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

Consensus recommendations for an integrated diagnostic approach to peripheral nerve sheath tumors arising in the setting of Neurofibromatosis Type 1

Consensus recommendations 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 and 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 noncutaneous 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.

Polycomb repressive complex 2 (PRC2) pathway's role in cancer cell plasticity and drug resistance

Polycomb Repressive Complex 2 (PRC2) is a central regulator of gene expression via the trimethylation of histone H3 on lysine 27. This epigenetic modification plays a crucial role in maintaining cell identity and controlling differentiation, while its dysregulation is closely linked to cancer progression. PRC2 silences tumor suppressor genes, promoting cell proliferation, metastasis, epithelial-mesenchymal transition, and cancer stem cell plasticity. Enhancement of zeste homolog 2 (EZH2) overexpression or gain-of-function mutations have been observed in several cancers, including lymphoma, breast, and prostate cancers, driving aggressive tumor behavior and drug resistance. In addition to EZH2, other PRC2 components, such as embryonic ectoderm development (EED) and suppressor of zeste 12, are essential for complex stability and function. EED, in particular, enhances EZH2 activity and has emerged as a therapeutic target. Inhibitors like MAK683 and EED226 disrupt EED's ability to maintain PRC2 activity, thereby reducing H3K27me3 levels and reactivating tumor suppressor genes. Valemetostat, a dual inhibitor of both EZH2 and EED, has shown promising results in aggressive cancers like diffuse large B-cell lymphoma and small-cell lung cancer, underlining the therapeutic potential of targeting multiple PRC2 components. PRC2's role extends beyond gene repression, as it contributes to metabolic reprogramming in tumors, regulating glycolysis and lipid synthesis to fuel cancer growth. Furthermore, PRC2 is implicated in chemoresistance, particularly by modulating DNA damage response and immune evasion. Tazemetostat, a selective EZH2 inhibitor, has demonstrated significant clinical efficacy in EZH2-mutant cancers, such as non-Hodgkin lymphomas and epithelioid sarcoma. However, the compensatory function of enhancer of zeste homolog 1 (EZH1) in some cancers requires dual inhibition strategies, as seen with agents like UNC1999 and Tulmimetostat, which target both EZH1 and EZH2. Given PRC2's multifaceted role in cancer biology, its inhibition represents a promising avenue for therapeutic intervention. The continued development of PRC2 inhibitors and exploration of their use in combination with standard chemotherapy or immunotherapy has great potential for improving patient outcomes in cancers driven by PRC2 dysregulation.

Spatial Lipidomics Reveals Myelin Defects and Protumor Macrophage Infiltration in Malignant Peripheral Nerve Sheath Tumor Adjacent Nerves

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive sarcomas arising from peripheral nerves, accounting for 3% to 5% of soft tissue sarcomas. MPNSTs often recur locally, leading to poor survival. Achieving tumor-free surgical margins is essential to prevent recurrence, but current methods for determining tumor margins are limited, highlighting the need for improved biomarkers. In this study we investigated the degree to which MPNST extends into nerves adjacent to tumors. Alterations to the lipidome of MPNST and adjacent peripheral nerves were assessed using spatial lipidomics. Tissue samples from 5 patients with MPNST were analyzed, revealing alterations of the lipid profile extending into the peripheral nerves beyond what was expected based on macroscopic and histologic observations. Integration of spatial lipidomics and high-resolution accurate-mass profiling identified distinct lipid profiles associated with healthy nerves, connective tissue, and tumors. Notably, histologically normal nerves exhibited myelin degradation and infiltration of protumoral M2 macrophages, particularly near the tumor. Furthermore, aberrant osmium staining patterns and loss of H3K27me3 staining in the absence of atypia were observed in a case with tumor recurrence. This exploratory study thereby highlights the changes occurring in the nerves affected by MPNST beyond what is visible on hematoxylin and eosin staining and provides leads for further biomarker studies, including aberrant osmium staining, to assess resection margins in MPNST.

Refractory testicular germ cell tumors are highly sensitive to the targeting of polycomb pathway demethylases KDM6A and KDM6B

Testicular germ cell tumors (TGCTs) can be treated with cisplatin-based therapy. However, a clinically significant number of cisplatin-resistant patients die from progressive disease as no effective alternatives exist. Curative cisplatin therapy results in acute and life-long toxicities in the young TGCT patient population providing a rationale to decrease cisplatin exposure. In contrast to genetic alterations, recent evidence suggests that epigenetics is a major driving factor for TGCT formation, progression, and response to chemotherapy. Hence, targeting epigenetic pathways with "epidrugs" is one potential relatively unexplored strategy to advance TGCT treatment beyond cisplatin. In this report, we demonstrate for the first time that targeting polycomb demethylases KDM6A and KDM6B with epidrug GSK-J4 can treat both cisplatin-sensitive and -resistant TGCTs. While GSK-J4 had minimal effects alone on TGCT tumor growth in vivo, it dramatically sensitized cisplatin-sensitive and -resistant TGCTs to cisplatin. We validated KDM6A/KDM6B as the target of GSK-J4 since KDM6A/KDM6B genetic depletion had a similar effect to GSK-J4 on cisplatin-mediated anti-tumor activity and transcriptome alterations. Pharmacologic and genetic targeting of KDM6A/KDM6B potentiated or primed the p53-dominant transcriptional response to cisplatin, with also evidence for basal activation of p53. Further, several chromatin modifier genes, including BRD4, lysine demethylases, chromodomain helicase DNA binding proteins, and lysine methyltransferases, were repressed with cisplatin only in KDM6A/KDM6B-targeted cells, implying that KDM6A/KDM6B inhibition sets the stage for extensive chromatin remodeling of TGCT cells upon cisplatin treatment. Our findings demonstrate that targeting polycomb demethylases is a new potent pharmacologic strategy for treating cisplatin resistant TGCTs that warrants clinical development.

Refractory testicular germ cell tumors are highly sensitive to the targeting of polycomb pathway demethylases KDM6A and KDM6B

Testicular germ cell tumors (TGCTs) can be treated with cisplatin-based therapy. However, a clinically significant number of cisplatin-resistant patients die from progressive disease as no effective alternatives exist. Curative cisplatin therapy results in acute and life-long toxicities in the young TGCT patient population providing a rationale to decrease cisplatin exposure. In contrast to genetic alterations, recent evidence suggests that epigenetics is a major driving factor for TGCT formation, progression, and response to chemotherapy. Hence, targeting epigenetic pathways with "epidrugs" is one potential relatively unexplored strategy to advance TGCT treatment beyond cisplatin. In this report, we demonstrate for the first time that targeting polycomb demethylases KDM6A and KDM6B with epidrug GSK-J4 can treat both cisplatin-sensitive and -resistant TGCTs. While GSK-J4 had minimal effects alone on TGCT tumor growth in vivo, it dramatically sensitized cisplatin-sensitive and -resistant TGCTs to cisplatin. We validated KDM6A/KDM6B as the target of GSK-J4 since KDM6A/KDM6B genetic depletion had a similar effect to GSK-J4 on cisplatin-mediated anti-tumor activity and transcriptome alterations. Pharmacologic and genetic targeting of KDM6A/KDM6B potentiated or primed the p53-dominant transcriptional response to cisplatin, with also evidence for basal activation of p53. Further, several chromatin modifier genes, including BRD4, lysine demethylases, chromodomain helicase DNA binding proteins, and lysine methyltransferases, were repressed with cisplatin only in KDM6A/KDM6B-targeted cells, implying that KDM6A/KDM6B inhibition sets the stage for extensive chromatin remodeling of TGCT cells upon cisplatin treatment. Our findings demonstrate that targeting polycomb demethylases is a new potent pharmacologic strategy for treating cisplatin resistant TGCTs that warrants clinical development.

Contemporary Approach to Neurofibromatosis Type 1-Associated Malignant Peripheral Nerve Sheath Tumors

Most malignant peripheral nerve sheath tumors (MPNSTs) are clinically aggressive high-grade sarcomas, arising in individuals with neurofibromatosis type 1 (NF1) at a significantly elevated estimated lifetime frequency of 8%-13%. In the setting of NF1, MPNSTs arise from malignant transformation of benign plexiform neurofibroma and borderline atypical neurofibromas. Composed of neoplastic cells from the Schwannian lineage, these cancers recur in approximately 50% of individuals, and most patients die within five years of diagnosis, despite surgical resection, radiation, and chemotherapy. Treatment for metastatic disease is limited to cytotoxic chemotherapy and investigational clinical trials. In this article, we review the pathophysiology of this aggressive cancer and current approaches to surveillance and treatment.

An algorithmic approach to the management of peripheral nerve tumours

This article reviews the pathology and management of peripheral nerve tumours, including a framework for investigation and decision-making. Most tumours are benign, including schwannomas and neurofibromas, but malignant peripheral nerve sheath tumours can occur. The risk of malignant change is remote for schwannomas but higher for neurofibromas, particularly in neurofibromatosis type 1. Magnetic resonance imaging is useful for defining the relationship of a swelling with adjacent nerves but is not definitive for tissue diagnosis. Increasing size, pain and neurological deficit suggest malignant change and TruCut needle biopsy is indicated, although there is a risk of sampling error. Excision biopsy preserving nerve function may be carried out for benign tumours to relieve symptoms. Malignant tumours require a multidisciplinary approach. Complete surgical excision with clear margins is the only curative treatment and may be supplemented with radiotherapy and chemotherapy. However, prognosis remains poor, particularly for patients with neurofibromatosis.

Update on immunohistochemistry in bone and soft tissue tumors: Cost-effectively replacing molecular testing with immunohistochemistry

Soft tissue tumors form part of a challenging domain in diagnostic pathology owing to their comparative rarity, astonishing histologic diversity, and overlap between entities. Many of these tumors are now known to be defined by highly recurrent, or, in some instances, unique molecular alterations. Insights from gene profiling continue to elucidate the wider molecular landscape of soft tissue tumors; many of these advances have been co-opted by immunohistochemistry (IHC) for diagnostic applications. There now exists a multitude of antibodies serving as surrogate markers of recurrent gene fusions, amplifications, and point mutations, which, in certain settings, can replace the need for more resource and time-intensive cytogenetic and molecular genetic analyses. IHC presents many advantages including rapid turnaround time, cost-effectiveness, and interpretative reproducibility. A sensible application of these immunohistochemical markers complemented by a working knowledge of the molecular pathogenesis of bone and soft tissue tumors permits accurate diagnosis in the majority of cases. In this review, we will outline some of these biomarkers while emphasizing molecular correlates and highlighting interpretative challenges and pitfalls.

Peripheral nerve tumors

The chapter is focused on the neoplastic peripheral nerve lesions, which primarily involve "cranial and paraspinal nerves," as outlined in the CNS volume (WHO_Classification_of_Tumours_Editorial_Board, 2021). These include classic peripheral nerve sheath tumors such as schwannoma, neurofibroma, intraneural perineurioma, and malignant peripheral nerve sheath tumors, with their variants as well as new and more precisely defined entities, including hybrid nerve sheath tumors and malignant melanotic nerve sheath tumor (previously melanotic schwannoma).

Epigenetic determinants in soft tissue sarcomas: molecular mechanisms and therapeutic targets

INTRODUCTION

Soft tissue sarcomas are a group of rare, mesenchymal tumors characterized by dismal prognosis in advanced/metastatic stages. Knowledge of their molecular determinants is still rather limited. However, in recent years, epigenetic regulation - the modification of gene expression/function without DNA sequence variation - has emerged as a key player both in sarcomagenesis and sarcoma progression.

AREAS COVERED

Herein, we describe and review the main epigenetic mechanisms involved in chromatin remodeling and their role as disease drivers in different soft tissue sarcoma histotypes, focusing on epithelioid sarcoma, synovial sarcoma, and malignant peripheral nerve sheath tumors. Focusing on chromatin-remodeling complexes, we provide an in-depth on the role of BAF complex alterations in these soft tissue sarcoma histotypes. In parallel, we highlight current state-of-the-art and future perspectives in the development of rational, innovative treatments leveraging on epigenetic dysregulation in soft tissue sarcomas.

EXPERT OPINION

Therapeutic options for metastatic/advanced sarcomas are to date very limited and largely represented by cytotoxic agents, with only modest results. In the continuous attempt to find novel targets and innovative, effective drugs, epigenetic mechanisms represent an emerging and promising field of research, especially for malignant peripheral nerve sheath tumors, epithelioid and synovial sarcoma.

A distal ileum malignant peripheral nerve sheath tumour after abdominal radiation therapy: case report of a rare tumour

Malignant peripheral nerve sheath tumours (MPNSTs) are malignant tumours arising from a peripheral nerve or displaying nerve sheath differentiation. Most MPNSTs are found on the head, body trunk and extremities, whereas cases in the gastrointestinal are extremely rare. About half arise in neurofibromatosis type 1 patients and 10% arise post-irradiation. This is probably the first small bowel MPNST post-radiation therapy case reported. A 72-year-old female who received radiotherapy 30 years ago for cervical cancer was admitted with progressive abdominal pain and weight loss. Computed tomography revealed a mass with inhomogeneous enhancement in the lumen of the small intestine. Tumour excision was performed with ileocecal and sigmoid colon resection due to suspicion for peripheral tissue invasion. Histopathological examination revealed spindle-shaped cells with focal cartilage differentiation. Together with immunochemistry stain showing complete loss of H3K27me3, a final diagnosis of MPNST was made. The patient is presently under regular follow-ups, and has remained disease-free for 24 months.

Clinicopathological study of malignant peripheral nerve sheath tumors in the head and neck: Case reports and review of literature

BACKGROUND

Malignant peripheral nerve sheath tumor (MPNST) is a rare and aggressive soft tissue sarcoma that poses a major diagnostic and therapeutic challenge.

CASE SUMMARY

We retrospectively reviewed patients with head and neck MPNSTs treated in our hospital from 2000 to 2021. The clinical features, pathological manifestations, treatments, and prognoses were summarized. We also reviewed the literature, focusing on MPNST in the mandible and maxilla. The study population consisted of five women and five men aged 22-75 years (mean age, 49 years). Of the 10 patients, 7 were initial cases and 3 were recurrent cases. All lesions were sporadic. The most common site was the mandible. The most frequently encountered symptoms were a progressive mass and local swelling. Complete or partial loss of trimethylation at lysine 27 of histone H3 (H3K27me3) was evident on staining in four of nine cases (one case was excluded due to lack of tissue for evaluation of loss of H3K27me3). The 2- and 5-year disease-specific survival rates were 86% and 43%, respectively. The average survival time was 64 mo.

CONCLUSION

MPNST is a highly malignant tumor with a poor prognosis, prone to a high risk of recurrence and distant metastasis. Complete surgical resection is the main treatment.

Targeting epigenetic aberrations of sarcoma in CRISPR era

Sarcomas are rare malignancies that exhibit diverse biological, genetic, morphological, and clinical characteristics. Genetic alterations, such as gene fusions, mutations in transcriptional machinery components, histones, and DNA methylation regulatory molecules, play an essential role in sarcomagenesis. These mutations induce and/or cooperate with specific epigenetic aberrations required for the growth and maintenance of sarcomas. Appropriate mouse models have been developed to clarify the significance of genetic and epigenetic interactions in sarcomas. Studies using the mouse models for human sarcomas have demonstrated major advances in our understanding the developmental processes as well as tumor microenvironment of sarcomas. Recent technological progresses in epigenome editing will not only improve the studies using animal models but also provide a direct clue for epigenetic therapies. In this manuscript, we review important epigenetic aberrations in sarcomas and their representative mouse models, current methods of epigenetic editing using CRISPR/dCas9 systems, and potential applications in sarcoma studies and therapeutics.

NTRK-rearranged spindle cell neoplasms: a clinicopathological and molecular study of 13 cases with peculiar characteristics at one of the largest institutions in China

NTRK-rearranged spindle cell neoplasms (NTRK-RSCNs) represent an emerging group of rare tumours defined using molecular means. To the best of our knowledge, there have been no large series of reports about this tumour in the Chinese population in English full-text articles. Herein, we present 13 NTRK-RSCNs with peculiar characteristics. Ten of the 13 (77%) patients were children without sex differences. The tumour locations included six trunks, four extremities, two recta, and one small bowel. The histological morphology included four lipofibromatosis-like neural tumour (LPF-NT)-like, eight malignant peripheral nerve sheath tumours (MPNST)/fibrosarcoma-like, and one extremely rare myxofibrosarcoma-like pattern. Immunohistochemically, all cases were CD34, pan-TRK and TRK-A positive, SOX-10 negative, and H3K27me3 intact. S-100 protein expression was identified in 11 of 13 (85%) cases. Genetically, NTRK1 rearrangements were considered positive (7/13, 54%) or suspicious for positivity (6/13, 46%) by fluorescence in situ hybridisation. Next-generation sequencing and Sanger sequencing confirmed NTRK1 fusions with a variety of partner genes, including five LMNA, three TPM3, one SQSTM1, three novel CPSF6, IGR (downstream PMVK), and GAS2L1 genes. Interestingly, the last tumour concurrently harboured a second EWSR1-PBX1 fusion, which has never been reported. Four patients developed local recurrence and two of them suffered metastasis. In our study, NTRK-RSCNs had peculiar fusions that displayed unusual or complicated clinicopathological features. Histological clues and IHC helped streamline a small subset of potential candidates. Although FISH is a powerful technology for identifying NTRK rearrangements, RNA-/DNA-based NGS is recommended for highly suspected cases in which FISH signal patterns are not discernible as classic positive patterns, particularly if targeted therapy is considered.

Primary Malignant Peripheral Nerve Sheath Tumor of the Stomach: A Rare Case Report and Review of Literature

Malignant peripheral nerve sheath tumor (MPNST) is a spindle cell sarcoma originating from peripheral nerves or showing differentiation of nerve sheath components. Primary MPNST of the stomach is an extremely rare neoplasm with only a few published reports in the literature. We present the case of a 58-year-old male patient with MPNST in the stomach. The patient was admitted due to upper abdomen discomfort. Gastroscopy revealed a huge ulcer lesion in the stomach, and biopsy revealed a spindle cell malignant neoplasm. No other specific findings were found in the whole-body imaging examination. Subtotal gastrectomy was performed. Histologically, an ulcer-type, push-infiltrating mass composed of dense, woven-like spindle cells with frequent mitosis could be seen. In immunohistochemistry, the tumor cells were negative for expression of H3K27 trimethylation (H3K27me3), keratin (AE1/AE3), epithelial membrane antigen (EMA), CD34, KIT, DOG1 (ANO1), S-100, SOX10, smooth muscle actin, desmin, myogenin, MDM2, CDK4, P16 (CDKN2A) and SS18-SSX (SS18::SSX). Primary MPNST of the stomach was diagnosed based on histological and immunohistochemical results. During the 2.5 years follow-up period after surgery, no recurrence was observed.

The Recent Advances in Molecular Diagnosis of Soft Tissue Tumors

Soft tissue tumors are rare mesenchymal tumors with divergent differentiation. The diagnosis of soft tissue tumors is challenging for pathologists owing to the diversity of tumor types and histological overlap among the tumor entities. Present-day understanding of the molecular pathogenesis of soft tissue tumors has rapidly increased with the development of molecular genetic techniques (e.g., next-generation sequencing). Additionally, immunohistochemical markers that serve as surrogate markers for recurrent translocations in soft tissue tumors have been developed. This review aims to provide an update on recently described molecular findings and relevant novel immunohistochemical markers in selected soft tissue tumors.

Low expression of H3K27me3 is associated with poor prognosis in conventional chordoma

Purpose

Chordoma is a rare and locally invasive neoplasm, and the prognostic factors are limited. Deregulation of Histone 3 lysine 27 (H3K27) trimethylation (H3K27me3) is considered to be related with poor prognosis in some tumors. The purpose of this study was to detect the expression of H3K27me3 in chordomas and analyze the correlation with clinicopathological features and explore the roles as potential prognostic markers and therapeutic targets.

Material and method

Specimens of 162 chordoma patients (consisting of 156 conventional chordoma, 4 dedifferentiated chordoma and 2 poorly differentiated chordoma) were enrolled in a tissue microarray (TMA) in order to assess the immunohistochemical staining by H3K27me3 antibodies. Correlations between H3K27me3 expression and clinicopathological features were analyzed. Clinical data of the patients were correlated and survival analysis was performed. Kaplan-Meier survival curves and log-rank test were used to analyze the recurrence-free survival (RFS) and overall survival (OS). Multivariate Cox regression analyses were used to identify potential prognostic factors.

Results

The expression of H3K27me3 was lower in 37 chordoma patients (37/162, 22.8%), and higher in 125 patients (125/162, 77.2%). H3K27me3-low expression significantly correlated with spine location (P < 0.001), conventional histological subtype (P < 0.001), and recurrence (P < 0.001). Log-rank test showed that H3K27me3-low expression was associated with poor RFS (P =0.027) and OS (P =0.009) in conventional chordoma patients. Cox multivariate analysis revealed that low expression of H3K27me3 was an independent predictor of poor OS (P =0.007) and RFS (P =0.025) in conventional chordoma patients.

Conclusions

Our study indicates that low expression of H3K27me3 might be considered as a predictor for poor prognosis and recurrence, and it may provide a potential therapeutic target for conventional chordoma patients.

Histone H3 K27 alterations in central nervous system tumours: Challenges and alternative diagnostic approaches

Upon the discovery of frequent oncogenic histone alterations in paediatric diffuse high-grade gliomas, the epigenetic and transcriptional landscapes of tumours have become increasingly important aspects of diagnostic and prognostic analysis. The replacement of lysine 27 with methionine in H3 histone variants - H3 p.K28M (K27M) - was the first reported histone mutation associated with human malignancies, seen in up to 80% of paediatric diffuse midline gliomas. This discovery contributed to the updated 2021 World Health Organization (WHO) classification of central nervous system (CNS) tumours in which paediatric diffuse high-grade gliomas were classified into molecular-based categories. Therefore, molecular analysis of tumour cells has become increasingly necessary for determining disease prognosis and potential therapeutic strategies. Although detection of histone alterations is crucial for the diagnosis of specific glioma subtypes, several studies have identified them in other CNS tumours, which may be misleading during routine diagnostic work. While traditional biopsies remain the standard for diagnosis of gliomas, they pose a high risk for surgical complications and patient morbidity. Consequently, this review highlights the importance of the H3 K27-alterations in paediatric gliomas and several other CNS tumours. We also discuss the potential of liquid biopsies as a minimally invasive and highly effective alternative for confirming the diagnosis and potential targeted epigenetic therapies which may improve the survival of patients.

Primary Urethral Malignant Peripheral Neural Sheath Tumor in a 58-Year-Old Female in the Absence of Neurofibromatosis Type 1

A malignant peripheral neural sheath tumor (MPNST) is a malignant soft tissue neoplasm with cellular origin arising from the outer lining of peripheral nerves. Approximately 10 cases have been identified to date where the lower urinary tract was affected. We discuss the case of a female patient that presented with primary MPNST that arose in the urethral tract in the absence of neurofibromatosis type 1 (NF1) or prior malignancies. This patient presented with pain and acute urinary tract symptoms secondary to urethral obstruction by a protruding vaginal mass. The patient underwent an incomplete initial resection to alleviate symptoms and to obtain a tissue diagnosis. Three months after the first hospitalization, the patient was re-hospitalized due to the recurrence of symptoms and subsequently underwent a complete tumor excision. The initial resection showed a 7.0 x 4.5 x 4.5 cm aggregate of tan-red to gray tumor masses. Microscopic examination showed a spindle cell neoplasm with malignant cytological features (hypercellularity, atypical mitoses, nuclear pleomorphism, and indistinct borders). Tumor cells stained positive for SOX10, S-100 (10% of tumor), with a "mosaic pattern" of H3K27ME3 (50% of tumor nuclei positive). Other lineage-specific and keratin markers stained negative. In the absence of other patient known primaries, the findings were consistent with a primary MPNST of the urinary tract. Residual tumor was identified on MRI scans one month after the follow-up. The completely excised tumor specimen on the second admission showed identical morphology when compared to the first specimen. While MPNSTs typically carry a poor prognosis, knowledge of behavior and prognosis of primary MPNSTs in the bladder is limited, due to the few relative numbers of available case reports. Further research is needed to study the clinical behavior, morphology, immunophenotypes, and genetics of primary MPNSTs arising from the lower urinary tract.

Oncogenic Roles of Polycomb Repressive Complex 2 in Bladder Cancer and Upper Tract Urothelial Carcinoma

Cancers of the urinary tract are one of the most common malignancies worldwide, causing high morbidity and mortality, and representing a social burden. Upper tract urothelial carcinoma (UTUC) accounts for 5−10% of urinary tract cancers, and its oncogenic mechanisms remain elusive. We postulated that cancers of the lower and the upper urinary tract may share some important oncogenic mechanisms. Therefore, the oncogenic mechanisms discovered in the lower urinary tract may guide the investigation of molecular mechanisms in the upper urinary tract. Based on this strategy, we revisited a high-quality transcriptome dataset of 510 patients with non-muscle invasive bladder cancer (NMIBC), and performed an innovative gene set enrichment analysis of the transcriptome. We discovered that the epigenetic regulation of polycomb repressive complex 2 (PRC2) is responsible for the recurrence and progression of lower-track urinary cancers. Additionally, a PRC2-related gene signature model was discovered to be effective in classifying bladder cancer patients with distinct susceptibility of subsequent recurrence and progression (log-rank p < 0.001 and = 0.001, respectively). We continued to discover that the same model can differentiate stage T3 UTUC patients from stage Ta/T1 patients (p = 0.026). Immunohistochemical staining revealed the presence of PRC2 components (EZH2, EED, and SUZ12) and methylated PRC2 substrates (H3K27me3) in the archived UTUC tissues. The H3K27me3 exhibited higher intensity and area intensity product in stage T3 UTUC tissues than in stage Ta/T1 tissues (p = 0.006 and 0.015, respectively), implicating stronger PRC2 activity in advanced UTUC. The relationship between H3K27 methylation and gene expression is examined using correlations. The H3K27me3 abundance is positively correlated with the expression levels of CDC26, RP11-2B6, MAPK1IP1L, SFR1, RP11-196B3, CDK5RAP2, ANXA5, STX11, PSMD5, and FGFRL1. It is also negatively correlated with CNPY2, KB-1208A12, RP11-175B9, ZNF692, RANP8, RP11-245C17, TMEM266, FBXW9, SUGT1P2, and PRH1. In conclusion, PRC2 and its epigenetic effects are major oncogenic mechanisms underlying both bladder cancer and UTUC. The epigenetically regulated genes of PRC2 in urothelial carcinoma were also elucidated using correlation statistics.

Loss of H3K27me3 expression in canine nerve sheath tumors

Nerve sheath tumors (NSTs) are characterized by neoplastic proliferation of Schwann cells, perineurial cells, endoneurial and/or epineurial fibroblasts. Diagnosis of NST is often challenging, particularly in distinguishing malignant NST (MNST) from other soft tissue sarcomas, or sometimes between low-grade MNST and benign NST. Recent studies in human pathology have demonstrated loss of trimethylation at lysine 27 of histone 3 (H3K27me3) in a subset of MNSTs using immunohistochemistry. Loss of H3K27me3 expression is rare in other high-grade sarcomas and also appears to be useful in distinguishing benign and low-grade MNSTs from high-grade subsets. In our retrospective study, we performed H3K27me3 immunohistochemistry in 68 canine tumors previously diagnosed as NST. We detected loss of H3K27me3 expression in 25% (n = 17) of all canine NST, including one neurofibroma, whereas 49% (n = 33) of tumors had mosaic loss of expression and 26% (n = 18) retained expression. No statistically significant differences were found between H3K27me3 expression, histopathological features of tumors, and their immunoreactivity for Sox10, claudin-1, GFAP, and Ki67. Because the classification of canine NST is not yet fully established and its correlation with the prognosis and clinical course of the disease is lacking, prospective studies with possible genetic analyses are needed to assess the true diagnostic value of H3K27me3 loss in canine NST.

CDX2 expression in malignant peripheral nerve sheath tumour: a potential diagnostic pitfall associated with PRC2 inactivation

AIMS

Malignant peripheral nerve sheath tumour (MPNST) is a soft tissue sarcoma that exhibits features of Schwann cell differentiation. Heterologous, often mesenchymal-type differentiation occurs in a subset of MPNST, while glandular morphology also is encountered in rare cases. We observed in MPNST unanticipated expression of CDX2, a transcription factor that regulates intestinal epithelial differentiation, and aimed to further characterize this phenomenon.

METHODS/RESULTS

Expression of CDX2 was assessed by immunohistochemistry in a total of 32 high-grade MPNSTs lacking morphological evidence of epithelial differentiation, including twelve tumours (38%) that developed in the setting of neurofibromatosis and four (13%) in the setting of prior radiation therapy. CDX2 was expressed by 14 of 32 MPNSTs (44%), wherein immunoreactivity, varying from weak to strong, was present in 2-95% of neoplastic spindle cells (median 10%, mean 23%). Notably, CDX2 expression was limited to tumours with PRC2 inactivation (22/32; 69%), as evidenced immunohistochemically by diffuse loss of trimethylated histone H3K27. Analysing publicly available RNA-sequencing data from twelve MPNST cell lines, two of which are clonally related, we observed CDX2 expression in all six PRC2-inactivated cell lines, while CDX2 expression was negligible in six cell lines with intact PRC2, amounting to a 58-fold increase in CDX2 expression on average with PRC2 inactivation.

CONCLUSIONS

CDX2 is expressed in a subset of MPNSTs, even in the absence of morphological evidence of epithelial differentiation. CDX2 expression in MPNST is strongly associated with underlying PRC2 inactivation.

Clinicopathological and prognostic significance of H3K27 methylation status in malignant peripheral nerve sheath tumor: correlation with skeletal muscle differentiation

Malignant peripheral nerve sheath tumor (MPNST) is a very aggressive peripheral nerve sheath-derived sarcoma, which is one of the most difficult tumors to diagnose due to its wide spectrum of histological findings and lack of specific immunohistochemical markers. Recently, it has been reported that losses of expression of H3K27me3 and H3K27me2 caused by PRC2 dysfunction may be useful diagnostic markers for MPNST, but there is no consensus on their clinicopathological significance. Here, we investigated the relationship between loss of H3K27 methylation and various parameters and clarified the clinicopathological significance of such loss. We analyzed the clinicopathological and immunohistochemical features in 84 MPNST cases. Complete losses of H3K27me3 and H3K27me2 were observed in 37 (44%) and 29 (35%) cases, respectively. Losses of H3K27me3 and H3K27me2 were significantly correlated with myogenic immunopositivity (H3K27me3 vs. desmin, P = 0.0051; H3K27me3 vs. myogenin, P = 0.0009; H3K27me2 vs. myogenin, P = 0.042). Meanwhile, there were significant correlations between preservation of immunohistochemical neurogenic markers and intact H3K27me3 and H3K27me2 (H3K27me3 vs. S-100 protein, P = 0.0019; H3K27me3 vs. SOX10, P = 0.014; H3K27me2 vs. S-100 protein, P = 0.0011; H3K27me2 vs. SOX10, P = 0.0087). In multivariate analysis, local recurrence, distant metastasis, high FNCLCC grade, and loss of SOX10 expression were independent prognostic factors for overall survival. H3K27me3 and H3K27me2 expression was retained in all 26 cases of rhabdomyosarcoma non-alveolar subtype. In conclusion, we suggest that H3K27me3 and H3K27me2 immunonegativity is useful but not definitive for diagnosing MPNST. Complete loss of H3K27 methylation may be involved in aggressive transdifferentiation from neural differentiation to skeletal muscle differentiation in MPNST.

The substantial loss of H3K27me3 can stratify risk in grade 2, but not in grade 3 meningioma

Trimethylation of lysine 27 of histone H3 (H3K27me3) has recently emerged as a crucial epigenetic marker in meningioma. The loss of H3K27me3 expression might predict the early recurrence of grade 1 and 2 meningiomas. However, this is controversial in terms of grade 3 meningioma and the effects of H3K27me3 on the overall survival (OS) of patients with low low-grade meningioma have not been studied. Therefore, we immunohistochemically assessed the prognostic implications of H3K27me3 expression in grade 2 and 3 meningiomas. Whole-slide H3K27me3 immunostaining was evaluated for strict quality control and to confirm a significant correlation (P < .0001) with tissue microarray results. The effects of tissue age on H3K27me3 immunostaining were also evaluated, to select an appropriate cohort for survival analysis. Log-rank tests of 115 grade 2 meningiomas and 26 grade 3 meningiomas showed that the loss of H3K27me3 expression was a prognostic factor for early recurrence (P < .0001) and death (P = .00012) in grade 2, but not in grade 3 meningioma. Multivariate analysis revealed that age, recurrent tumor, and loss of H3K27me3 expression (hazard ratio, 1.264-7.510; P = .0133) were significant for recurrentrecurrence-free survival (RFS), and that recurrent tumor and loss of H3K27me3 expression (hazard ratio, 1.717-120.621; P = .0140) were significant for OS. We concluded that H3K27me3 expression is a significant prognostic factor for the RFS and OS of patients with grade 2 meningioma; it should be considered as an ancillary test for risk stratification of this meningioma.

Poorly-differentiated and undifferentiated sarcomas of the mediastinum: a bag of tricks

Mediastinum is a Pandora's Box containing many different structures that can give origin to several cancer types. Our aims are to provide a general framework to make a diagnosis of an undifferentiated pleomorphic sarcoma and to highlight relevant immunohistochemical and molecular techniques that can help in the differential diagnosis. We, therefore, provide a simple three-step algorithmic approach to diagnose pleomorphic sarcoma, emphasizing the role of clinicopathological correlations and advocating for a "relative frequency" method, especially when the material for the diagnosis is scarce, as in small biopsies. In the first place, if clinical and/or radiological features make a non-sarcoma diagnosis more likely, it should be ruled in. Next, even if no specific non-sarcomatous diagnoses are suspected, they should always be ruled out. Lastly, since many sarcomas can have a pleomorphic appearance, specific entities should also be ruled out because their identification might affect prognosis and treatment. We then cover selected immunohistochemical and molecular ancillary tests that can come at hand in the diagnosis, highlighting the pros and cons; in particular the use and the limitations of H3K27me3 immunohistochemistry, the meaning of MDM2 amplification in the mediastinum and the implication of muscle differentiation-either smooth or skeletal-in sarcomas. The main take home messages are to always rule-out more frequent lesion first and always include clinical and radiological information in the diagnostic process.

Loss of H3K27me3 occurs in a large subset of embryonal rhabdomyosarcomas: Immunohistochemical and molecular analysis of 25 cases

Loss of histone 3 lysine 27 trimethylation (H3K27me3) has been described as a diagnostic marker for malignant peripheral nerve sheath tumor (MPNST), also discriminating MPNST with rhabdomyoblastic differentiation (malignant Triton tumor) from rhabdomyosarcoma (RMS). We studied the immunohistochemical expression of H3K27me3 in embryonal RMSs (ERMSs), performed methylation profiling in order to support the diagnosis and RNA-sequencing for comparison of the transcriptome of H3K27me3-positive and -negative cases. Of the 25 ERMS patients, 17 were males and 8 were females with an age range from 1 to 67 years (median, 6 years). None were known with neurofibromatosis type 1. One patient had Li-Fraumeni syndrome. Tumor localization included paratesticular (n = 9), genitourinary (n = 6), head/neck (n = 5), retroperitoneal (n = 4) and lower arm (n = 1). Five MPNSTs served as reference group. All ERMS had classical features including a variable spindle cell component. Immunohistochemical loss (partial or complete) of H3K27me3 was detected in 18/25 cases (72%). Based on methylation profiling, 22/22 cases were classified as ERMS. Using RNA sequencing, the ERMS group (n = 14) had a distinct gene expression profile in contrast to MPNSTs, confirming that the H3K27me3 negative ERMS cases do not represent malignant Triton tumors. When comparing H3K27me3-negative and -positive ERMSs, gene set enrichment analysis revealed differential expression of genes related to histone acetylation and normal muscle function with H3K27me3 negative ERMSs being associated with acetylation. Conclusion: Loss of H3K27me3 frequently occurs in ERMSs and correlates with H3K27 acetylation. H3K27me3 is not a suitable marker to differentiate ERMS (with spindle cell features) from malignant Triton tumor.

Prognostic Significance of Immunohistochemical Markers and Genetic Alterations in Malignant Peripheral Nerve Sheath Tumors: A Systematic Review

Background

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft tissue sarcomas with dismal prognosis. Pathological and genetic markers may predict more aggressive behavior in MPNSTs but have uncommonly been investigated, and few are used in daily practice. This study reviews the prognostic value of immunohistochemical markers and genetic alterations in MPNST.

Methods

A systematic search was performed in PubMed and Embase databases according to the PRISMA guidelines. Search terms related to ‘MPNST’ and ‘prognostic’ were used. Studies investigating the association of immunohistochemical markers or genetic alterations with prognosis were included. Qualitative synthesis was performed on all studies. A distinction was made between univariable and multivariable associations.

Results

Forty-six studies were included after full-text screening. Sixty-seven different immunohistochemical markers were investigated. Absence of S100 and H3K27me3 and high Ki67 and p53 staining was most commonly independently associated with worse survival and disease-free survival. Several genetic alterations were investigated as well with varying association to survival. TP53, CDK4, RASSF1A alterations were independently associated with worse survival, as well as changes in chromosomal length in Xp, 10q, and 16p.

Conclusions

MPNSTs harbor complex and heterogeneous biology. Immunohistochemical markers and genetic alterations have variable prognostic value. Absence of S100 and H3K27me3 and increased Ki67 can be of prognostic value. Alterations in TP53 or increase in p53 staining may distinguish MPNSTs with worse outcomes. Genetic alterations and staining of other cell cycle regulatory and Ras pathway proteins may also help stratifying patients with worse outcomes. A combination of markers can increase the prognostic value.

Loss of histone H3 trimethylation on lysine 27 and nuclear expression of transducin-like enhancer 1 in primary intracranial sarcoma, DICER1-mutant

AIMS

Primary intracranial sarcoma, DICER1-mutant is a recently described central nervous system tumour with specific genomic and DNA-methylation profiles. Although some of its histological features (focal spindle-cell morphology, intracytoplasmic eosinophilic granules, and focal heterologous differentiation) are common across most reported cases, the presence of significant histological variability and the lack of differentiation pose diagnostic challenges. We aim to further define the immunoprofile of this tumor.

METHODS AND RESULTS

We reviewed the clinical history and performed immunohistochemistry for glial fibrillary acidic protein, oligodendrocyte transcription factor 2, SOX2, SOX10, S100, histone H3 trimethylated on lysine 27 (H3K27me3), desmin, myogenin, CD99, epithelial membrane antigen (EMA) and transducin-like enhancer of split 1 (TLE1) on six primary intracranial sarcomas, DICER1-mutant, with appropriate controls. Targeted exome sequencing was performed on all cases. The sarcomas showed diffuse (n = 4), mosaic (n = 1) or minimal (≤5%, n = 1) loss of H3K27 trimethylation and nuclear TLE1 expression (n = 6). Four had immunohistochemical evidence of myogenic differentiation. SOX2, SOX10, S100 and EMA were negative; CD99 expression ranged from focal cytoplasmic (n = 4) to crisp diffuse membranous (n = 2). One tumour had focal cartilaginous differentiation. Similar immunohistochemical findings were observed in a pleuropulmonary blastoma (albeit with focal TLE1 expression), a DICER1-related pineoblastoma, and an embryonal tumour with a multilayered rosette-like DICER1-related cerebellar tumour. Targeted exome sequencing confirmed the presence of pathogenic biallelic DICER1 mutations in all tumours included in this study.

CONCLUSION

We conclude that H3K27me3 and TLE1 immunostains, when utilised in combination, can be helpful diagnostic markers for primary intracranial sarcoma, DICER1-mutant.

Radiation-associated sarcomas other than malignant peripheral nerve sheath tumours demonstrate loss of histone H3K27 trimethylation†

BACKGROUND AND AIMS

Complete loss of histone H3 lysine 27 trimethylation (H3K27me3) has recently emerged as a biomarker for malignant peripheral nerve sheath tumours (MPNST). Loss of H3K27me3 staining has also been reported in post-radiation MPNST; however, it has not been evaluated in a large series of radiation-associated sarcomas of different histological subtypes. The aim of this study was to assess H3K27me3 labelling by immunohistochemistry in radiation-associated sarcomas and to determine the prevalence of H3K27me3 loss in these tumours.

METHODS AND RESULTS

Radiation-associated sarcomas (n = 119) from two tertiary care referral centres were evaluated for loss of H3K27me3, defined as complete loss of staining within tumour cells in the presence of a positive internal control. Twenty-three cases (19%) showed H3K27me3 loss, including nine of 10 (90%) MPNST, seven of 77 (9%) undifferentiated spindle cell/pleomorphic sarcomas, five of 25 (20%) angiosarcomas, one of five (20%) leiomyosarcomas and one of two (50%) osteosarcomas.

CONCLUSIONS

Complete H3K27me3 loss was present in 19% of radiation-associated sarcomas in our series. Our findings demonstrate that loss of H3K27me3 is not specific for radiation-associated MPNST and may also occur in other histological subtypes of RAS, including radiation-associated undifferentiated spindle cell/pleomorphic sarcoma, angiosarcoma, leiomyosarcoma and osteosarcoma.

Histopathologic findings in malignant peripheral nerve sheath tumor predict response to radiotherapy and overall survival

Background

Malignant peripheral nerve sheath tumor (MPNST) is an aggressive and poorly understood malignant neoplasm. Even in the setting of multimodal therapy, the clinical course of MPNST is frequently marked by metastatic conversion and poor overall prognosis, with optimal treatment paradigms for this rare tumor unknown.

Methods

We reviewed the medical records and histopathology of 54 consecutive patients who were treated at University of California San Francisco between 1990 and 2018.

Results

Our cohort consisted of 24 male and 30 female patients (median age 38 years). Fédération Nationale des Centres de Lutte Contre Le Cancer (FNCLCC) sarcoma grading criteria segregated patients into groups with differences in overall survival (OS) (P = .02). Increasing Ki-67 labeling index was associated with poor OS (hazard ratio [HR] 1.36 per 10%, P = .0002). Unsupervised hierarchical clustering-based immunohistochemical staining patterns identified 2 subgroups of tumors with differences in H3K27me3, Neurofibromin, S100, SOX10, p16, and EGFR immunoreactivity. In our cohort, cluster status was associated with improved locoregional failure-free rate (P = .004) in response to radiation.

Conclusions

Our results lend support to the FNCLCC sarcoma grading criteria as a prognostic scheme for MPNST, although few cases of grade 1 were included. Further, we identify increased Ki-67 labeling as a strong predictor of poor OS from MPNST. Finally, we identify a subset of MPNSTs with a predictive immunohistochemical profile that has improved local control with adjuvant radiotherapy. These data provide insights into the grading and therapy for patients with MPNST, although further studies are needed for independent validation.

H3K27me3 expression and methylation status in histological variants of malignant peripheral nerve sheath tumours

Diagnosing MPNST can be challenging, but genetic alterations recently identified in polycomb repressive complex 2 (PRC2) core component genes, EED and SUZ12, resulting in global loss of the histone 3 lysine 27 trimethylation (H3K27me3) epigenetic mark, represent drivers of malignancy and a valuable diagnostic tool. However, the reported loss of H3K27me3 expression ranges from 35% to 84%. We show that advances in molecular pathology now allow many MPNST mimics to be classified confidently. We confirm that MPNSTs harbouring mutations in PRC2 core components are associated with loss of H3K27me3 expression; whole‐genome doubling was detected in 68%, and SSTR2 was amplified in 32% of MPNSTs. We demonstrate that loss of H3K27me3 expression occurs overall in 38% of MPNSTs, but is lost in 76% of histologically classical cases, whereas loss was detected in only 23% cases with heterologous elements and 14% where the diagnosis could not be provided on morphology alone. H3K27me3 loss is rarely seen in other high‐grade sarcomas and was not found to be associated with an inferior outcome in MPNST. We show that DNA methylation profiling distinguishes MPNST from its histological mimics, was unrelated to anatomical site, and formed two main clusters, MeGroups 4 and 5. MeGroup 4 represents classical MPNSTs lacking H3K27me3 expression in the majority of cases, whereas MeGroup 5 comprises MPNSTs exhibiting non‐classical histology and expressing H3K27me3 and cluster with undifferentiated sarcomas. The two MeGroups are distinguished by differentially methylated PRC2‐associated genes, the majority of which are hypermethylated in the promoter regions in MeGroup 4, indicating that the PRC2 target genes are not expressed in these tumours. The methylation profiles of MPNSTs with retention of H3K27me3 in MeGroups 4 and 5 are independent of mutations in PRC2 core components and the driver(s) in these groups remain to be identified. Our results open new avenues of investigation. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Variable Expression of S100 Protein in Sinonasal Malignant Mucosal Melanoma: A Potential Diagnostic Pitfall

Sinonasal malignant mucosal melanoma (SNM) is a rare, aggressive malignancy. The diagnosis of SNM is often quite challenging due to anatomical limitations, frequent lack of pigmentation, variable histologic appearances, and aberrant differentiation (e.g., positivity for cytokeratin, desmin, or neuroendocrine markers). S100 protein is routinely used as a standard screening marker for SNM, but it may lack optimal sensitivity. Our objective was to study the extent of immunohistochemical expression of S100 protein in SNM, and determine its diagnostic value by comparing it to a newer melanoma marker, SOX10. Twenty-three cases of sinonasal MMM were retrieved from the archival files of the Department of Pathology at UT Southwestern Medical Center. The patients included 14 men and 9 women, and ranged from 36 to 90 years (mean 64.9 years). Sections from blocks of formalin-fixed, paraffin-embedded tissue were used for immunohistochemical analysis with S100 protein and SOX10. The extent and intensity of immunostaining was recorded, and H-score was calculated. For a subset of negative or focally positive cases, S100 protein was repeated at a high-volume reference laboratory. S100 protein immunoexpression was quite variable in the SNM cases, with H-scores ranging from 0 to 300 (mean 123). While 11 of 23 cases exhibited strong and diffuse staining (H-score > 100) as expected for melanoma, 7 were weak and/or focal (H-score 1-100), and 5 were completely S100 protein-negative. For 10 cases, the negative or focal results were confirmed by reference laboratory staining. In contrast, all 23 SNM cases were diffusely and strongly positive for SOX10 (H-scores 210-300, mean 296). Our study demonstrated that S100 protein immunoexpression is extremely variable in SNM. Weak or even absent S100 protein staining is not uncommon in SNM, and should not dissuade pathologists from that diagnosis. Our data demonstrates that S100 protein is insufficiently sensitive to be used as a screening marker for SNM, but that SOX10 is consistently and robustly positive, and should therefore replace S100 protein for that purpose. Indeed, for any high-grade sinonasal tumor, pathologists must have a low threshold for utilizing additional markers to exclude the possibility of SNM.

The Role of Polycomb Repressive Complex in Malignant Peripheral Nerve Sheath Tumor

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive soft tissue sarcomas that can arise most frequently in patients with neurofibromatosis type 1 (NF1). Despite an increasing understanding of the molecular mechanisms that underlie these tumors, there remains limited therapeutic options for this aggressive disease. One potentially critical finding is that a significant proportion of MPNSTs exhibit recurrent mutations in the genes EED or SUZ12, which are key components of the polycomb repressive complex 2 (PRC2). Tumors harboring these genetic lesions lose the marker of transcriptional repression, trimethylation of lysine residue 27 on histone H3 (H3K27me3) and have dysregulated oncogenic signaling. Given the recurrence of PRC2 alterations, intensive research efforts are now underway with a focus on detailing the epigenetic and transcriptomic consequences of PRC2 loss as well as development of novel therapeutic strategies for targeting these lesions. In this review article, we will summarize the recent findings of PRC2 in MPNST tumorigenesis, including highlighting the functions of PRC2 in normal Schwann cell development and nerve injury repair, as well as provide commentary on the potential therapeutic vulnerabilities of a PRC2 deficient tumor cell.

Low doses of deoxynivalenol inhibit the cell migration mediated by H3K27me3-targeted downregulation of TEM8 expression

Deoxynivalenol (DON) is a mycotoxin produced by multipleFusariumspecies that often contaminates cereals and threatens human and animal health. A wide range of cytotoxic effects, such as the induction of DNA damage, an increase in mitochondrial permeability and the inhibition of macromolecule synthesis, have been reported. However, the effects of DON on cell migration-a fundamental process in living cells critical for normal development, immune responses, and disease processes-and the mechanism underlying these effects are still unclear. Here, we showed that DONsignificantly inhibited the migration of MRC-5, CCD-18Co, HCT116 and WM793 cells at 50 ng/ml, 50 ng/ml, 400 ng/ml and 250 ng/ml, respectively, which maintained cell viability at 90%. Further analysis showed that DON inhibited the expression of tumour endothelial marker 8 (TEM8), a key gene in cell migration. Furthermore, we showed that DON inhibited the expression of TEM8 through increasing the level of H3K27me3 in the TEM8 promoter. Finally, overexpression of TEM8 or treating by H3K27me3-specific inhibitor GSK126 attenuated the inhibitory effect of DON on cell migration. In summary, low doses of DON at approximately dietary exposure significantly inhibited cell migration by downregulating the expression of TEM8 in a manner mediated by H3K27me3, which may generate increasing concerns for the risk of DON exposure.

Soft Tissue Special Issue: Biphenotypic Sinonasal Sarcoma: A Review with Emphasis on Differential Diagnosis

Biphenotypic sinonasal sarcoma is an anatomically restricted low-grade malignant neoplasm with dual neural and myogenic differentiation composed of a monotonous population of spindled cells with herringbone/fascicular architecture. These tumors demonstrate a unique immunoprofile with relatively consistent S100-protein and actin expression in conjunction with more variable desmin, myogenin and myoD1 staining. SOX10 is uniformly negative. Genetically, the majority of tumors harbor PAX3-MAML3 fusions, with alternate PAX3 partners including FOXO1, NCOA1, NCOA2 and WWTR1. Although the differential diagnosis of BSNS is broad, careful morphologic inspection together with targeted ancillary studies is often sufficient to arrive at the correct diagnosis. As these tumors have significant local recurrence rates but lack metastatic potential, awareness and accurate diagnosis of this rare and newly described neoplasm is critical for appropriate management.

HYPERsol: High-Quality Data from Archival FFPE Tissue for Clinical Proteomics

Massive formalin-fixed, paraffin-embedded (FFPE) tissue archives exist worldwide, representing an invaluable resource for clinical proteomics research. However, current protocols for FFPE proteomics lack standardization, efficiency, reproducibility, and scalability. Here we present high-yield protein extraction and recovery by direct solubilization (HYPERsol), an optimized workflow using ultrasonication and S-Trap sample processing that enables proteome coverage and quantification from FFPE samples comparable to that achieved from flash-frozen tissue (average R = 0.936). When applied to archival samples, HYPERsol resulted in high-quality data from FFPE specimens in storage for up to 17 years, and may enable the discovery of new immunohistochemical markers.

Histone H3K27 dimethyl loss is highly specific for malignant peripheral nerve sheath tumor and distinguishes true PRC2 loss from isolated H3K27 trimethyl loss

Malignant peripheral nerve sheath tumors contain loss of histone H3K27 trimethylation (H3K27me3) due to driver mutations affecting the polycomb repressive complex 2 (PRC2). Consequently, loss of H3K27me3 staining has served as a diagnostic marker for this tumor type. However, recent reports demonstrate H3K27me3 loss in numerous other tumors, including some in the differential diagnosis of malignant peripheral nerve sheath tumor. Since these tumors lose H3K27me3 through mechanisms distinct from PRC2 loss, we set out to determine whether loss of dimethylation of H3K27, which is also catalyzed by PRC2, might be a more specific marker of PRC2 loss and malignant peripheral nerve sheath tumor. Using mass spectrometry, we identify a near complete loss of H3K27me2 in malignant peripheral nerve sheath tumors and cell lines. Immunohistochemical analysis of 72 malignant peripheral nerve sheath tumors, seven K27M-mutant gliomas, 43 ependymomas, and 10 Merkel cell carcinomas demonstrates that while H3K27me3 loss is common across these tumor types, H3K27me2 loss is limited to malignant peripheral nerve sheath tumors and is highly concordant with H3K27me3 loss (33/34 cases). Thus, increased specificity does not come at the cost of greatly reduced sensitivity. To further compare H3K27me2 and H3K27me3 immunohistochemistry, we investigated 42 melanomas and 54 synovial sarcomas, histologic mimics of malignant peripheral nerve sheath tumor with varying degrees of H3K27me3 loss in prior reports. While global H3K27me3 loss was not seen in these tumors, weak and limited H3K27me3 staining was common. By contrast, H3K27me2 staining was more clearly retained in all cases, making it a superior binary classifier. This was confirmed by digital image analysis of stained slides. Our findings indicate that H3K27me2 loss is highly specific for PRC2 loss and that PRC2 loss is a rarer phenomenon than H3K27me3 loss. Consequently, H3K27me2 loss is a superior diagnostic marker for malignant peripheral nerve sheath tumor.

Telomere alterations in neurofibromatosis type 1-associated solid tumors

The presence of Alternative lengthening of telomeres (ALT) and/or ATRX loss, as well as the role of other telomere abnormalities, have not been formally studied across the spectrum of NF1-associated solid tumors. Utilizing a telomere-specific FISH assay, we classified tumors as either ALT-positive or having long (without ALT), short, or normal telomere lengths. A total of 426 tumors from 256 NF1 patients were evaluated, as well as 99 MPNST tumor samples that were sporadic or of unknown NF1 status. In the NF1-glioma dataset, ALT was present in the majority of high-grade gliomas: 14 (of 23; 60%) in contrast to only 9 (of 47; 19%) low-grade gliomas (p = 0.0009). In the subset of ALT-negative glioma cases, telomere lengths were estimated and we observed 17 (57%) cases with normal, 12 (40%) cases with abnormally long, and only 1 (3%) case with short telomeres. In the NF1-associated malignant nerve sheath tumor (NF1-MPNST) set (n = 75), ALT was present in 9 (12%). In the subset of ALT-negative NF1-MPNST cases, telomeres were short in 9 (38%), normal in 14 (58%) and long in 1 (3%). In the glioma set, overall survival was significantly decreased for patients with ALT-positive tumors (p < 0.0001). In the NF1-MPNST group, overall survival was superior for patients with tumors with short telomeres (p = 0.003). ALT occurs in a subset of NF1-associated solid tumors and is usually restricted to malignant subsets. In contrast, alterations in telomere lengths are more prevalent than ALT.

Very Unusual Sellar/Suprasellar Region Masses: A Review

The cause of sellar region masses in large retrospective series is overwhelmingly pituitary adenomas (84.6%), followed by craniopharyngiomas (3.2%), cystic nonneoplastic lesions (2.8%), inflammatory lesions (1.1%), meningiomas (0.94%), metastases (0.6%), and chordomas (0.5%) (1). While other rare lesions were also identified (collectively 6.0%), single unusual entities in the above-cited series numbered <1-2 examples each out of the 4122 cases, underscoring their rarity. We searched our joint files for rare, often singular, sellar/suprasellar masses that we had encountered over the past several decades in our own specialty, tertiary care specialty pituitary center practices. Cases for this review were subjectively selected for their challenging clinical and/or histological features as well as teaching value based on the senior authors' (MBSL, BKD) collective experience with over 7000 examples. We excluded entities deemed to be already well-appreciated by neuropathologists such as mixed adenoma-gangliocytoma, posterior pituitary tumors, metastases, and hypophysitis. We identified examples that, in our judgment, were sufficiently unusual enough to warrant further reporting. Herein, we present 3 diffuse large cell B cell pituitary lymphomas confined to the sellar region with first presentation at that site, 2 sarcomas primary to sella in nonirradiated patients, and 1 case each of granulomatosis with polyangiitis and neurosarcoidosis with first presentations as a sellar/suprasellar mass. Other cases included 1 of chronic lymphocytic leukemia within a gonadotroph adenoma and 1 of ectopic nerve fascicles embedded within a somatotroph adenoma, neither of which impacted patient care. Our objective was to share these examples and review the relevant literature.

EWSR1-SMAD3 positive fibroblastic tumor

We present a case of EWSR1-SMAD3 positive fibroblastic tumor that occurred in a 24-year-old man who presented with a recurrent tumor in the dorsum of his right foot. Magnetic resonance imaging (MRI) demonstrated a subcutaneous nodule located in the third metatarsophalangeal joint region, measuring 10 × 8 × 5 mm in size. Histological examination revealed a monomorphic spindle cell tumor composed of cellular fascicles of bland fibroblasts with hyalinization. Immunohistochemically, the tumor showed diffuse nuclear staining of ERG. Fluorescence in situ hybridization (FISH) assessment demonstrated an unbalanced rearrangement of the EWSR1 gene. Further next-generation sequencing (NGS) analysis identified EWSR1-SMAD3 gene fusion. Molecular detection may be helpful for identifying new entities, in particular to those that lack lineage-specific differentiation by conventional pathological examinations.

H3K27 trimethylation loss in malignant peripheral nerve sheath tumor: a systematic review and meta-analysis with diagnostic implications

BACKGROUND

Multiple studies have reported the loss of trimethylation at lysine (K) 27 on histone 3 (H3K27me3) in high-grade malignant peripheral nerve sheath tumors (MPNSTs). However, the diagnostic potential of this finding in MPNSTs remains yet to be fully substantiated. Correspondingly, our aim was to pool systematically-identified metadata in the literature and substantiate the incidence of H3K27me3 loss in this setting.

METHODS

Searches of 7 electronic databases from inception to May 2019 were conducted following PRISMA guidelines. Articles were screened against pre-specified criteria. The incidence of loss was then pooled by random-effects meta-analysis of proportions.

RESULTS

Nine pertinent studies described a total of 823 high-grade MPNST samples. When pooled, incidence (sensitivity) of complete H3K27me3 loss was estimated to be 53% (95% CI 42-64%). For MPNST subtypes, estimated incidences of complete loss in NF1 subtype was 52% (95% CI 41-62), in sporadic subtype was 53% (95% CI 36-70%), in the epithelioid subtype was 0% (95% CI 0-7%), and radiation-associated subtype was 98% (95% CI 86-100%). Finally, incidence of incomplete loss (specificity) in 1231 MPNST-mimic samples was estimated to be 96% (95% CI 90-99%). Certainty of these outcomes ranged from very low to high.

CONCLUSIONS

The incidence of complete H3K27me3 loss is substantial in high-grade MPNSTs and is low in MPNST-mimics. Greater cohort study and biological investigation will validate the certainty of these findings as well as elucidate their true molecular and clinical significances.

H3K27 trimethylation loss in malignant peripheral nerve sheath tumor: a systematic review and meta-analysis with diagnostic implications

BACKGROUND

Multiple studies have reported the loss of trimethylation at lysine (K) 27 on histone 3 (H3K27me3) in high-grade malignant peripheral nerve sheath tumors (MPNSTs). However, the diagnostic potential of this finding in MPNSTs remains yet to be fully substantiated. Correspondingly, our aim was to pool systematically-identified metadata in the literature and substantiate the incidence of H3K27me3 loss in this setting.

METHODS

Searches of 7 electronic databases from inception to May 2019 were conducted following PRISMA guidelines. Articles were screened against pre-specified criteria. The incidence of loss was then pooled by random-effects meta-analysis of proportions.

RESULTS

Nine pertinent studies described a total of 823 high-grade MPNST samples. When pooled, incidence (sensitivity) of complete H3K27me3 loss was estimated to be 53% (95% CI 42-64%). For MPNST subtypes, estimated incidences of complete loss in NF1 subtype was 52% (95% CI 41-62), in sporadic subtype was 53% (95% CI 36-70%), in the epithelioid subtype was 0% (95% CI 0-7%), and radiation-associated subtype was 98% (95% CI 86-100%). Finally, incidence of incomplete loss (specificity) in 1231 MPNST-mimic samples was estimated to be 96% (95% CI 90-99%). Certainty of these outcomes ranged from very low to high.

CONCLUSIONS

The incidence of complete H3K27me3 loss is substantial in high-grade MPNSTs and is low in MPNST-mimics. Greater cohort study and biological investigation will validate the certainty of these findings as well as elucidate their true molecular and clinical significances.

Rhabdomyosarcoma arising from retroperitoneal teratoma in an infantile neurofibromatosis type 1 patient

We herein report the case of a 2-year-old girl with neurofibromatosis type 1 (NF1), who presented with a 12-cm mass in the right retroperitoneum and underwent tumor resection. Histologically, the tumor was composed of two distinct components: one was teratoma, showing mature morphology; and the other was embryonal rhabdomyosarcoma. An interphase fluorescence in situ hybridization (FISH) analysis of the rhabdomyosarcoma component revealed the absence of isochromosome 12p. Although it is well known that rhabdomyosarcoma occurs in infantile NF1, and that rhabdomyosarcoma can arise from teratoma as a somatic-type malignancy, to the best of our knowledge, this is the first case of an infantile NF1 patient, who developed rhabdomyosarcoma within a retroperitoneal teratoma. The absence of chromosome 12p alteration suggests a possibility that the rhabdomyosarcoma occurred due to the NF1 background, not as a somatic-type malignancy of germ cell tumor.

Uterine and vaginal sarcomas resembling fibrosarcoma: a clinicopathological and molecular analysis of 13 cases showing common NTRK-rearrangements and the description of a COL1A1-PDGFB fusion novel to uterine neoplasms

Mesenchymal neoplasms of the uterus (corpus and cervix) encompass a heterogeneous group of tumors with differing morphologies, immunophenotypes and molecular alterations. With the advent of modern molecular techniques, such as next generation sequencing, newly defined genetic abnormalities are being reported in this group of neoplasms. Herein we report the clinicopathological and molecular features of a series of 13 spindle cell sarcomas of the uterus and vagina (10 cervix, 2 uterine corpus, 1 vagina) with morphology resembling fibrosarcoma. After targeted RNA-sequencing, dual FISH fusion and array-CGH analysis, 7 of 13 tumors exhibited NTRK rearrangements (6 TPM3-NTRK1 and 1 EML4-NTRK3) and 3 a COL1A1-PDGFB fusion; in the other 3 neoplasms, all of which were positive with S100 (2 diffuse, 1 focal), we identified no rearrangement. All the NTRK fusion-positive sarcomas were located in the cervix and exhibited diffuse staining with Trk while all the other neoplasms were negative. CD34 was diffusely positive in all 3 of the COL1A1-PDGFB fusion sarcomas. The latter molecular abnormality is identical to that commonly found in dermatofibrosarcoma protuberans and has not been reported previously in uterine mesenchymal neoplasms. We suggest that uterine sarcomas with a morphology resembling fibrosarcoma (and in which leiomyosarcoma and the known molecularly confirmed high-grade endometrial stromal sarcomas have been excluded) can be divided into 3 groups:- an NTRK fusion group, a COL1A1-PDGFB fusion group and a group containing neither of these molecular abnormalities which, on the basis of positive staining with S100, could be tentatively classified as malignant peripheral nerve sheath tumor, although additional molecular studies may identify specific genetic alterations necessitating a nomenclature change. We suggest a diagnostic algorithm when reporting such neoplasms. Identification of these newly described fusion-associated sarcomas is important given the potential for targeted treatments.

Epigenetic Remodeling through Downregulation of Polycomb Repressive Complex 2 Mediates Chemotherapy Resistance in Testicular Germ Cell Tumors

A greater understanding of the hypersensitivity and curability of testicular germ cell tumors (TGCTs) has the potential to inform strategies to sensitize other solid tumors to conventional chemotherapies. The mechanisms of cisplatin hypersensitivity and resistance in embryonal carcinoma (EC), the stem cells of TGCTs, remain largely undefined. To study the mechanisms of cisplatin resistance we generated a large panel of independently derived, acquired resistant clones from three distinct parental EC models employing a protocol designed to match standard of care regimens of TGCT patients. Transcriptomics revealed highly significant expression changes shared between resistant cells regardless of their parental origin. This was dominated by a highly significant enrichment of genes normally repressed by H3K27 methylation and the polycomb repressive complex 2 (PRC2) which correlated with a substantial decrease in global H3K27me3, H2AK119 ubiquitination, and expression of BMI1. Importantly, repression of H3K27 methylation with the EZH2 inhibitor GSK-126 conferred cisplatin resistance to parental cells while induction of H3K27 methylation with the histone lysine demethylase inhibitor GSK-J4 resulted in increased cisplatin sensitivity to resistant cells. A gene signature based on H3K27me gene enrichment was associated with an increased rate of recurrent/progressive disease in testicular cancer patients. Our data indicates that repression of H3K27 methylation is a mechanism of cisplatin acquired resistance in TGCTs and that restoration of PRC2 complex function is a viable approach to overcome treatment failure.

H3K18Ac as a Marker of Cancer Progression and Potential Target of Anti-Cancer Therapy

Acetylation and deacetylation are posttranslational modifications (PTMs) which affect the regulation of chromatin structure and its remodeling. Acetylation of histone 3 at lysine placed on position 18 (H3K18Ac) plays an important role in driving progression of many types of cancer, including breast, colon, lung, hepatocellular, pancreatic, prostate, and thyroid cancer. The aim of this review is to analyze and discuss the newest findings regarding the role of H3K18Ac and acetylation of other histones in carcinogenesis. We summarize the level of H3K18Ac in different cancer cell lines and analyze its association with patients’ outcomes, including overall survival (OS), progression-free survival (PFS), and disease-free survival (DFS). Finally, we describe future perspectives of cancer therapeutic strategies based on H3K18 modifications.

Current Update on the Molecular Biology of Cutaneous Sarcoma: Dermatofibrosarcoma Protuberans

OPINION STATEMENT

Cutaneous sarcoma is a group of malignant mesenchymal tumors primarily involving the dermis, and it is characterized by extreme clinicopathological heterogeneity. Although its occurrence rate is rare, dermatofibrosarcoma protuberans (DFSP) is one of the most common types of dermal sarcoma. DFSP grows slowly and tends to relapse locally after inadequate resection. There are various histological variants of DFSP tumors and it often mimics benign lesions such as dermatofibroma and scar, which make accurate diagnosis difficult and delayed, and some cases progress to the stage where the tumor is unresectable. Recent advancements in cancer genetics and molecular biology methods have elucidated the COL1A1-PDGFB fusion gene, some novel fusion gene variants and pathways related to DFSP pathogenesis that have resulted in the evolution of cutaneous sarcoma diagnosis and treatment. For example, some clinical studies have confirmed the efficacy of imatinib methylate, an αPDGFR-targeted therapy for unresectable or metastatic DFSP. The present review summarizes recent updates in DFSP research, diagnostics, and treatment.