Search Results (88)

Background/Objectives: MEK inhibitors (selumetinib, mirdametinib) are the only approved class of targeted therapy for neurofibromatosis type 1 (NF1)-associated plexiform neurofibroma (PN), producing partial responses in a substantial proportion of patients (up to 63.6% in adults; objective response rate 19.7% versus 5.4% with placebo in the KOMET trial). Responses, however, are rarely complete or durable, and in malignant peripheral nerve sheath tumor (MPNST) single-agent MEK inhibition is clinically ineffective. Mechanisms of escape from MEK inhibition in these tumors remain poorly characterized and are reported in the literature as isolated primary studies without an integrative analysis. The aim of this review was to systematize both the established molecular mechanisms of resistance to MEK inhibitors in PN and MPNST and the biologically plausible candidate mechanisms extrapolated from other RAS-driven malignancies. Methods: This is a narrative review. A structured search was performed in PubMed, PubMed Central, NCBI Bookshelf, and Scopus, supplemented by clinical practice guidelines and regulatory documents; it covered publications up to 31 May 2026 and was updated in August 2026. Ninety-six sources are cited, and their composition by publication type is reported; record counts at the intermediate screening steps were not maintained, and no PRISMA flow diagram is presented. Results: Mechanisms were classified within a convergent framework into six categories: reactivation of MAPK signaling within the cascade; parallel (bypass) reactivation through receptor tyrosine kinases and adjacent inputs; epigenetic and transcriptional rewiring; cell survival programs; the tumor microenvironment and immune evasion; and intratumoural heterogeneity. Each mechanism was then graded along two independent axes—the strength of evidence that it confers resistance in PN or MPNST (E1–E3) and its therapeutic tractability (T1–T3)—and annotated with the entity and model constituting its evidence source. Conclusions: Resistance to MEK inhibition in PN and MPNST is convergent rather than mechanism-unique. The principal limitation of the field is the near-absence of clinical resistance data from patients progressing on MEK inhibitors; prospective molecular monitoring, rational combination trials, and mechanism-stratifying biomarkers are the priorities. Full article

Background/Objectives: Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder caused by pathogenic variants in the NF1 gene, characterized by high phenotypic variability. Methods: We present clinical and molecular data from a Romanian cohort of 54 patients initially diagnosed clinically. Results: Phenotypic evaluation (n = 54) revealed a high prevalence of café-au-lait macules (100%), Lisch nodules (64.8%), axillary/inguinal freckling (61.1%), and cutaneous neurofibromas (42.6%). Due to financial constraints (genetic testing not covered by the national health system), molecular confirmation by next-generation sequencing (NGS) was possible in only 12 patients (mostly sporadic cases and young children). Genetic testing identified a diverse spectrum of variants, including frameshift (41.7%, n = 5), nonsense (33.3%, n = 4), missense (16.7%, n = 2), and one splicing deletion (8.3%, n = 1). A novel complex NF1 frameshift variant, c.7504_7508delinsC (p.Ser2502Argfs*24) in exon 54, was identified in a patient exhibiting an aggressive phenotype characterized by plexiform neurofibromas, a malignant peripheral nerve sheath tumor (MPNST), and severe skeletal abnormalities. Additionally, a recurrent nonsense variant, NF1 c.910C>T (p.Arg304*), was detected in two unrelated individuals. Conclusions: The high proportion of sporadic cases (58.3%) in the molecularly tested subgroup underscores the critical role of early genetic screening. By integrating clinical data from 54 patients with the first molecular characterization of NF1 in Romania, this study expands the mutational spectrum and provides preliminary, descriptive insights into genotype–phenotype correlations. It also proposes a cost-effective diagnostic algorithm adapted for resource limited settings and lays the groundwork for future multicenter initiatives. Given the exploratory nature of the molecular subgroup (n = 12), all genotype–phenotype observations require validation in larger independent cohorts. Full article

Background: Malignant peripheral nerve sheath tumors (MPNSTs) are deadly sarcomas that arise from Schwann cells and lack effective therapies. RABL6A is an oncogenic Rab-like GTPase whose expression is associated with worse survival in many human cancers. It is required for human MPNST cell survival, and its expression is dramatically increased in patient MPNSTs compared to benign precursor lesions. Methods: To model elevated expression of RABL6A in vivo, we developed transgenic mice expressing Cre-inducible Rabl6a. These Rabl6a-tg mice express the murine Rabl6a cDNA with a 5′ hemagglutinin [HA] epitope sequence downstream of a CMV enhancer and separated by a lox–stop–lox cassette. Double transgenic DhhCre; Rabl6a-tg mice were generated to achieve Schwann-cell specific Cre expression from the Desert hedgehog (Dhh) promoter. De novo MPNSTs were induced by CRISPR editing of Nf1, Ink4a, and Arf genes in the mouse sciatic nerve. Results: Cre-dependent expression of transgenic Rabl6a was verified at the mRNA and protein levels in Cre-positive mouse embryo fibroblasts and tissues. Increased Rabl6a expression in DhhCre; Rabl6a-tg mice had no effect on de novo MPNST initiation but significantly accelerated tumor progression relative to DhhCre control mice. The Rabl6a phenotype was associated with increased tumor angiogenesis but not proliferation. Interestingly, many MPNSTs in the DhhCre background exhibited varying levels of rhabdomyoblastic (RMB) features. That immature muscle cell phenotype is a hallmark of malignant Triton tumors, a rare histological variant of human MPNSTs associated with worse outcomes. Conclusions: These data provide direct evidence that Rabl6a is a functional driver of MPNSTs while establishing Rabl6a-tg mice as a suitable model for investigating Rabl6a’s role in other lethal RABL6A-high tumors. Full article

Neurofibromatosis type 1 (NF1) is a genetic tumor predisposition syndrome characterized by a substantial risk of developing peripheral nerve sheath tumors, including malignant peripheral nerve sheath tumors (MPNSTs), which occur in 8–13% of patients. Approximately 50% arise from plexiform neurofibromas (PNs) and 40% develop de novo, making them a major cause of premature mortality. Current clinical management is limited by the intrinsic shortcomings of standard imaging modalities: magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT), and tissue biopsy in distinguishing benign PNs from early malignant transformation, which remains a major clinical challenge. This progression follows a stepwise molecular continuum marked by cumulative genetic alterations and widespread epigenetic dysregulation. In this setting, liquid biopsy has emerged as a promising non-invasive approach to help fill these diagnostic gaps by enabling real-time molecular monitoring through the analysis of circulating tumor DNA (ctDNA) and other blood-based biomarkers. This review examines the current evidence supporting liquid biopsy applications in NF1 management, including early detection of MPNST, discrimination between benign and malignant lesions, mutational profiling for therapeutic targeting, and disease monitoring before and during treatment. We also discuss the current evidence on fragmentomics, methylomics and driver mutation profiling as tools to distinguish PNs from MPNSTs. Recent evidence suggests that liquid biopsy may help detect molecular changes associated with malignant transformation before clear clinical signs emerge, potentially opening an important window for intervention and supporting a shift towards a more molecularly informed surveillance model. Finally, this review considers the possible extension of liquid biopsy to other tumor types, including NF1-deficient breast cancer, and outlines a future management framework aimed at improving early diagnosis and personalized therapeutic intervention in this high-risk population. Full article

Background: Peripheral nerve sheath tumors of the oral cavity are rare and encompass both benign and malignant entities. Differentiating between these lesions remains challenging due to overlapping clinical and histopathological characteristics. Case presentation: We present two cases illustrating the biological spectrum of peripheral nerve sheath tumors in the oral cavity. The first case involves a 76-year-old male with a recurrent lower lip lesion initially diagnosed as benign, which progressed to a high-grade malignant peripheral nerve sheath tumor (MPNST). The second case describes a 20-year-old male presenting with a nodular lesion of the tongue, initially suspected to be reactive following trauma, but histologically confirmed as a benign schwannoma. Both patients underwent surgical treatment with favorable immediate postoperative outcomes. Conclusions: These cases highlight the diagnostic complexity and heterogeneous behavior of peripheral nerve sheath tumors. Histopathological and immunohistochemical evaluations are essential for definitive diagnosis. Clinicians should maintain a high index of suspicion and consider possible association with NF1 or schwannomatosis, particularly in recurrent or atypical lesions. Full article

Background/Objectives: This prospective study used a standardized preoperative assessment to characterize the full spectrum of pain in patients with peripheral nerve tumors, addressing the lack of structured pain phenotyping in this population. Methods: Between June 2024 and October 2025, preoperative pain symptoms were assessed in 91 patients, representing 16% of the Peripheral Nerve Tumor Registry (PNTR) cohort, using the PainDETECT questionnaire (0–38) at two centers: University Hospital Ulm, Günzburg (n = 72), and University Hospital Essen (n = 19). Results: Ninety-one patients (61.5% male; mean age, 49 years) were included. Most tumors were located in the lower extremity (54.9%). PainDETECT scores were ≤12 in 51.6%, 13–18 in 24.1%, and ≥19 in 21.9% of patients. Malignant tumors (6.5%) had the highest mean score (17), but benign tumors also showed a relevant pain burden (mean 11.9). Hybrid peripheral nerve sheath tumors and neurofibromas had numerically higher mean scores than schwannomas, although the difference was not statistically significant. Pain severity was not associated with tumor size, depth, or affected nerve. The most common sensory features were electric-shock-like and pressure-related pain, as reflected by a positive Tinel sign in 86.8% of patients. The most frequent pain pattern was intermittent attacks with pain-free intervals (46%). Conclusions: These interim results indicate that pain is common even in benign peripheral nerve tumors, challenging the assumption that these lesions are often asymptomatic. Malignant tumors showed the highest pain scores. The heterogeneous pain phenotypes highlight the need for individualized assessment and management. Expansion to a multicenter evaluation within the framework of the PNTR is planned. Full article

Introduction: Soft tissue sarcomas (STS) exhibit profound molecular heterogeneity. While recurrent gene fusions hold significant diagnostic and therapeutic value—guiding treatment selection and identifying novel molecular targets—our understanding of their broader clinical implications remains limited. Materials and Methods: We performed next-generation sequencing (NGS; FusionPlex Sarcoma v2, Archer™) and bioinformatic analysis (STAR v.2.7, Arriba) on formalin-fixed paraffin-embedded (FFPE) core needle biopsy specimens. The cohort consisted of patients enrolled in a phase II clinical trial (NCT03651375) who received preoperative chemoradiotherapy according to the UNRESARC protocol. Results: The analysed cohort comprised nine adult patients (median age 66 years; range 44–73) diagnosed with undifferentiated pleomorphic sarcoma (UPS; n = 3), malignant peripheral nerve sheath tumour (MPNST; n = 3), myxofibrosarcoma (MFS; n = 2), and leiomyosarcoma (LMS; n = 1), predominantly high-grade (G3; 5/9) and extremity-localised (6/9). Gene fusions were detected in one-third of patients (3/9), exclusively in G3 tumours. Specifically, we identified an SGSH-PRKCA fusion in MFS (thigh), a LINC01133-OGA fusion in MPNST (thorax), and a concurrent JAZF1-MYH7B (chr7:27995037 intronic-chr20:33563203 exon/splice-site, out-of-frame but preserving myosin domains) with a PRKCA-associated intergenic rearrangement (chr1, retaining C1/kinase domains) in UPS (upper back). Notably, the SGSH-PRKCA and JAZF1-MYH7B pairs have not been previously described in the literature for these STS subtypes. Fusion-positive (F1) cases showed stable radiological disease (RECIST 1.1 SD) and EORTC C/D pathological responses with 5–20% residual viable tumour, whereas fusion-negative (F0) cases showed a wider range of radiological and pathological outcomes, including partial response, progression, and stable disease. Conclusions: Our analysis suggests that broad genomic profiling may provide complementary molecular information in diagnostically challenging cases managed at specialised sarcoma centres, particularly when morphology and immunohistochemistry are insufficient. In the present series, however, the detected rearrangements did not alter systemic treatment, and the data do not support claims of prognostic, predictive, or therapeutic actionability. Full article

Plexiform neurofibromas associated with neurofibromatosis type I (pNF1s) are benign tumors caused by the complete loss of function of the NF1 gene, which encodes a negative regulator of the RAS/mitogen-activated protein kinase (MAPK) pathway. pNF1s carry a significant risk of progression to malignant peripheral nerve sheath tumors (MPNSTs), which are highly aggressive and largely incurable. FDA-approved mitogen-activated protein kinase kinase (MEK) inhibitors, selumetinib and mirdametinib, have shown ~30% tumor shrinkage in 70% and 42% pNF1 patients, respectively. However, not all pNF1s respond to MEK inhibition, and treatment is often associated with adverse effects such as dermatologic and gastrointestinal toxicities, underscoring the need for improved therapeutic strategies with minimal side effects. Here, we demonstrate that prolonged MEK inhibition increases proteolytic activity in 3D pNF1 tumor structures, consistent with enhanced extracellular matrix degradation. Prolonged treatment with four mechanistically and chemically distinct MEK inhibitors consistently reduced ERK phosphorylation, a downstream effector of the RAS/MAPK pathway, yet induced adaptive phosphorylation of MEK and AKT in pNF1 tumor cells. Phosphorylation of MEK is required for its catalytic activation and subsequent phosphorylation of ERK. Increased MEK phosphorylation in the presence of MEK inhibitors reflects upstream pathway reactivation but does not lead to ERK phosphorylation and activation because of the presence of the inhibitor. This response was also observed in MPNST cell lines treated with MEK inhibitors. These findings suggest that adaptive activation of upstream and parallel survival pathways may counteract the intended effects of MEK inhibition and support the rationale for combination strategies to improve therapeutic outcomes in NF1-associated tumors. Full article

Background/Objectives: Neurofibromatosis Type 1 (NF1) is a genetic syndrome caused by pathogenic NF1 variants encoding neurofibromin, a Ras GTPase activating protein. Individuals with NF1 develop peripheral nerve sheath tumors called neurofibromas. Approximately 50% of NF1 patients develop plexiform neurofibromas (pNFs) which have up to 13% lifetime risk of transformation into malignant peripheral nerve sheath tumors (MPNSTs). Current therapeutic strategies emphasize surgical resection with wide margins, radiation, and traditional chemotherapy for unresectable MPNSTs. However, NF1 patients diagnosed with MPNSTs have 5-year survival rates as low as 16%. The two recently FDA-approved drugs for pNFs, the MEK inhibitors selumetinib and mirdametinib, are not used to prevent or treat MPNSTs. Methods: The MEK inhibitor trametinib and the dual HDAC/PI3K inhibitor fimepinostat were assessed for growth inhibitory effects in nine unique patient-derived MPNST cell lines, as both drugs have preclinical efficacy in other Schwann cell-derived tumors. Results: Trametinib, which is approved for malignant melanomas, promoted cell death in 7/9 MPNST cell lines with a geometric mean GI50 = 17 nM. When directly compared to selumetinib and mirdametinib in a subset of four MPNST cell lines, trametinib had the lowest mean GI50 (trametinib = 38 nM, mirdametinib = 1.6 µM, selumetinib = 4.9 µM). Trametinib was also superior to selumetinib and mirdametinib in blocking ERK1/2 phosphorylation for 24 h. Fimepinostat promoted cell death in all cell lines with a geometric mean GI50 = 17 pM. Conclusions: These studies demonstrate in vitro efficacy for two candidate MPNST therapeutics which could reduce tumor burden and metastasis in NF1 patients. Full article

Neurofibromatosis type 1 (NF1) predisposes to a spectrum of peripheral nerve sheath tumors, ranging from benign plexiform neurofibromas (PN) to atypical neurofibromatous neoplasms of uncertain biological potential (ANNUBP) and malignant peripheral nerve sheath tumors (MPNST). Tumorigenesis follows a multistep molecular cascade initiated by biallelic NF1 inactivation, followed by CDKN2A loss and disruption of the Polycomb Repressive Complex 2 (PRC2). These events guide chromatin remodeling, widespread epigenetic dysregulation, and activation of oncogenic pathways such as RAS/MAPK and PI3K/AKT. Here, we integrate genomic, transcriptomic, and epigenomic studies to delineate the molecular trajectories underlying tumor progression and to define promising biomarkers for the early detection of malignant transformation. Emerging liquid biopsy approaches, based on circulating tumor DNA (ctDNA) analyses, reveal distinctive copy number variations (CNVs) and methylation patterns that mirror tissue-derived profiles, enabling the detection of malignant transformation. Together, these findings support a model in which cumulative genetic and epigenetic alterations drive the PN–ANNUBP–MPNST continuum. They also underscore the value of multi-omics and liquid biopsy-based strategies to improve early diagnosis, patient risk stratification, and personalized management of NF1-associated tumors, thereby advancing precision medicine in this complex disease spectrum. Full article

Background/Objectives High-resolution nerve ultrasound (HRUS) is a promising imaging modality in patients with neurofibromatosis type 1 (NF1). The aim of this study was to evaluate the use of HRUS in adults with NF1 by assessing changes in HRUS findings over a two-year follow-up time and reporting interobserver variability. Methods Sixty adult patients with NF1 were invited for a study visit including a clinical examination, nerve conduction studies (NCSs) and HRUS, at baseline and after two-years follow-up. The nerve cross-sectional area (CSA) was measured at standard anatomical sites and at additional sites in cases of nerve enlargements. In 16 patients, the CSA measurements of the median nerve on one side were performed by two observers to assess interobserver variability. Results Fifty-two patients participated in the follow-up visit. During follow-up, 40% of nerve enlargements increased, 46% decreased and 14% remained stable. Especially larger CSA measurements at baseline showed substantial increases and decreases at follow-up. The presence or absence of plexiform neurofibromas remained the same. Interobserver agreement of median nerve CSA measurements with HRUS was 0.982 (95% CI: 0.969–0.99). Conclusions HRUS can be an important additional imaging tool in patients with NF1. It is helpful to distinguish between patients with and without plexiform neurofibromas, which is relevant for estimating the risk of developing malignant peripheral nerve sheath tumors (MPNSTs). The good interobserver agreement supports the use of HRUS in clinical practice. The majority of nerve enlargements decreased spontaneously in size within two years, which limits the reliability of tumor volume as sole marker for treatment response. Full article

Neurofibromatosis type 1 (NF1) is an inherited, autosomal dominant syndrome that affects about 1 in every 3000 people worldwide. Early tumor detection is crucial for surveillance and intervention, especially given the potential for serious complications, including visual impairment, skeletal deformities, and malignancy. Therefore, it is essential for pediatricians and other healthcare professionals who provide care to these patients to be aware of all signs, treatments, and management strategies to deliver the best possible care. This study aims to develop a consensus for the diagnosis, treatment, and management of benign and malignant tumors associated with pediatric patients with NF1. Delphi methodology was used to achieve consensus among experts on the diagnostic accuracy, therapeutic efficacy, safety, and surveillance of pediatric patients with NF1. The consensus made 24 recommendations: gliomas in the optic pathway—6 statements, non-optical gliomas—2 statements, plexiform neurofibromas—5 statements, malignant peripheral nerve sheath tumors (MPNST)—6 statements, melanoma—1 statement, juvenile myelomonocytic leukemia (JMML)—1 statement, pheochromocytoma and paraganglioma—2 statements, and gastrointestinal stromal tumors (GIST)—1 statement. This consensus represents the first Brazilian recommendations on malignant and benign tumors in pediatric patients with NF1, providing a framework to standardize and optimize the clinical application for this disease. Full article

Mutations in the NF1 gene cause Neurofibromatosis Type 1 (NF1), one of the most common genetic disorders. This gene encodes neurofibromin, a member of the GTPase-activating protein (GAP) family that functions as a negative regulator of RAS signaling. Loss of NF1 function leads to persistent RAS activation and promotes tumor growth. The clinical manifestations of NF1 mainly include pigmentary changes, benign and malignant peripheral nerve sheath tumors, as well as gliomas affecting the central nervous system. Currently, MEK inhibition is the only approved therapy and is primarily effective in controlling plexiform neurofibromas (pNFs). However, more comprehensive treatments are needed to address the full spectrum of NF1 manifestations and malignant transformation. Novel therapeutic strategies, including AAV-based gene therapy aimed at restoring NF1 function, oncolytic herpes simplex virus (oHSV) therapy targeting RAS-dysregulated tumor cells, and chimeric antigen receptor T cell (CAR-T) therapy targeting NF1-associated tumors, are under active investigation. In this review, we explore the genetic mechanisms underlying NF1 and highlight recent advances in therapeutic development with a special focus on AAV-based gene therapies alongside other approaches with recent clinical and translational advancements. Full article

Malignant peripheral nerve sheath tumors (MPNSTs) are one of the most difficult sarcomas to treat. Due to the rarity of MPNSTs, many of the therapeutic approaches used are from treatment guidelines for soft tissue sarcoma. Besides surgery, little success has been achieved using these therapies. Traditional chemotherapy and radiation therapy regimens designed to treat sarcoma have unclear efficacy when used to treat MPNSTs. Targeted therapeutics that succeeded in other sarcomas failed to produce positive results in MPNSTs. Moreover, investigational agents that have shown efficacy in preclinical models have produced disappointing outcomes in clinical trials. While therapeutic options for patients with MPNST have remained relatively stagnant, dramatic improvements in therapeutic outcomes of other rare sarcomas have been made. This difference in success is likely caused by the complex heterogeneity of MPNSTs that hinders drug development, although many MPNSTs are associated with neurofibromatosis type 1 (NF1), a genetic disorder resulting from mutations in the NF1 gene that encodes the negative RAS regulator neurofibromin. The development of new agents for MPNST treatment has shifted away from solely targeting RAS pathway gene products to stimulating the immune system and manipulating other MPNST driver mutations such as CDKN2A/B, SUZ12, EED, and TP53. This review presents recent advances in the treatment of sarcomas and the future of drug development targeting MPNSTs. Full article

Malignant peripheral nerve sheath tumors (MPNSTs) are rare sarcomas with an extremely rare perineurial subtype. Herein, we present a case of a perineurial MPNST in the cauda equina. Clinically and radiologically, a mass extending from within the spinal canal at the L5 level to outside the intervertebral foramen was identified, raising suspicion of a neurogenic tumor as the primary diagnosis. Computed tomography-guided biopsy suggested an intermediate- to low-grade malignancy; however, a definitive diagnosis could not be established. Two years later, worsening neurological symptoms prompted further imaging, which revealed significant tumor growth and bone invasion. Open biopsy was performed to obtain a definitive diagnosis of perineurial MPNST. MPNSTs lack distinctive imaging features and are generally diagnosed based on a combination of radiological and histopathological findings. Although MPNSTs have a poor prognosis, the perineurial subtype is considered to have a relatively favorable outcome. Given these factors, early diagnosis followed by surgical resection or radiation therapy is recommended. Full article