Loss of H3K27 tri-methylation is a diagnostic marker for malignant peripheral nerve sheath tumors and an indicator for an inferior survival

Polycomb repression regulates Schwann cell proliferation and axon regeneration after nerve injury

The transition of differentiated Schwann cells to support of nerve repair after injury is accompanied by remodeling of the Schwann cell epigenome. The EED-containing polycomb repressive complex 2 (PRC2) catalyzes histone H3K27 methylation and represses key nerve repair genes such as Shh, Gdnf, and Bdnf, and their activation is accompanied by loss of H3K27 methylation. Analysis of nerve injury in mice with a Schwann cell-specific loss of EED showed the reversal of polycomb repression is required and a rate limiting step in the increased transcription of Neuregulin 1 (type I), which is required for efficient remyelination. However, mouse nerves with EED-deficient Schwann cells display slow axonal regeneration with significantly low expression of axon guidance genes, including Sema4f and Cntf. Finally, EED loss causes impaired Schwann cell proliferation after injury with significant induction of the Cdkn2a cell cycle inhibitor gene. Interestingly, PRC2 subunits and CDKN2A are commonly co-mutated in the transition from benign neurofibromas to malignant peripheral nerve sheath tumors (MPNST's). RNA-seq analysis of EED-deficient mice identified PRC2-regulated molecular pathways that may contribute to the transition to malignancy in neurofibromatosis.

Inferior survival for patients with malignant peripheral nerve sheath tumors defined by aberrant TP53

Malignant peripheral nerve sheath tumor is a rare and aggressive disease with poor treatment response, mainly affecting adolescents and young adults. Few molecular biomarkers are used in the management of this cancer type, and although TP53 is one of few recurrently mutated genes in malignant peripheral nerve sheath tumor, the mutation prevalence and the corresponding clinical value of the TP53 network remains unsettled. We present a multi-level molecular study focused on aberrations in the TP53 network in relation to patient outcome in a series of malignant peripheral nerve sheath tumors from 100 patients and 38 neurofibromas, including TP53 sequencing, high-resolution copy number analyses of TP53 and MDM2, and gene expression profiling. Point mutations in TP53 were accompanied by loss of heterozygosity, resulting in complete loss of protein function in 8.2% of the malignant peripheral nerve sheath tumors. Another 5.5% had MDM2 amplification. TP53 mutation and MDM2 amplification were mutually exclusive and patients with either type of aberration in their tumor had a worse prognosis, compared to those without (hazard ratio for 5-year disease-specific survival 3.5, 95% confidence interval 1.78-6.98). Both aberrations had similar consequences on the gene expression level, as analyzed by a TP53-associated gene signature, a property also shared with the copy number aberrations and/or loss of heterozygosity at the TP53 locus, suggesting a common "TP53-mutated phenotype" in as many as 60% of the tumors. This was a poor prognostic phenotype (hazard ratio = 4.1, confidence interval:1.7-9.8), thus revealing a TP53-non-aberrant patient subgroup with a favorable outcome. The frequency of the "TP53-mutated phenotype" warrants explorative studies of stratified treatment strategies in malignant peripheral nerve sheath tumor.

Sarcomas of the Oral and Maxillofacial Region: Analysis of 26 Cases with Emphasis on Diagnostic Challenges

Sarcomas of the Oral and Maxillofacial Region (SOMR) are rare lesions which pose diagnostic and management challenges. We analyzed 26 cases of SOMR with respect to clinical presentation, histopathological subtype, treatment modalities, recurrence, and treatment outcome. In our series, Osteosarcoma (OS) was the most common type of sarcoma (7 cases), followed by 5 cases of Ewing's Sarcoma (ES), 3 cases each of Chondrosarcoma (CS) and Leiomyosarcoma (LMS), 2 cases each of Malignant Peripheral Nerve Sheath Tumor (MPNST), Pleomorphic Undifferentiated Sarcoma (PUS), Myeloid Sarcoma (MS)and Rhabdomyosarcoma (RMS). Surgery was the primary treatment modality in most cases and was combined with adjuvant chemo/ radiotherapy in few cases. 24 of the 26 cases were followed up for an average period of 40.67 months. Adverse disease outcomes like recurrence were seen in 2 cases whereas death due to the disease was reported in 7 cases. In view of the diagnostic challenges faced in SOMRs, it appears practical to stress on the underlying genetic aspects of the disease process rather than histological subtyping to improve disease outcome.

Applications of Ancillary Testing in the Cytologic Diagnosis of Soft Tissue Neoplasms

Soft tissue neoplasms are diagnostically challenging, although many advances in ancillary testing now enable accurate classification of fine-needle aspiration biopsies by detection of characteristic immunophenotypes (including protein correlates of molecular alterations) and molecular features. Although there are many useful diagnostic immunohistochemical markers and molecular assays, their diagnostic utility relies on correlation with clinical and morphologic features, judicious application, and appropriate interpretation because no single test is perfectly sensitive or specific. This review discusses applications of ancillary testing for commonly encountered soft tissue neoplasms in cytopathologic practice in the context of a pattern-based approach.

Recent Advances in the Diagnosis and Pathogenesis of Neurofibromatosis Type 1 (NF1)-associated Peripheral Nervous System Neoplasms

The diagnosis of a neurofibroma or a malignant peripheral nerve sheath tumor (MPNST) often raises the question of whether the patient has the genetic disorder neurofibromatosis type 1 (NF1) as well as how this will impact the patient's outcome, what their risk is for developing additional neoplasms and whether treatment options differ for NF1-associated and sporadic peripheral nerve sheath tumors. Establishing a diagnosis of NF1 is challenging as this disorder has numerous neoplastic and non-neoplastic manifestations which are variably present in individual patients. Further, other genetic diseases affecting the Ras signaling cascade (RASopathies) mimic many of the clinical features of NF1. Here, we review the clinical manifestations of NF1 and compare and contrast them with those of the RASopathies. We also consider current approaches to genetic testing for germline NF1 mutations. We then focus on NF1-associated neurofibromas, considering first the complicated clinical behavior and pathology of these neoplasms and then discussing our current understanding of the genomic abnormalities that drive their pathogenesis, including the mutations encountered in atypical neurofibromas. As several neurofibroma subtypes are capable of undergoing malignant transformation to become MPNSTs, we compare and contrast patient outcomes in sporadic, NF1-associated and radiation-induced MPNSTs, and review the challenging pathology of these lesions. The mutations involved in neurofibroma-MPNST progression, including the recent identification of mutations affecting epigenetic regulators, are then considered. Finally, we explore how our current understanding of neurofibroma and MPNST pathogenesis is informing the design of new therapies for these neoplasms.

High expression of EZH2 as a marker for the differential diagnosis of malignant and benign myogenic tumors

Overlap in morphologic features between malignant and benign myogenic tumors, such as leiomyosarcoma (LMS) vs. leiomyoma as well as rhabdomyosarcoma (RMS) vs. rhabdomyoma, often makes differential diagnosis difficult and challenging. Here the expressions of Enhancer of Zeste Homolog 2 (EZH2), Suppressor of Zeste 12 (SUZ12), retinoblastoma protein associated protein 46 (RbAp46), Embryonic Ectoderm Development (EED) and ki-67 protein were detected by immunohistochemistry to evaluate their values in differential diagnosis. The expression of EZH2 mRNA was investigated by analyzing the Gene Expression Omnibus Datasets. The results demonstrated that EZH2 protein was detected in 81.25% (26/32) of LMS and 70.58% (36/51) of RMS, whereas none of leiomyoma (n = 16), rhabdomyoma (n = 15) and normal tissues (n = 31) showed positive immunostaining (p < 0.05). EZH2 protein was found to have a sensitivity of 91.30% and specificity of 100% in distinguishing well-differentiated LMS from cellular leiomyoma, and a sensitivity of 92.86% and specificity of 100% in distinguishing well-differentiated embryonal rhabdomyosarcoma (ERMS) from fetal rhabdomyoma. Besides, the expression of EZH2 mRNA was higher in LMS and RMS than in benign tumors (p < 0.05). The expressions of SUZ12 and RbAp46 protein were higher in RMS than in rhabdomyoma (p < 0.05). Conclusively, the high expression of EZH2 is a promising marker in distinguishing well–differentiated LMS from cellular leiomyoma, or well–differentiated ERMS from fetal rhabdomyoma, and the upregulation of EZH2 protein expression may occur at transcriptional level.

Malignant progression of a peripheral nerve sheath tumor in the setting of rhabdoid tumor predisposition syndrome

Malignant progression of a benign or low-grade tumor in individuals with germline alteration of SMARCB1 gene is not well characterized. In a family in which two carrier children had germline SMARCB1 mutations and atypical teratoid rhabdoid tumor, we report malignant progression of a nerve sheath tumor over a 7-year period in an affected adult family member. Prompt identification of the germline SMARCB1 alteration and the resultant rhabdoid tumor predisposition syndrome can help guide genetic counseling and surveillance in affected family members.

Loss of histone H3K27me3 identifies a subset of meningiomas with increased risk of recurrence

Epigenetic patterns on the level of DNA methylation have already been shown to separate clinically relevant subgroups of meningiomas. We here set out to identify potential prognostic implications of epigenetic modification on the level of histones with focus on H3K27 trimethylation (H3K27me3). H3K27me3 was assessed by immunohistochemistry on 232 meningiomas from 232 patients. In 194 cases, trimethylation was detected in tumor cells. In 25 cases, staining was limited to vessels while all tumor cells were negative. Finally, 13 cases yielded equivocal staining patterns. Reduced abundance of H3K27me3 in cases with staining limited to vessels was confirmed by mass spectrometry on a subset of cases. Lack of staining for H3K27me3 in all tumor cells was significantly associated with more rapid progression (p = 0.009). In line, H3K27me3-negative cases were associated with a DNA methylation pattern of the more aggressive types among the recently introduced DNA methylation groups. Also, NF2 and SUFU mutations were enriched among cases with complete lack of H3K27me3 staining in tumor cells (p < 0.0001 and p = 0.029, respectively). H3K27me3 staining pattern added significant prognostic insight into WHO grade II cases and in the compound subset of WHO grade I and II cases (p = 0.04 and p = 0.007, respectively). However, it did not further stratify within WHO grade III cases. Collectively, these data indicate that epigenetic modifications beyond DNA methylation are involved in the aggressiveness of meningioma. It also suggests that H3K27me3 immunohistochemistry might be a useful adjunct in meningioma diagnostics, particularly for cases with WHO grade II histology or at the borderline between WHO grade I and II.

Advances in sarcoma diagnostics and treatment

The heterogeneity of sarcomas with regard to molecular genesis, histology, clinical characteristics, and response to treatment makes management of these rare yet diverse neoplasms particularly challenging. This review encompasses recent developments in sarcoma diagnostics and treatment, including cytotoxic, targeted, epigenetic, and immune therapy agents. In the past year, groups internationally explored the impact of adding mandatory molecular testing to histological diagnosis, reporting some changes in diagnosis and/or management; however, the impact on outcomes could not be adequately assessed. Transcriptome sequencing techniques have brought forward new diagnostic tools for identifying fusions and/or characterizing unclassified entities. Next-generation sequencing and advanced molecular techniques were also applied to identify potential targets for directed and epigenetic therapy, where preclinical studies reported results for agents active within the receptor tyrosine kinase, mTOR, Notch, Wnt, Hedgehog, Hsp90, and MDM2 signaling networks. At the level of clinical practice, modest developments were seen for some sarcoma subtypes in conventional chemotherapy and in therapies targeting the pathways activated by various receptor tyrosine kinases. In the burgeoning field of immune therapy, sarcoma work is in its infancy; however, elaborate protocols for immune stimulation are being explored, and checkpoint blockade agents advance from preclinical models to clinical studies.

Prognostic implications of polycomb proteins ezh2, suz12, and eed1 and histone modification by H3K27me3 in sarcoma

Background

Polycomb repressive complex 2 (PRC2; formed by EZH2, SUZ12, and EED protein subunits) and PRC1 (BMI1 protein) induce gene silencing through histone modification by H3K27me3. In the present study, we characterized the PRC expression pattern and its clinical implication in sarcoma.

Methods

Using immunohistochemistry, we analyzed PRC expression in 105 sarcoma patients with 5 subtypes: synovial sarcoma (n = 18), rhabdomyosarcoma (n = 28), Ewing sarcoma (n = 15), osteosarcoma (n = 30), and others (n = 14).

Results

The median age at diagnosis in the patient cohort was 26.8 years (range: 1–78 years) and the male-to-female ratio was 1:4. Initial disease presentation was locoregional disease in 83% of patients and initial metastatic disease in the remaining 17%. PRC expression was not significantly different according to histologic subtype (P = 0.400). Overall survival (OS) was significantly poor for SUZ12 ^high (P = 0.001), EED1 ^high (P = 0.279), and H3K27me3 ^high (P = 0.009). Ultimately, patients with PRC2^high had significantly inferior OS than the no expression group (P = 0.009). In the Cox proportional hazard model adjusted for stage, histologic grade, surgery, margin and initial metastasis, SUZ12 expression (P = 0.020, HR 29.069, 95% CI 1.690–500.007), H3K27me3 (P = 0.010, HR 3.743, 95% CI 1.370–10.228) expression was significantly associated with shorter OS.

Conclusion

We detected PRC expression in various sarcomas and demonstrated its independent negative prognostic role, suggesting the PRC axis as promising therapeutic target for treating sarcoma.

Contemporary Sarcoma Diagnosis, Genetics, and Genomics

Sarcomas include diverse mesenchymal neoplasms with widely varied prognosis, clinical behavior, and treatment. Owing to their rarity and histologic overlap, accurate diagnosis of sarcomas can be challenging. Our approach has evolved dramatically in the past few decades, where novel insights into the molecular pathogenetic basis for sarcomas has dramatically (re)shaped contemporary diagnosis, building on a largely morphology- and clinical presentation–based strategy. Examples include the introduction of novel immunohistochemical markers that serve as surrogates for molecular genetic alterations and identification of characteristic molecular alterations. Accordingly, cytogenetic and molecular genetic analyses, such as conventional karyotyping, fluorescence in situ hybridization, reverse transcription–polymerase chain reaction, and targeted sequencing, have increasingly been incorporated into the routine diagnostic work-up of these neoplasms. For those sarcomas with complex cytogenetic changes that lack specific alterations, additional testing is often directed toward identifying lines of differentiation and excluding pathognomonic (cyto-)genetic alterations. Although some gene rearrangements are diagnostic of particular sarcoma types, certain fusion partners, most notably EWSR1, are not tumor specific (and may, in fact, also be found in benign tumors). Correlation with clinical, radiologic, morphologic, and immunohistochemical findings is particularly important in tumors with such rearrangements to establish the correct diagnosis, acknowledging the inherent limitations of diagnostic tests. The recognition of sarcomas occurring in cancer predisposition syndromes is critical, with implications not only for the index patient but also potentially for family members, including the need for genetic counseling and sometimes particular types of surveillance. Together, contemporary sarcoma evaluation involves combining the initial morphologic evaluation with diagnostically relevant cytogenetic, molecular, and immunohistochemical testing methods.

Epigenetic Control of Schwann Cells

The journey of Schwann cells from their origin in the neural crest to their ensheathment and myelination of peripheral nerves is a remarkable one. Their apparent static function in enabling saltatory conduction of mature nerve is not only vital for long-term health of peripheral nerve but also belies an innate capacity of terminally differentiated Schwann cells to radically alter their differentiation status in the face of nerve injury. The transition from migrating neural crest cells to nerve ensheathment, and then myelination of large diameter axons has been characterized extensively and several of the transcriptional networks have been identified. However, transcription factors must also modify chromatin structure during Schwann cell maturation and this review will focus on chromatin modification machinery that is involved in promoting the transition to, and maintenance of, myelinating Schwann cells. In addition, Schwann cells are known to play important regenerative roles after peripheral nerve injury, and information on epigenomic reprogramming of the Schwann cell genome has emerged. Characterization of epigenomic requirements for myelin maintenance and Schwann cell responses to injury will be vital in understanding how the various Schwann cell functions can be optimized to maintain and repair peripheral nerve function.

Distinct histone modifications denote early stress-induced drug tolerance in cancer

Besides somatic mutations or drug efflux, epigenetic reprogramming can lead to acquired drug resistance. We recently have identified early stress-induced multi-drug tolerant cancer cells termed induced drug-tolerant cells (IDTCs). Here, IDTCs were generated using different types of cancer cell lines; melanoma, lung, breast and colon cancer. A common loss of the H3K4me3 and H3K27me3 and gain of H3K9me3 mark was observed as a significant response to drug exposure or nutrient starvation in IDTCs. These epigenetic changes were reversible upon drug holidays. Microarray, qRT-PCR and protein expression data confirmed the up-regulation of histone methyltransferases (SETDB1 and SETDB2) which contribute to the accumulation of H3K9me3 concomitantly in the different cancer types. Genome-wide studies suggest that transcriptional repression of genes is due to concordant loss of H3K4me3 and regional increment of H3K9me3. Conversely, genome-wide CpG site-specific DNA methylation showed no common changes at the IDTC state. This suggests that distinct histone methylation patterns rather than DNA methylation are driving the transition from parental to IDTCs. In addition, silencing of SETDB1/2 reversed multi drug tolerance. Alterations of histone marks in early multi-drug tolerance with an increment in H3K9me3 and loss of H3K4me3/H3K27me3 is neither exclusive for any particular stress response nor cancer type specific but rather a generic response.

Significance of H3K27me3 loss in the diagnosis of malignant peripheral nerve sheath tumors

The diagnosis of malignant peripheral nerve sheath tumors can be challenging and other spindle cell sarcomas commonly enter in the differential diagnosis. Loss of trimethylation at lysine 27 of histone-H3 (H3K27me3) by immunohistochemistry was recently described in malignant peripheral nerve sheath tumors. However, its specificity remains controversial. We therefore studied 82 synovial sarcomas, 39 malignant peripheral nerve sheath tumors, and 10 fibrosarcomatous dermatofibrosarcoma protuberans for H3K27me3 loss by immunohistochemistry. The diagnoses were based on morphology, immunophenotype, and genetics based on WHO classification. H3K27me3 immunohistochemistry was scored by two pathologists based on fraction of cells with nuclear staining (score 0 to 3+). Loss of H3K27me3 (score 0) was seen in 44% of malignant peripheral nerve sheath tumors and 9% of synovial sarcomas yielding positive and negative predictive values of 71% and 77%, respectively. Loss of H3K27me3 was seen in 10% of fibrosarcomatous dermatofibrosarcoma protuberans, yielding positive and negative predictive values of 94 and 29% in the differential diagnosis of malignant peripheral nerve sheath tumor versus fibrosarcomatous dermatofibrosarcoma protuberans. Partial loss (score 1-2) was common in all three tumor types. Among malignant peripheral nerve sheath tumors, there was no significant association between H3K27me3 loss and gender, tumor site, or size, and progression-free or overall survival. Patients with tumors with H3K27me3 loss were younger than those with tumors with retained H3K27me3 expression (P=0.011). H3K27me3 expression was lost in 50 and 31% of sporadic and Neurofibromatosis-associated malignant peripheral nerve sheath tumors, respectively (P=0.25).Complete H3K27me3 loss is a moderately sensitive and relatively specific marker for the diagnosis of malignant peripheral nerve sheath tumor when the differential diagnosis includes synovial sarcoma and fibrosarcomatous dermatofibrosarcoma protuberans. Partial loss has limited diagnostic utility. H3K27me3 status does not show significant association with clinical outcome in malignant peripheral nerve sheath tumors.

Epigenetic Alterations in Bone and Soft Tissue Tumors

Human malignancies are driven by heritable alterations that lead to unchecked cellular proliferation, invasive growth and distant spread. Heritable changes can arise from changes in DNA sequence, or, alternatively, through altered gene expression rooted in epigenetic mechanisms. In recent years, high-throughput sequencing of tumor genomes has revealed a central role for mutations in epigenetic regulatory complexes in oncogenic processes. Through interactions with or direct modifications of chromatin, these proteins help control the accessibility of genes, and thus the transcriptional profile of a cell. Dysfunction in these proteins can lead to activation of oncogenic pathways or silencing of tumor suppressors. Although epigenetic regulators are altered across a broad spectrum of human malignancies, they play a particularly central role in tumors of mesenchymal and neuroectodermal origin. This review will focus on recent advances in the understanding of the molecular pathogenesis of a subset of tumors in which alterations in the polycomb family of chromatin modifying complexes, the SWI/SNF family of nucleosome remodelers, and histones play a central role in disease pathogenesis. Although this review will focus predominantly on the molecular mechanisms underlying these tumors, each section will also highlight areas in which an understanding of the molecular pathogenesis of these diseases has led to the adoption of novel immunohistochemical and molecular markers.

Recent advances in the diagnosis of soft tissue tumours

Soft tissue tumours are relatively rare, but are diagnostically challenging as they comprise a large spectrum of diagnostic entities. Substantial advances have been made in recent years in identifying the underlying recurrent chromosomal and genomic alterations in a significant subset of soft tissue tumours, and this continues to enrich our understanding of the biological mechanisms of tumour development and progression. Ongoing validation and integration of these findings into existing pathological-diagnostic algorithms has led to re- or subclassification of diagnostic categories and will continue to shape a more nuanced (and hopefully clinically relevant) tumour classification system in the future. This review provides a selective overview of recent diagnostic or conceptual advances in the categories of peripheral nerve sheath tumours, vascular and adipocytic tumours, round cell and myogenic sarcomas, and gastrointestinal stromal tumours, as well as their underlying molecular mechanisms, some of which have been translated successfully into useful immunohistochemical stains. A thorough and critical validation of newly identified diagnostic markers-acknowledging the fact that some genetic alterations may not necessarily be tumour-specific-and ongoing correlation with clinical and prognostic implications will be necessary in this regard.

Successful treatment with doxorubicin and ifosfamide for mediastinal malignant peripheral nerve sheath tumor with loss of H3K27me3 expression

Malignant peripheral nerve sheath tumor (MPNST) in the thorax is an extremely rare disease, and half of all cases of MPNST are associated with neurofibromatosis type I. Sporadic intrathoracic MPNST is difficult to diagnose and treat. Because of the rarity of intrathoracic MPNST, the optimal method of diagnosis and the efficacy of chemotherapy are unknown. Herein, we present a case of inoperable mediastinal MPNST, in which the diagnosis was immunohistochemically made by the loss of H3K27me3 expression in a transbronchial needle biopsy specimen. The patient showed a good response to doxorubicin plus ifosfamide chemotherapy. The present case highlights that MPNST should be included in the differential diagnosis of non‐posterior mediastinum thoracic lesions, and that appropriate diagnosis and treatment for intrathoracic MPNST should be considered in patients with a thoracic mass.

Synovial Sarcoma of Peripheral Nerves: Analysis of 15 Cases

Synovial sarcoma of peripheral nerve (SSPN) is rare with only 26 cases reported in English. SSPN is often mistaken for a benign or malignant peripheral nerve sheath tumor (PNST) by clinicians and pathologists. Fifteen cases of SSPN were retrieved from the pathology files of 3 institutions. All tumors arose in a nerve based on imaging and/or operative findings and the diagnoses were histologically confirmed. Neuropathic symptoms predominated in 11 women and 4 men, 19- to 62-year-old (median, 39 years) with tumors involving the ulnar (5), median (3), peroneal (3) or sciatic (2) nerve, or the L4 or T1 nerve root (2). Tumor sizes ranged from 2 to 13 cm (median, 3.8 cm). The leading clinical diagnosis was PNST (9). Treatment was surgical (14) supplemented with radiation therapy (8) and chemotherapy (6). Fourteen tumors were monophasic and 1 was biphasic; 4 had poorly differentiated (PD) foci (1 rhabdoid). Diagnoses in 12 cases were verified by fluorescence in situ hybridization, reverse transcription polymerase chain reaction or both methods. Follow-up in 14 patients (median, 32 mo) revealed that 2/4 patients with PD tumors died with pulmonary metastases; another was alive with no current evidence of disease (NED) following 2 local recurrences, while the fourth had NED. In contrast, 9/10 patients without PD tumors were alive (7 NED) and 1 died at 12 months with pulmonary infiltrates. SSPN is under-recognized clinically and histologically as it mimics benign and malignant PNST. Molecular analysis is recommended to confirm the diagnosis. PD foci, including rhabdoid areas, may portend a worse outcome, similar to non-neural-based tumors.

[Tumors of the inner ear and adjacent structures]

Tumors of the inner ear and adjacent structures often present with hearing loss, tinnitus and vertigo due to compression of the traversing cranial nerves. More than 90% of the tumors of the inner ear with or without expansion into the cerebellopontine angle are histologically diagnosed as vestibular schwannomas. Less common tumorous lesions include ectopic meningiomas located in the petrous bone, glomus tympanicum paragangliomas or endolymphatic sac tumors (ELST) originating in the vestibular recess. Most tumors are sporadic, but hereditary disorders have to be considered. Bilateral vestibular schwannomas are indicative of neurofibromatosis type 2 and ELST in conjunction with other abdominal tumors indicates von Hippel-Lindau disease. The neuropathological diagnostics and grading guides the subsequent therapy of these mostly benign lesions.

The promise of signal transduction in genetically driven sarcomas of the nerve

Neurofibromatosis type 1 (NF1) is an autosomal dominant tumor predisposition syndrome. Malignant peripheral nerve sheath tumors (MPNST) are aggressive soft tissue sarcomas arising from peripheral nerve sheaths, and the most commonly lethal feature associated with NF1. The hallmark of NF1 and NF1-related MPNST is the loss of neurofibromin expression. Loss of neurofibromin is considered a tumor-promoting event, and leads to constitutive activation of RAS and its downstream effectors. However, RAS activation alone is not sufficient for MPNST formation, and additional tumor suppressors and signaling pathways have been implicated in tumorigenesis of MPNST. Taking advantage of the rapid development of novel therapeutics targeting key molecular pathways across all cancer types, the best-in-class modulators of these pathways can be assessed in pre-clinical models and translated into clinical trials for patients with MPNST. Here, we describe the genetic changes and molecular pathways that drive MPNST formation and highlight the promise of signal transduction to identify therapies that may treat these tumors more effectively.

NF1+/- Hematopoietic Cells Accelerate Malignant Peripheral Nerve Sheath Tumor Development without Altering Chemotherapy Response

Haploinsufficiency in the tumor suppressor NF1 contributes to the pathobiology of neurofibromatosis type 1, but a related role has not been established in malignant peripheral nerve sheath tumors (MPNST) where NF1 mutations also occur. Patients with NF1-associated MPNST appear to have worse outcomes than patients with sporadic MPNST, but the mechanism underlying this correlation is not understood. To define the impact of stromal genetics on the biology of this malignancy, we developed unique mouse models that reflect the genetics of patient-associated MPNST. Specifically, we used adenovirus-Cre injections to generate MPNST in Nf1Flox/Flox; Ink4a/ArfFlox/Flox and Nf1Flox/-; Ink4a/ArfFlox/Flox paired littermate mice to model tumors from NF1-wild-type and NF1-associated patients, respectively. In these models, Nf1 haploinsufficiency in hematopoietic cells accelerated tumor onset and increased levels of tumor-infiltrating immune cells comprised of CD11b+ cells, monocytes, and mast cells. We observed that mast cells were also enriched in human NF1-associated MPNST. In a coclinical trial to examine how the tumor microenvironment influences the response to multiagent chemotherapy, we found that stromal Nf1 status had no effect. Taken together, our results clarify the role of the NF1-haploinsufficient tumor microenvironment in MPNST. Cancer Res; 77(16); 4486-97. ©2017 AACR.

Role of Histone H3K27 Trimethylation Loss as a Marker for Malignant Peripheral Nerve Sheath Tumor in Fine-Needle Aspiration and Small Biopsy Specimens

OBJECTIVES

Accurate diagnosis of malignant peripheral nerve sheath tumor (MPNST) is often challenging on fine-needle aspiration (FNA) or core needle biopsy. Recurrent mutations in EED and SUZ12, which encode subunits of polycomb repressive complex 2 (PRC2), have been identified in 70% to 92% of MPNSTs; PRC2 inactivation leads to loss of trimethylation of lysine 27 of histone H3 (H3K27me3). We evaluated the utility of H3K27me3 immunohistochemistry for distinguishing MPNST from its cytomorphologic mimics.

METHODS

H3K27me3 immunohistochemistry was performed on 180 cases of spindle cell neoplasms sampled by FNA (n = 66) and needle biopsy (n = 114), and loss of nuclear staining was scored. Tumor types included MPNST, dedifferentiated liposarcoma, schwannoma, solitary fibrous tumor, leiomyosarcoma, melanoma, synovial sarcoma, sarcomatoid carcinoma, gastrointestinal stromal tumor, desmoid fibromatosis, low-grade fibromyxoid sarcoma, and unclassified spindle cell sarcoma/undifferentiated pleomorphic sarcoma.

RESULTS

Complete loss of H3K27me3 was observed in 54% (13/24) of MPNSTs. In contrast, only two (of 156) histologic mimics showed complete loss of H3K27me3. Partial loss of H3K27me3 was present in a subset of cases (26/180), including both MPNST and non-MPNSTs.

CONCLUSIONS

Complete loss of H3K27me3 is a highly specific (98.7%) marker of MPNST that can distinguish MPNST from cytomorphologic mimics in FNA cell block and small biopsy specimens.

A Clinicopathologic Study of Head and Neck Malignant Peripheral Nerve Sheath Tumors

Head and neck high grade malignant peripheral nerve sheath tumors (HN-MPNSTs) are rare highly aggressive soft tissue sarcomas that show overlapping morphologic and immunophenotypic features with melanoma and other high grade sarcomas, resulting in diagnostic challenges, particularly in sporadic settings. Recent discoveries have implicated loss of function mutations in the polycomb repressive complex 2 (PRC2) components, including EED or SUZ12 genes, as one of the leading pathogenetic mechanisms in high grade MPNST. MPNSTs with PRC2 loss are associated with complete loss of trimethylation at lysine 27 of histone H3 (H3K27me3), which emerged as a reliable immunohistochemical marker in the diagnosis of sporadic and radiation induced MPNST. As the diagnosis of MPNST in the HN is particularly challenging to distinguish from melanoma and other sarcoma types, we carried out a clinicopathologic analysis on HN-MPNST patients managed at our institution over a 20-year period (1997-2016), using the latest diagnostic criteria including H3K27me3 staining and other molecular investigations. The overall survival of HN-MPNST was compared with other HN soft tissue sarcomas. The diagnosis of HN-MPNST was confirmed in 13 patients (seven males and six females), with a mean age of 31 years; with 3 (23%) patients being of pediatric age. The most common site was the neck soft tissue (77%). Two-thirds of patients (n = 9) had stigmata of NF1, three had prior radiotherapy and only one developed a de novo MPNST. All except one tumor (86%) tested showed loss of H3K27me3 expression, including all non-NF1 patients. The 2 and 5-year DSS rates were 50 and 30%. The 2-year DFS rate was 21%. Adverse predictors on DSS included adult age (p = 0.011), prior-history of RT (p = 0.003) and recurrence (p = 0.003). Compared to other molecularly confirmed subsets of HN sarcomas (Ewing and Ewing-like sarcoma, rhabdomyosarcoma and synovial sarcoma), HN-MPNST had the worst overall survival (p < 0.0001). We conclude that HN-MPNSTs are highly aggressive sarcomas associated with an unfavorable outcome and the utility of H3K27me3 IHC stains in the evaluation of MPNST is a reliable ancillary diagnostic adjunct.

Polycomb Repressor Complex 2 in Genomic Instability and Cancer

Polycomb repressor complexes PRC1 and PRC2 regulate chromatin compaction and gene expression, and are widely recognized for their fundamental contributions to developmental processes. Herein, we summarize the existing evidence and molecular mechanisms linking PRC-mediated epigenetic aberrations to genomic instability and malignancy, with a particular focus on the role of deregulated PRC2 in tumor suppressor gene expression, the DNA damage response, and the fidelity of DNA replication. We also discuss some of the recent advances in the development of pharmacological and dietary interventions affecting PRC2, which point to promising applications for the prevention and management of human malignancies.

Reduced H3K27me3 Expression Is Common in Nodular Melanomas of Childhood Associated With Congenital Melanocytic Nevi But Not in Proliferative Nodules

The formation of a nodule within a congenital melanocytic nevus (CMN) raises concerns about possible melanoma. Most new nodular growths that develop during childhood, however, are benign proliferative nodules (PN); melanoma is very rare. The distinction of melanoma from PN can at times be difficult clinically and histopathologically, requiring ancillary molecular tests for diagnosis. Although the application of molecular methods has revealed new insights into the mutational and genomic landscape of childhood melanomas, little is known about epigenetic events that may drive the growth of a melanoma or PN in a CMN. In this study we compared the expression of H3K27me3, a key regulator in chromatin remodelling-controlled transcription, in PNs and pediatric nodular melanomas arising within medium-sized to large CMN by immunohistochemistry. Significant loss of H3K27me3 expression was seen in 4 of 5 melanomas, but not in any of the 20 PNs. This observation suggests that epigenetic events likely play a role in the pathogenesis of melanoma developing in the dermis or subcutis of CMN. Furthermore, assessing for H3K27me3 expression by immunohistochemistry may be diagnostically useful for problematic cases.

Desmoplastic melanoma may mimic a cutaneous peripheral nerve sheath tumor: Report of 3 challenging cases

Desmoplastic melanoma (DM) and cutaneous malignant peripheral nerve sheath tumors (MPNST) reveal histological and immunohistochemical similarities, including S100 positivity and negative staining for conventional melanocytic markers. We present 3 cases of cutaneous S100‐positive spindle cell tumors in elderly patients, in which first findings led to initial misdiagnoses as cutaneous MPNST and benign peripheral sheath nerve tumor (neurofibroma). The identification of adjacent atypical melanocytic hyperplasia in the overlying skin along with tumor cell proliferation, also in the superficial dermis, the neurotropic component and the absence of any relationship between the tumor and a major nerve, pre‐existing neural benign tumor or the existence of stigmata suggestive of neurofibromatosis raised consideration of a DM. Careful attention should be paid to the presence of a firm dermal nodule and atypical scar lesions especially in sun‐exposed areas (mainly head and neck region) in elderly patients associated with S100‐positive spindle cell proliferation, solar elastosis and adjacent atypical melanocytic proliferation. In such cases, the possibility of a DM should be excluded with caution, especially if the tumor reveals a paucicellular morphology resembling various non‐melanocytic neoplasms including malignant or benign peripheral sheath nerve tumors.

Molecular profiling of sarcomas: new vistas for precision medicine

Sarcoma is a large and heterogeneous group of malignant mesenchymal neoplasms with significant histological overlap. Accurate diagnosis can be challenging yet important for selecting the appropriate treatment approach and prognosis. The currently torrid pace of new genomic discoveries aids our classification and diagnosis of sarcomas, understanding of pathogenesis, development of new medications, and identification of alterations that predict prognosis and response to therapy. Unfortunately, demonstrating effective targets for precision oncology has been elusive in most sarcoma types. The list of potential targets greatly outnumbers the list of available inhibitors at the present time. This review will discuss the role of molecular profiling in sarcomas in general with emphasis on selected entities with particular clinical relevance.

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.

Malignant Peripheral Nerve Sheath Tumor of the Femur: A Rare Diagnosis Supported by Complete Immunohistochemical Loss of H3K27me3

The histological diagnosis of malignant peripheral nerve sheath tumor (MPNST) is challenging because of the wide morphological spectrum and suboptimal performance of conventional immunohistochemical markers. MPNST arising primarily in the bone is exceptional, and its definitive diagnosis, particularly out of the neurofibromatosis type 1 (NF1) context, is even more problematic. Recurrent inactivation of EED or SUZ12 in a majority of MPNSTs results in a complete loss of trimethylated histone H3 at lysine 27 (H3K27me3) immunoreactivity, making it a highly specific biomarker of MPNSTs. In this article, we report a case of sporadic MPNST of the proximal femur that showed complete loss of H3K27me3. The patient was treated with limb-sparing surgery and postoperative radiotherapy. He developed multiple lung and bone metastases 4 months after surgery. Our case confirms the utility of H3K27me3 immunohistochemistry to yield a definitive diagnosis of sporadic MPNST in a rare primary site.

Malignant Peripheral Nerve Sheath Tumors State of the Science: Leveraging Clinical and Biological Insights into Effective Therapies

Malignant peripheral nerve sheath tumor (MPNST) is the leading cause of mortality in patients with neurofibromatosis type 1. In 2002, an MPNST consensus statement reviewed the current knowledge and provided guidance for the diagnosis and management of MPNST. Although the improvement in clinical outcome has not changed, substantial progress has been made in understanding the natural history and biology of MPNST through imaging and genomic advances since 2002. Genetically engineered mouse models that develop MPNST spontaneously have greatly facilitated preclinical evaluation of novel drugs for translation into clinical trials led by consortia efforts. Continued work in identifying alterations that contribute to the transformation, progression, and metastasis of MPNST coupled with longitudinal follow-up, biobanking, and data sharing is needed to develop prognostic biomarkers and effective prevention and therapeutic strategies for MPNST.

Malignant Peripheral Nerve Sheath Tumor With Divergent Glandular Differentiation

Malignant peripheral nerve sheath tumors (MPNST) are soft tissue neoplasms with evidence of nerve sheath differentiation. They usually arise from peripheral nerves or from preexisting benign nerve sheath neoplasms, often in patients with neurofibromatosis type 1 (NF1). The histologic diagnosis of MPNST is challenging as their morphology is highly variable, and there has been a lack of routine diagnostic immunohistochemical markers and specific genetic aberrations. Although divergent differentiation is well documented in MPNST, it is most frequently toward mesenchymal elements. Differentiation toward epithelial elements is very rare, and we illustrate a case of MPNST with glandular differentiation, comprising prominent well-formed glands, with a brief discussion of biphasic (spindle and glandular) neoplasms in the differential diagnosis. An index of suspicion for MPNST is necessary, due to the differing management from tumors in its differential diagnosis, and because of the potential for therapies toward molecular targets in future.

Emerging genotype-phenotype relationships in patients with large NF1 deletions

The most frequent recurring mutations in neurofibromatosis type 1 (NF1) are large deletions encompassing the NF1 gene and its flanking regions (NF1 microdeletions). The majority of these deletions encompass 1.4-Mb and are associated with the loss of 14 protein-coding genes and four microRNA genes. Patients with germline type-1 NF1 microdeletions frequently exhibit dysmorphic facial features, overgrowth/tall-for-age stature, significant delay in cognitive development, large hands and feet, hyperflexibility of joints and muscular hypotonia. Such patients also display significantly more cardiovascular anomalies as compared with patients without large deletions and often exhibit increased numbers of subcutaneous, plexiform and spinal neurofibromas as compared with the general NF1 population. Further, an extremely high burden of internal neurofibromas, characterised by >3000 ml tumour volume, is encountered significantly, more frequently, in non-mosaic NF1 microdeletion patients than in NF1 patients lacking such deletions. NF1 microdeletion patients also have an increased risk of malignant peripheral nerve sheath tumours (MPNSTs); their lifetime MPNST risk is 16-26%, rather higher than that of NF1 patients with intragenic NF1 mutations (8-13%). NF1 microdeletion patients, therefore, represent a high-risk group for the development of MPNSTs, tumours which are very aggressive and difficult to treat. Co-deletion of the SUZ12 gene in addition to NF1 further increases the MPNST risk in NF1 microdeletion patients. Here, we summarise current knowledge about genotype-phenotype relationships in NF1 microdeletion patients and discuss the potential role of the genes located within the NF1 microdeletion interval whose haploinsufficiency may contribute to the more severe clinical phenotype.

Radiation-associated neoplasia: clinical, pathological and genomic correlates

Ionizing radiation is an established risk factor for the development of benign and malignant tumours. The epidemiology of radiation-associated neoplasia has been studied over the decades in diverse populations, including Japanese atomic bomb survivors, exposed communities following the Chernobyl nuclear power plant disaster, and paediatric and adult populations receiving therapeutic irradiation. Radiation has been associated with an increased risk of neoplasia throughout the human body, with some sites showing a markedly increased relative risk of developing tumours (thyroid; soft tissues), depending on patient age and the context of exposure. Although the mechanisms of cellular injury and repair resulting from ionizing radiation are well described, the genomics of radiation-induced tumours are still relatively poorly understood, with some exceptions, such as RET rearrangement in thyroid carcinomas following iodine-131 exposure and MYC amplification in cutaneous angiosarcoma following chest wall irradiation for breast cancer. This review will provide a general overview of the epidemiology, molecular mechanism, pathology and genomics of radiation-associated neoplasia in humans.

The role of phosphorylated signal transducer and activator of transcription 3 (pSTAT3) in peripheral nerve sheath tumours

AIMS

STAT3 is a pro-oncogenic transcription factor that requires phosphorylation for transcriptional activation. The aim of this study was to evaluate the role of phosphorylated STAT3 (pSTAT3) expression in neurofibromas, schwannomas, and malignant peripheral nerve sheath tumours (MPNSTs).

METHODS AND RESULTS

Twenty-six neurofibromas, 62 schwannomas and 39 MPNSTs from a formalin-fixed paraffin-embedded tissue microarray were examined. Immunohistochemical analysis was performed with an anti-pSTAT3 (Tyr705) antibody. Nuclear expression was reviewed for both intensity and percentage of tumoral labelling. Distributions of disease-specific overall survival (DSOS) and event-free survival (EFS) were estimated with the Kaplan-Meier method, and compared between two pSTAT3 groups by use of the log-rank test. MPNSTs had higher median tumoral labelling than neurofibromas (P = 0.0012) or schwannomas (P = 0.0008). Moderate to strong pSTAT3 expression (defined as at least moderate labelling in ≥50% of cells) was found more frequently in MPNSTs than in neurofibromas (P = 0.026). Among MPNSTs, pSTAT3 expression differed between primary, recurrent and metastatic disease (P = 0.063 with increased expression in recurrent and metastatic cases). pSTAT3 expression (at least moderate labelling in ≥10% of cells) in primary MPNSTs was associated with worse DSOS (P = 0.048) and trended towards being associated with worse EFS (P = 0.063). Paired specimens revealed no increase in pSTAT3 expression in the recurrences or metastases relative to the primary tumour, suggesting that pSTAT3 expression may be an early indicator of aggressive disease at disease onset.

CONCLUSIONS

pSTAT3 is expressed in a higher proportion of MPNSTs than neurofibromas and schwannomas. Moderate to strong pSTAT3 expression in ≥10% of cells was found to be a negative prognostic factor for DSOS among primary MPNSTs, suggesting a role of pSTAT3 in the progression of these tumours.

Immunohistochemistry for trimethylated H3K27 in the diagnosis of malignant peripheral nerve sheath tumours

AIMS

The diagnosis of a malignant peripheral nerve sheath tumour (MPNST) can be challenging, as the morphological criteria and existing immunohistochemical markers are not entirely specific. The recent discovery of frequent inactivation of polycomb repressive complex 2 in MPNSTs suggests that immunohistochemical detection of histone 3 trimethylated on lysine 27 (H3K27me3) could be of diagnostic help. This study aimed to clarify the utility of this marker.

METHODS AND RESULTS

We performed immunostaining studies, with monoclonal (C36B11) and polyclonal antibodies in parallel. With the monoclonal antibody, 56% of 54 conventional MPNSTs showed complete loss of staining, whereas 17% showed mosaic loss and 28% showed intact staining. Three MPNSTs showed a novel geographical pattern of complete loss. All three epithelioid MPNSTs retained intact staining. Among 232 non-MPNSTs, only two (0.9%) showed complete loss of staining. Mosaic loss was observed in 38% of non-MPNSTs, whereas the remaining 61% retained intact staining. For conventional MPNSTs, complete loss of H3K27me3 was significantly associated with a higher TNM stage (P = 0.013), a deeper location (P = 0.004), and the presence of heterologous differentiation (P = 0.003). Polyclonal antibodies did not recognize 34% of cases that showed complete loss with the use of monoclonal antibodies.

CONCLUSIONS

We confirmed that complete loss of H3K27me3 immunohistochemical staining is moderately sensitive and highly specific for MPNSTs. In contrast to prior studies, we found that mosaic loss of H3K27me3 staining is non-specific, and caution that such a pattern should not be considered to be diagnostic. We recommend the use of a monoclonal antibody to obtain better performance.

Low-grade Schwann cell neoplasms with leptomeningeal dissemination: clinicopathologic and autopsy findings

Leptomeningeal dissemination of low-grade Schwann cell neoplasms is an exceptionally rare occurrence and has not been well documented in the literature. We encountered 2 cases of leptomeningeal dissemination of low-grade Schwann cell neoplasms. Patient 1 was a 63-year-old woman with neurofibromatosis type 1 and a progressive low-grade malignant peripheral nerve sheath tumor developing from a diffuse/plexiform orbital neurofibroma that arose in childhood. The neoplasm demonstrated local and leptomeningeal dissemination intracranially leading to the patient's death. There was partial loss of H3K27 tri-methylation, p16 and collagen IV. Patient 2 was a 60-year-old man without neurofibromatosis type 1 who presented with cranial nerve symptoms and a disseminated neoplasm with a Schwann cell phenotype. The neoplasm stabilized after irradiation and chemotherapy, but the patient died of medical complications. Autopsy findings documented disseminated leptomeningeal disease in the intracranial and spinal compartment. H3K27M tri-methylation was preserved. The clinicopathologic and autopsy findings are studied and presented, and the literature is reviewed.

Association between EZH2 expression, silencing of tumor suppressors and disease outcome in solid tumors

EZH2, the main catalytic component of the Polycomb Repressive Complex 2 (PRC2) is apparently upregulated in most solid tumors. Furthermore its expression generally associates with poor prognosis. It was proposed that this correlation reflects a causal event, EZH2 mediating the silencing of key tumor suppressor loci. In contrast, we recently showed that EZH2 is dispensable for solid tumor development and that its elevated expression reflects the abnormally high proliferation rate of cancer cells. Here, we investigate the functional association between EZH2 expression and silencing of key tumor suppressor loci and further illustrate the confounding effect of proliferation on EZH2′s association to outcome.