinoma of the Prostate: Case Report and Literature Review.

Malignant Peripheral Nerve Sheath Tumors (MPNSTs) of the prostate are extremely rare. A very unusual case of simultaneous adenocarcinoma and MPNST of the prostate is reported. A 60-year-old Caucasian male presented for annual urologic examination. Digital rectal examination revealed a painless, toughish, and asymmetrically enlarged prostate. Serum prostate-specific antigen was 1 ng/mL. Radiologic examinations demonstrated a large mass, which was arising from the left peripheral lobe of the prostate. The patient underwent transrectal ultrasound-guided biopsy of the prostate which revealed a smooth muscle tumor of uncertain malignant potential. Radical retropubic prostatectomy with en bloc removal of the mass and the seminal vesicles was performed and histology demonstrated low-grade MPNST and adenocarcinoma of the prostate. To the best of our knowledge, this is the first report of simultaneous prostatic adenocarcinoma and MPNST in the English literature.

Malignant Epithelioid Peripheral Nerve Sheath Tumor With Prominent Reticular/Microcystic Pattern in a Child

Malignant peripheral nerve sheath tumors (MPNSTs) constitute <2% of soft tissue neoplasms in children and display a wide histologic spectrum including low-grade and epithelioid variants, although most are high-grade spindle cell sarcomas. Here, we describe an unusual case of a large retroperitoneal epithelioid MPNST diagnosed in a 7-year-old girl without family history or clinical features of neurofibromatosis type 1. The patient was treated by repeated surgical interventions, polychemotherapy, autologous stem cell transplantation, and irradiation therapy. Over the years, she developed multiple disseminated abdominal recurrences but is currently alive with very slowly progressing disseminated intra-abdominal disease 18 years from initial diagnosis. Histologically, the tumor was composed of medium-sized polygonal and ovoid-to-spindled cells set within a copious myxoid matrix with a prominent reticular and microcystic pattern reminiscent of the recently described reticular/microcystic schwannoma. Immunohistochemistry revealed strong and diffuse expression of S100, CD56, CD57, collagen IV, and neuron-specific enolase, with negativity for perineurial cell markers (claudin-1, epithelial membrane antigen, and glucose transporter-1) and other lineage-specific mesenchymal and epithelial antigens. This unusual variant of low-grade MPNST must be differentiated from a variety of other entities, in particular benign perineurioma, myxoid neurofibroma, and benign reticular/microcystic schwannoma. Confinement of the recurrent disease to the abdominal cavity emphasizes the necessity of primary curative wide excision of this highly recurring but nonmetastasizing low-grade neoplasm.

The effect of surgical margins on outcomes for low grade MPNSTs and atypical neurofibroma.

While convention defines atypical neurofibroma as benign and low-grade malignant peripheral nerve sheath tumors (MPNSTs) as malignant, sparse outcomes data exist for these tumors. This study reviews clinical outcomes of surgically resected low-grade MPNST and atypical neurofibroma, focusing on the effect of surgical margins on outcome. This study is a retrospective review of 23 patients who underwent surgical resection of a low-grade MPNST or atypical neurofibroma. Treatment characteristics of adjuvant therapy and surgical margin were noted. Endpoints of local recurrence, presence of metastatic disease, disease-specific survival, and overall survival were reviewed. Eighteen of 23 patients (78%) had microscopically positive margins on the resection. Disease-specific survival was 100% for both atypical neurofibroma patients and those with low-grade MPNST, regardless of surgical margin. Local recurrence in terms of recurrence of measureable disease occurred in 2/12 (16.7%) of LGMPNST patients and 1/11 (9.1%) of atypical NF patients, all of whom had microscopically positive surgical margins. In a study dedicated exclusively to "intermediate" nerve sheath tumors, no patients developed metastatic disease nor died of disease despite a high rate of microscopically positive surgical margins (78%). While positive margins did lead to increased rates of local recurrence, these data suggest that surgeons potentially can temper their zeal for negative surgical margins in the setting of low-grade MPNST and atypical neurofibroma, as surgical morbidity may be more important than a presumed survival benefit of wide resection.

Superficial malignant peripheral nerve sheath tumor arising from diffuse neurofibroma in a neurofibromatosis type 1 patient

Malignant peripheral nerve sheath tumors (MPNST) are regarded as sarcomas that arise from peripheral nerves or that display differentiation along the lines of the various elements of the nerve sheath. These tumors occur in deep soft tissues, but superficial primary MPNST with a cutaneous or subcutaneous origin have rarely been reported. A 70-year-old woman presented with a 3-4-year history of a slowly enlarging soft nodule on the left side of her neck. The histopathological diagnosis of the nodule was low-grade MPNST arising from diffuse neurofibroma. There was increased cellularity, but no necrosis or mitotic activity. These histopathological findings pose difficulties in differential diagnosis from a neurofibroma with atypical histological features. We report a rare case of superficial MPNST arising from diffuse neurofibroma associated with underlying occipital bone dysplasia in a neurofibromatosis type 1 patient.

Fibroblastic Low-Grade Malignant Peripheral Nerve Sheath Tumor in the Orbit

Malignant peripheral nerve-sheath tumors (MPNSTs) are rare, poorly defined spindle cell sarcomas, and they are accompanied by heterologous elements in some cases. Among them, a fibroblastic element is one of the rarest and has been mentioned in some organs in several publications, but not in the orbit. The authors report a case of fibroblastic low-grade MPNSTs in the orbit. The mass was removed surgically, and the patient has been under close observation without evidence of disease recurrence for 2 years.

Malignant Peripheral Nerve Sheath Tumor of the Neck: Transformation From a Recurrent Neurofibroma in a Patient Without Neurofibromatosis

Malignant peripheral nerve sheath tumor (MPNST) is a rare tumor that is one of the most aggressive malignant lesions in the head and neck area. The majority of MPNSTs arise de novo or from malignant transformation of pre-existing neurofibromas, particularly in individuals with neurofibroma-tosis type 1 (NF1). However, solitary neurofibromas without an association with NF1 seldom recur after excision and rarely develop malignant changes. We present a 70-year-old man with a recurrent neurofibroma of the right side of the neck which transformed to low-grade MPNST after multiple excisions. The patient had no cutaneous features or family history consistent with NF1. Progression from a recurrent sporadic neurofibroma to malignancy is an extremely rare event and we found only two case reports in the literature. Any recurrent mass at the site of an excised neurofibroma or a rapidly enlarging, painful swelling of antecedent lesions should prompt consideration of MPNST.