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Activating RAS mutations are found in a subset of fusion-negative rhabdomyosarcoma (RMS), and therapeutic strategies to directly target RAS in these tumors have been investigated, without clinical success to date. A potential strategy to inhibit oncogenic RAS activity is the disruption of RAS prenylation, an obligate step for RAS membrane localization and effector pathway signaling, through inhibition of farnesyltransferase (FTase). Of the major RAS family members, HRAS is uniquely dependent on FTase for prenylation, whereas NRAS and KRAS can utilize geranylgeranyl transferase as a bypass prenylation mechanism. Tumors driven by oncogenic HRAS may therefore be uniquely sensitive to FTase inhibition. To investigate the mutation-specific effects of FTase inhibition in RMS we utilized tipifarnib, a potent and selective FTase inhibitor, in in vitro and in vivo models of RMS genomically characterized for RAS mutation status. Tipifarnib reduced HRAS processing, and plasma membrane localization leading to decreased GTP-bound HRAS and decreased signaling through RAS effector pathways. In HRAS-mutant cell lines, tipifarnib reduced two-dimensional and three-dimensional cell growth, and in vivo treatment with tipifarnib resulted in tumor growth inhibition exclusively in HRAS-mutant RMS xenografts. Our data suggest that small molecule inhibition of FTase is active in HRAS-driven RMS and may represent an effective therapeutic strategy for a genomically-defined subset of RMS patients.

Subsets of high-grade gliomas, including glioblastoma (GBM), are known to utilize the alternative lengthening of telomeres (ALT) pathway for telomere length maintenance. However, the telomere maintenance profile of one subtype of GBM—giant cell GBM—has not been extensively studied. Here, we investigated the prevalence of ALT, as well as ATRX and SMARCAL1 protein loss, in a cohort of classic giant cell GBM and GBM with giant cell features. To determine the presence of ALT, a telomere-specific fluorescence in situ hybridization assay was performed on 15 cases of classic giant cell GBM, 28 additional GBMs found to have giant cell features, and 1 anaplastic astrocytoma with giant cell features. ATRX, SMARCAL1, and IDH1 protein status were assessed in a proportion of cases by immunohistochemistry and were compared to clinical-pathologic and molecular characteristics. In the overall cohort of 44 cases, 19 (43%) showed evidence of ALT. Intriguingly, of the ALT-positive cases, only 9 (47.4%) displayed loss of the ALT suppressor ATRX by immunohistochemistry. Since inactivating mutations in SMARCAL1have been identified in ATRX wild-type ALT-positive gliomas, we developed an immunohistochemistry assay for SMARCAL1 protein expression using genetically validated controls. Of the 19 ALT-positive cases, 6 (31.5%) showed loss or mis-localization of SMARCAL1 by immunohistochemistry. Of these cases, four retained ATRX protein expression, while two cases also displayed ATRX loss. Additionally, we assessed five cases from which multiple temporal samples were available and ALT status was concordant between both tumor biopsies. In summary, we have identified a subset of giant cell GBM that utilize the ALT telomere maintenance mechanism. Importantly, in addition to ATRX loss, ALT-positive tumors harboring SMARCAL1 alterations are prevalent in giant cell GBM.

Neoplasms of the peripheral nervous system represent a heterogenous group with a wide spectrum of morphological features and biological potential. They range from benign and curable by complete excision (schwannoma and soft tissue perineurioma) to benign but potentially aggressive at the local level (plexiform neurofibroma) to the highly malignant (malignant peripheral nerve sheath tumors [MPNST]). In this review, we discuss the diagnostic and pathologic features of common peripheral nerve sheath tumors, particularly those that may be encountered in the intracranial compartment or in the spine and paraspinal region. The discussion will cover schwannoma, neurofibroma, atypical neurofibromatous neoplasms of uncertain biological potential, intraneural and soft tissue perineurioma, hybrid nerve sheath tumors, MPNST, and the recently renamed enigmatic tumor, malignant melanotic nerve sheath tumor, formerly referred to as melanotic schwannoma. We also discuss the diagnostic relevance of these neoplasms to specific genetic and familial syndromes of nerve, including neurofibromatosis 1, neurofibromatosis 2, and schwannomatosis. In addition, we discuss updates in our understanding of the molecular alterations that represent key drivers of these neoplasms, including neurofibromatosis type 1 and type 2, SMARCB1, LZTR1, and PRKAR1Aloss, as well as the acquisition of CDKN2A/Bmutations and alterations in the polycomb repressor complex members (SUZ12and EED) in the malignant progression to MPNST. In summary, this review covers practical aspects of pathologic diagnosis with updates relevant to neurosurgical practice.

Glioma-associated oncogene homolog 3 (GLI3), whose main function is to inhibit GLI1, has been associated with neuronal differentiation in medulloblastoma. However, it is not clear what molecular subtype(s) show increased GLI3 expression. GLI3 levels were assessed by immunohistochemistry in 2 independent cohorts, including a total of 88 cases, and found to be high in both WNT- and SHH-activated medulloblastoma. Analysis of bulk mRNA expression data and single cell RNA sequencing studies confirmed that GLI1and GLI3are highly expressed in SHH-activated medulloblastoma, whereas GLI3but not GLI1is highly expressed in WNT-activated medulloblastoma. Immunohistochemical analysis has shown that GLI3 is expressed inside the neuronal differentiated nodules of SHH-activated medulloblastoma, whereas GLI1/2 are expressed in desmoplastic areas. In contrast, GLI3 is diffusely expressed in WNT-activated medulloblastoma, whereas GLI1 is suppressed. Our data suggest that GLI3 may be a master regulator of neuronal differentiation and morphology in these subgroups.

Mutations in histone H3 are key molecular drivers of pediatric and young adult high-grade gliomas. Histone H3 G34R mutations occur in hemispheric high-grade gliomas and H3 K27M mutations occur in aggressive, though histologically diverse, midline gliomas. Here, we report 2 rare cases of histologically low-grade gliomas with gemistocytic morphology and sequencing-confirmed histone H3 G34R mutations. One case is a histologically low-grade gemistocytic astrocytoma with a G34R-mutation in H3F3A. The second case is a histologically low-grade gemistocytic astrocytoma with co-occurring K27M and G34R mutations in HIST1H3B. Review of prior histone H3-mutant gliomas sequenced at our institution shows a divergent clinical and immunohistochemical pattern in the 2 cases. The first case is similar to prior histone H3 G34R-mutant tumors, while the second case most closely resembles prior histone H3 K27M-mutant gliomas. These represent novel cases of sequencing-confirmed histone H3 G34R-mutant gliomas with low-grade histology and add to the known rare cases of G34R-mutant tumors with gemistocytic morphology. Although K27M and G34R mutations are thought to be mutually exclusive, we document combined K27M and G34R mutations in HIST1H3B and present evidence suggesting the K27M-mutation drove tumor phenotype in this dual mutant glioma.

Telomeres are nucleoprotein complexes located at the termini of eukaryotic chromosomes that prevent exonucleolytic degradation and end-to-end chromosomal fusions. Cancers often have critically shortened, dysfunctional telomeres contributing to genomic instability. Telomere shortening has been reported in a wide range of precancerous lesions and invasive carcinomas. However, the role of telomere alterations, including the presence of alternative lengthening of telomeres (ALT), has not been studied in pituitary adenomas. Telomere length and the presence of ALT were assessed directly at the single cell level using a telomere-specific fluorescence in situ hybridization assay in tissue microarrays. Tumors were characterized as either ALT-positive or having short, normal, or long telomere lengths and then these categories were compared with clinicopathological characteristics. ATRX and DAXX expression was studied through immunohistochemistry. We characterized a discovery set of 106 pituitary adenomas including both functional and nonfunctional subsets (88 primary, 18 recurrent). Telomere lengths were estimated and we observed 64 (59.4%) cases with short, 39 (36.8%) cases with normal, and 0 (0%) cases with long telomeres. We did not observe significant differences in the clinicopathological characteristics of the group with abnormally shortened telomeres compared to the group with normal telomeres. However, three pituitary adenomas were identified as ALT-positive of which two were recurrent tumors. Two of these three ALT-positive cases had alterations in either of the chromatin remodeling proteins, ATRX and DAXX, which are routinely altered in other ALT-positive tumor subtypes. In a second cohort of 32 recurrent pituitary adenomas from 22 patients, we found that the tumors from 36% of patients (n= 8) were ALT-positive. This study demonstrates that short telomere lengths are prevalent in pituitary adenomas and that ALT-positive pituitary adenomas are enriched in recurrent disease.

Neurogenic tumors represent a broad ill-defined category of neoplasms that includes tumors of Schwann cell and/or neuroblastic derivation, as well as neoplasms that typically develop in the central nervous system, but rarely present in ectopic sites including the mediastinum. Neurogenic tumors may occur at many different anatomic sites, but the mediastinum represents a uniquely challenging site given the complex anatomy. Additionally, some of these neoplasms may present with multicentric involvement in the context of genetic syndromes, including NF1, NF2 and schwanomatosis. Most of these develop in posterior structures, often in association with paraspinal structures. Fine needle biopsy/small biopsies play an important role in the diagnosis of these neoplasms, given its record of safety and the increased applicability of ancillary testing to these smaller samples at the present time. In this review we focus on the major categories of neurogenic tumors that may be encountered in the mediastinum, including schwannoma, neurofibroma, malignant peripheral nerve sheath tumors, ganglioneuroma and ganglioneuroblastoma, as well as rarer members of this category. We discuss diagnostic approaches applicable to small cytologic and tissue samples and relevant differential diagnoses.

Localized hypertrophic neuropathy is a rare Schwann cell proliferation that usually affects single nerves from the extremities, and it is of unclear etiology in its pure form. RASopathies are a defined group of genetic diseases with overlapping clinical features, usually secondary to germline mutations in genes encoding either components or regulators of the RAS/MAPK pathway. Herein, we report an 11-year-old boy presenting with café au lait spots and right leg length discrepancy. A fascicular nerve biopsy of the tibial nerve demonstrated a Schwann cell proliferation with prominent onion-bulb formation, satisfying criteria for localized hypertrophic neuropathy. Molecular genetic analysis demonstrated identical KRASmutations (c38_40dupGCG) in the peripheral nerve lesion and melanocytes from café au lait spots, but not in blood, supporting a diagnosis of a KRAS-mediated rasopathy with mosaicism. Immunohistochemical staining in the peripheral nerve lesion demonstrated strong pERK staining consistent with downstream MAPK pathway activation. This report suggests that at least a subset of localized hypertrophic neuropathies are bonafide, well-differentiated Schwann cell neoplasms developing through oncogenic RAS signaling, which provides new insights into the controversial entity historically known as localized hypertrophic neuropathy.

Neuronal/mixed glioneuronal tumors are central nervous system neoplasms composed of neoplastic neuronal cell components or a mixture of glial and neuronal elements. They occur in cerebral hemispheres, posterior fossa, and spinal cord. Compared with other tumors at these locations, diencephalic neuronal/glioneuronal tumors are very rare and therefore not well characterized. We hereby performed clinicopathologic evaluation on 10 neuronal/glioneuronal tumors arising from the diencephalic region. Morphologically, these tumors resemble their histologic counterparts in other locations, except that lymphocytic infiltrates and microcalcifications are more common than Rosenthal fibers or eosinophilic granular bodies. The BRAFV600 mutation rate is 75%. Given the high percentage of samples being small biopsy specimens, the subtle histologic features and molecular findings greatly aided in establishing the pathologic diagnosis in several cases. At a median follow-up of 42 months, 71% of the tumors demonstrated radiological recurrence or progression, with median progression-free survival of 18 months. Recurrence/progression is observed in tumors across different histologic subtypes, necessitating additional therapies in 56% of the cases. Despite their bland histology, diencephalic neuronal/glioneuronal tumors are not clinically indolent. Their frequent recurrences warrant a close follow-up, and the prevalent BRAF mutation makes MAPK pathway inhibition a plausible treatment option when conventional therapies fail.

Nervous system tumors, particularly brain tumors, represent the most common tumors in children and one of the most lethal tumors in adults. Despite decades of research, there are few effective therapies for these cancers. Although human nervous system tumor cells and genetically engineered mouse models have served as excellent platforms for drug discovery and preclinical testing, they have limitations with respect to accurately recapitulating important aspects of the pathobiology of spontaneously arising human tumors. For this reason, attention has turned to the deployment of human stem cell engineering involving human embryonic or induced pluripotent stem cells, in which genetic alterations associated with nervous system cancers can be introduced. These stem cells can be used to create self-assembling three-dimensional cerebral organoids that preserve key features of the developing human brain. Moreover, stem cell-engineered lines are amenable to xenotransplantation into mice as a platform to investigate the tumor cell of origin, discover cancer evolutionary trajectories and identify therapeutic vulnerabilities. In this article, we review the current state of human stem cell models of nervous system tumors, discuss their advantages and disadvantages, and provide consensus recommendations for future research.

Pineal parenchymal tumors are rare neoplasms, ranging from WHO Grade I to IV. There are few studies characterizing the molecular profiles of these tumors. ATRXalterations are strongly associated with the presence of the alternative lengthening of telomeres (ALT) phenotype, and within the central nervous system they tend to occur in subsets of gliomas, including those with IDH, NF1, or histone(H3 K27M or G34) mutations. Here, we identified ATRXframeshift mutations by next generation sequencing associated with corresponding protein loss in 2 cases of pineal parenchymal tumors of intermediate differentiation (PPTID) developing in a 21-year-old woman and a 64-year-old man. In contrast, we identified partial ATRX loss in 1 pineoblastoma, among 14 pineal parenchymal tumors of various grades (6 pineoblastomas, 4 pineocytomas, and 4 PPTID) using tissue microarrays; ALT was absent in these cases. Evaluating the cBioPortal database, an ATRXmutation was identified in one (of 3 total) PPTIDs analyzed. Thus, ATRXmutations associated with protein loss and ALT develop in a small subset of pineal parenchymal tumors and may be limited to those with intermediate differentiation. The clinical significance of these alterations requires further study.

Neurocytoma (NC) is a rare, low-grade tumor of the central nervous system, with a 10-year survival rate of 90% and local control rate of 74%. However, 25% of NCs will be atypical, with an elevated Ki-67 labeling index >2%, and will exhibit a more aggressive course, with a high propensity for local recurrence and/or craniospinal dissemination. Although no standard treatment regimen exists for these atypical cases, adjuvant stereotactic or conventional radiotherapy and/or chemotherapy have been typically offered but have yielded inconsistent results.

Overgrowth of neuroglial tissue is rare in testicular germ cell tumors and mostly reported as isolated cases. We retrospectively reviewed 13 cases of testicular germ cell tumors from 2 institutions from 1995 to 2018. Hematoxylin and eosin slides were collected and reviewed. Immunohistochemistry was performed in all cases with available material. The series included 4 primary tumors and 9 metastases, including 8 retroperitoneal and 1 axillary lymph node (LN). The average age was 34 (range: 19 to 54). Five of the LN dissections were postchemotherapy, with one a recurrence 5 years after the initial diagnosis. The average tumor size for primary tumors was 5.15 cm (range: 1.7 to 7.3) and for metastases was 6.4 cm (range: 0.6 to 15). The largest size of the neuroglial component was 4.5 cm in the primary tumors and 7.5 cm in metastatic sites. The neuroglial component in the primary site was associated with pure teratoma (n=2) and with a mixed germ cell tumor (teratoma, seminoma, and embryonal carcinoma) (n=2). Cases involving LNs were associated with teratoma (n=4), seminoma (n=2), rhabdomyosarcoma (n=2), primitive neuroectodermal tumors (n=1), and high-grade sarcoma (n=1) (some with >1 other component). Two cases were pure glial tumor. Histologically, the neuroglial components included low-grade astrocytoma (n=3) (both with microcysts formation and pilocytic features), gemistocytic astrocytomas (n=3), anaplastic astrocytoma (n=2), ganglioglioma (n=1), glioblastoma (n=2), gliosarcoma (n=1), and developing central nervous system (CNS) (n=2). By immunohistochemistry, 13/13 (100%) cases were GFAP(+), 10/10 (100%) cases showed retained ATRX, 10/10 were IDH1 pR132H (−), 5/10 (50%) were p53 (+). A single case 1/10 (10%) was BRAF p.V600E (+), but a mutation was not identified by polymerase chain reaction. Follow-up was available in 6 patients; 4 were confirmed to have received chemotherapy with BEP; 1 had a local recurrence and the patient with gliosarcoma developed a lung metastasis morphologically similar to the gliosarcoma of the retroperitoneum. In conclusion, neuroglial differentiation and neoplasms are rare in testicular germ cell tumors and are most commonly associated with teratomas; they can be seen in primary and metastatic sites. They exhibit the full range of neuroglial differentiation including developing CNS to gliomas/glioneuronal tumors WHO grades I-IV. None of the cases showed results consistent with ATRX, IDHor BRAFalterations, suggesting they have different oncogenic mechanisms than their CNS counterparts.

The genetic alterations that define primary central nervous system lymphoma (PCNSL) are incompletely elucidated, and the genomic evolution from diagnosis to relapse is poorly understood. We performed whole-exome sequencing (WES) on 36 PCNSL patients and targeted MYD88 sequencing on a validation cohort of 27 PCNSL patients. We also performed WES and phylogenetic analysis of 3 matched newly diagnosed and relapsed tumor specimens and 1 synchronous intracranial and extracranial relapse. Immunohistochemistry (IHC) for programmed death-1 ligand (PD-L1) was performed on 43 patient specimens. Combined WES and targeted sequencing identified MYD88 mutation in 67% (42 of 63) of patients, CDKN2A biallelic loss in 44% (16 of 36), and CD79b mutation in 61% (22 of 36). Copy-number analysis demonstrated frequent regions of copy loss (ie, CDKN2A), with few areas of amplification. CD79b mutations were associated with improved progression-free and overall survival. We did not identify amplification at the PD-1/PD-L1 loci. IHC for PD-L1 revealed membranous expression in 30% (13 of 43) of specimens. Phylogenetic analysis of paired primary and relapsed specimens identified MYD88 mutation and CDKN2A loss as early clonal events. PCNSL is characterized by frequent mutations within the B-cell receptor and NF-κB pathways. The lack of PD-L1 amplifications, along with membranous PD-L1 expression in 30% of our cohort, suggests that PD-1/PD-L1 inhibitors may be useful in a subset of PCNSL. WES of PCNSL provides insight into the genomic landscape and evolution of this rare lymphoma subtype and potentially informs more rational treatment decisions.

The genetic alterations that define primary central nervous system lymphoma (PCNSL) are incompletely elucidated, and the genomic evolution from diagnosis to relapse is poorly understood. We performed whole-exome sequencing (WES) on 36 PCNSL patients and targeted MYD88sequencing on a validation cohort of 27 PCNSL patients. We also performed WES and phylogenetic analysis of 3 matched newly diagnosed and relapsed tumor specimens and 1 synchronous intracranial and extracranial relapse. Immunohistochemistry (IHC) for programmed death-1 ligand (PD-L1) was performed on 43 patient specimens. Combined WES and targeted sequencing identified MYD88mutation in 67% (42 of 63) of patients, CDKN2Abiallelic loss in 44% (16 of 36), and CD79bmutation in 61% (22 of 36). Copy-number analysis demonstrated frequent regions of copy loss (ie, CDKN2A), with few areas of amplification. CD79bmutations were associated with improved progression-free and overall survival. We did not identify amplification at the PD-1/PD-L1loci. IHC for PD-L1 revealed membranous expression in 30% (13 of 43) of specimens. Phylogenetic analysis of paired primary and relapsed specimens identified MYD88mutation and CDKN2Aloss as early clonal events. PCNSL is characterized by frequent mutations within the B-cell receptor and NF-κB pathways. The lack of PD-L1amplifications, along with membranous PD-L1 expression in 30% of our cohort, suggests that PD-1/PD-L1 inhibitors may be useful in a subset of PCNSL. WES of PCNSL provides insight into the genomic landscape and evolution of this rare lymphoma subtype and potentially informs more rational treatment decisions.

Neurofibromatosis type-1 is a familial genetic syndrome associated with a predisposition to develop peripheral and central nervous system neoplasms. We have previously reported on a subset of gliomas developing in these patients with morphologic features resembling subependymal giant cell astrocytoma, but the molecular features of these tumors remain undefined. A total of 14 tumors were studied and all available slides were reviewed. Immunohistochemical stains and telomere-specific FISH were performed on all cases. In addition, next-generation sequencing was performed on 11 cases using a platform targeting 644 cancer-related genes. The average age at diagnosis was 28 years (range: 4–60, 9F/5M). All tumors involved the supratentorial compartment. Tumors were predominantly low grade (n= 12), with two high-grade tumors, and displayed consistent expression of glial markers. Next-generation sequencing demonstrated inactivating NF1mutations in 10 (of 11) cases. Concurrent TSC2and RPTORmutations were present in two cases (1 sporadic and 1 neurofibromatosis type-1-associated). Interestingly, alternative lengthening of telomeres was present in 4 (of 14) (29%) cases. However, an ATRXmutation associated with aberrant nuclear ATRX expression was identified in only one (of four) cases with alternative lenghtening of telomeres. Gene variants in the DNA helicase RECQL4(n= 2) and components of the Fanconi anemia complementation group (FANCD2, FANCF, FANCG)(n= 1) were identified in two alternative lenghtening of telomere-positive/ATRX-intact cases. Other variants involved genes related to NOTCH signaling, DNA maintenance/repair pathways, and epigenetic modulators. There were no mutations identified in DAXX, PTEN, PIK3Cgenes, TP53, H3F3A, HIST1H3B, or in canonical hotspots of IDH1, IDH2, or BRAF. A subset of subependymal giant cell astrocytoma-like astrocytomas are alternative lenghtening of telomere-positive and occur in the absence of ATRX alterations, thereby suggesting mutations in other DNA repair/maintenance genes may also facilitate alternative lenghtening of telomeres. These findings suggest that subependymal giant cell astrocytoma-like astrocytoma represents a biologically distinct group that merits further investigation.

Supplemental Digital Content is available in the text.Central nervous system (CNS)-type tumors and tumor-like proliferations arising in the gynecologic tract and pelvis are rare. Clinicopathologic features of 23 cases are reported using the current WHO classification system for CNS tumors, with selected relevant immunohistochemical and molecular genetic analyses when possible. There were 12 embryonal tumors, including 7 medulloepitheliomas, 2 embryonal tumors (not otherwise specified), 1 embryonal tumor with multilayered rosettes, 1 embryonal tumor with features of nodular desmoplastic medulloblastoma, and 1 medulloblastoma with extensive nodularity, with primary sites including ovary (7), uterus/endometrium (3), and pelvis (2). Six ovarian tumors had associated germ cell tumors (3 immature teratomas [1 also with yolk sac tumor], 2 mature cystic teratomas, and 1 yolk sac tumor). These tumors typically had some expression of synaptophysin (10/10), GFAP (5/9), S100 (3/6), and NeuN (3/3) and were negative for C19MC amplicon by fluorescence in situ hybridization (0/5). There were 6 glial tumors, including 3 ependymomas (1 anaplastic), 1 oligodendroglioma, not otherwise specified, 1 pilocytic astrocytoma, and 1 atypical glial proliferation after therapy of a high-grade high-stage immature teratoma, with primary sites including ovary (4), fallopian tube (1), and pelvic sidewall (1). Four ovarian tumors had associated teratomas (2 immature and 2 mature). These tumors expressed GFAP (5/6), OLIG2 (2/3), and S100 (1/1), and the pilocytic astrocytoma was negative for BRAF (V600E) mutant protein. There were 4 neuronal or mixed glioneuronal tumors, including 3 neurocytomas and 1 malignant (high-grade) glioneuronal neoplasm, all primary ovarian and associated with teratomas (3 mature, 1 immature). These tumors expressed synaptophysin (4/4), GFAP (1/3), NeuN (1/2), and OLIG2 (1/2). Single-nucleotide polymorphism microarray analysis of the malignant glioneuronal neoplasm demonstrated a partial deletion at location (1)(p36.23p35.2) on chromosome 1p, and 2 regions of deletion at locations (19)(q11q13.12) and (19)(q13.41qter) on 19q. One neurocytoma had no 1p and 19q co-deletions. There was 1 meningioma in the pelvis. For 10 patients with embryonal tumors and follow-up, 5 were alive with no evidence of disease (mean/median: 60/52 mo), 4 were alive with recurrent disease (mean/median: 32/31 mo), and 1 died of disease (13 mo). For 5 patients with other tumor types and follow-up, all were alive without evidence of disease (mean/median: 33/30 mo). Diagnostic evaluation and classification per systems used for primary CNS tumors are recommended for the wide spectrum of CNS-type neuroepithelial tumors that can occur in the female genital tract and pelvis.

Malignant peripheral nerve sheath tumors (MPNST) are aggressive spindle cell neoplasms that may occur sporadically, often in association with radiation exposure, or in the clinical context of Neurofibromatosis type 1. MPNST are known to harbor genetic alterations affecting the function of polycomb repressive complex 2 (PRC2), resulting in profound changes to global H3K27me3 levels. Recent evidence suggests a link between the polycomb complex and DNA methylation. Given the established epigenetic alterations found in MPNST, we aimed to further explore global methylation changes including 5-methylcystosine (5mC), 5-hydroxymethylcytosine (5hmC), and H3K27me3 levels using previously validated immunolabeling protocols in a representative cohort of 28 peripheral nerve sheath tumors (MPNST [n = 8], localized cutaneous neurofibroma [n = 10], and plexiform neurofibroma [n = 10]). MPNST showed significantly decreased levels of H3K27me3 (p < 0.0002) and 5mC (p = 0.0001) with levels of 5hmC showing borderline statistical significance (p = 0.05) when compared to localized and plexiform neurofibromas. Immunohistochemical findings of decreased H3K27me3 and 5mC further our understanding of global epigenetic alterations observable in MPNST and may provide insight into the basis of tumor progression as well as prognostic and treatment implications in the future.

Intracranial chondromas are rare tumors, especially in the pediatric population. We describe the conventional and advanced neuroimaging characteristics of this rare convexity dura-based chondroma in a young adolescent. In particular we demonstrate that diffusion-weighted imaging (DWI) facilitates differentiation between a dura-based chondroma and the more frequent classical meningioma. Chondromas are typically DWI hypointense with high apparent diffusion coefficient (ADC) values while meningiomas are typically DWI hyperintense with low ADC values. We also discuss the relevant additional differential diagnoses of dura based focal lesions for the pediatric population as well as the diagnostic significance of additional imaging modalities, including computed tomography, magnetic resonance imaging and cerebral angiography.

Social media use continues to grow among pathologists. Discussions of current topics, posts of educational information, and images of pathological entities are commonly found and distributed on popular sites such as Facebook and Twitter. However, little is known about the presence of neuropathology content in social media and the audience for such content. We designed and distributed a survey to assess the demographics of users viewing neuropathology content and their opinions about neuropathology in social media. User posts on the Facebook group, Surgical Neuropathology, were also analyzed. The results show that there is a demand for neuropathology content of high quality, curated by experts, and that this demand is present among both specialists and nonspecialists. These findings suggest that social media may be useful for rapid dissemination of information in the field of neuropathology. This format also offers a unique opportunity to extend the reach of information to nonneuropathologists who may not receive neuropathology journals or have access to specialty-level neuropathology training, to build networks between professionals, and potentially to influence public opinion of neuropathology on an international scale.

Tumors with a neuronal component comprise a small percentage of central nervous system (CNS) neoplasms overall, but the presence of neuronal differentiation has important diagnostic, prognostic, and therapeutic implications. Insulinoma-associated protein 1 (INSM1) is a transcription factor with strong nuclear immunostaining in neuroendocrine cells and neoplasms of neuroendocrine origin; however, its expression in the CNS in normal brain and in neoplastic cells has not been fully explored. Here, we present immunostaining results from a large number of archival CNS tissue specimens, including 416 tumors. Nuclear immunostaining for INSM1 was frequently seen in medulloblastomas (87%, n = 94). Diffuse nuclear INSM1 immunostaining was detected in all central neurocytomas and pituitary adenomas. Patchy to rare staining with INSM1 was also seen in other high-grade embryonal tumors and high-grade gliomas. In normal brain tissue, specific nuclear INSM1 immunohistochemical staining was only seen in early neuronal development. Notably, nuclear INSM1 staining was not seen in adult normal brain, including areas of gliosis. These findings indicate that nuclear INSM1 immunostaining may serve as a strong nuclear marker in the brain for neoplasms of neuroendocrine or immature neuronal differentiation, when used in concert with other immunostains.

Accurate pathological diagnosis is crucial for optimal management of patients with cancer. For the approximately 100 known tumour types of the central nervous system, standardization of the diagnostic process has been shown to be particularly challenging—with substantial inter-observer variability in the histopathological diagnosis of many tumour types. Here we present a comprehensive approach for the DNA methylation-based classification of central nervous system tumours across all entities and age groups, and demonstrate its application in a routine diagnostic setting. We show that the availability of this method may have a substantial impact on diagnostic precision compared to standard methods, resulting in a change of diagnosis in up to 12% of prospective cases. For broader accessibility, we have designed a free online classifier tool, the use of which does not require any additional onsite data processing. Our results provide a blueprint for the generation of machine-learning-based tumour classifiers across other cancer entities, with the potential to fundamentally transform tumour pathology.

A 59-year-old woman with a remote history of invasive ductal carcinoma of the breast was found on a follow-up computed tomography scan of her brain to have a 1-cm lesion in the right frontal lobe in 2008. In the ensuing years, before her current admission, multiple imaging studies of the brain revealed that the lesion was stable and it was, therefore, interpreted as a small area of encephalomalacia related to a thrombosed cortical vein, a cavernoma, or treated metastatic breast cancer. In 2013, the patient underwent a bilateral salpingo-oophorectomy for ovarian tumors that were diagnosed as bilateral serous cystadenofibromas. A partial omentectomy showed no evidence of implants. In June 2016, the brain lesion was completely excised and diagnosed as an atypical proliferative (borderline) serous tumor. Immunohistochemical staining demonstrated that the tumor cells were immunoreactive for Pax8, WT-1, ER, and CK-7 and negative for Gata-3, PR, TTF-1, CDX-2, Napsin A, and CK-20, which was consistent with that diagnosis. We present a brief review of possible mechanisms to account for this unusual presentation and speculate that the most likely one is exfoliation of fallopian tube epithelial cells into the peritoneal cavity, which then gain access to lymphatics resulting in cells implanting in the brain and subsequently progressing to an atypical proliferative (borderline) serous tumor.

Background/Aims:Hemophagocytic lymphohistiocytosis (HLH) is an infrequent inflammatory multisystemic syndrome. Only rare cases with ophthalmic involvement describing their pathologic features have been previously reported. Methods:We report 3 cases of adult-onset HLH with bilateral ocular involvement and describe their clinicopathologic features. Results:Three adult males - 2 with a history of viral infection - developed persistent fever, fatigue, bone marrow abnormalities, and irreversible multiorgan failure. Visual impairment was also documented in 2 cases. Complete autopsies were performed. Ophthalmic pathology demonstrated a bilateral histiocytic infiltrate with scant lymphocytes affecting the uvea. Focal extension to the retina, optic nerve, and trabecular meshwork were also identified, as well as hemophagocytosis in 1 case. Macrophages showed strong immunoreactivity for CD163 antibody and lacked BRAF p.V600E mutant protein. Conclusion:HLH is an unusual disorder associated with several systemic conditions. Histologic features in the eye are poorly documented, with prior reports restricted to children. Our 3 adult cases are reported using updated criteria and, despite the difference in age, show changes similar to those observed in the pediatric population.

In recent years, an increasing role for noncoding small RNAs (miRNA) has been uncovered in carcinogenesis. These oligonucleotides can promote degradation and/or inhibit translation of key mRNAs. Recent studies have also highlighted a possible role for miRNAs in adult and pediatric brain tumors, including high- and low-grade gliomas, medulloblastoma, ependymoma, and neoplasms associated with neurofibromatosis type 1. Gliomas represent the most common category of primary intraparenchymal brain tumors, and, for example, manipulation of signaling pathways, through inhibition of PTEN transcription appears to be an important function of miRNA dysregulation through miR-21, miR-106b, and miR-26a. Moreover, altered miRNA expression in gliomas play roles in the regulation of common tumorigenic processes, including receptor tyrosine kinase signaling, angiogenesis, invasion, suppression of differentiation, cell cycle enhancement, and inhibition of apoptosis. Suppression of differentiation requires the downregulation of a number of miRNAs that are both enriched in the brain and required for terminal glial differentiation, including miR-219 and miR-338. Our evolving understanding about the biology of gliomas make them attractive for miRNA study, given that recent evidence suggests that epigenetic and subtle genetic changes may contribute to their pathogenesis. Identification of key miRNAs also provides a rationale for developing robust biomarkers and inhibitory RNA strategies for therapeutic purposes in glioma patients.

Low-grade (WHO I-II) gliomas and glioneuronal tumors represent the most frequent primary tumors of the central nervous system in children. They often have a good prognosis following total resection, however they can create many neurological complications due to mass effect, and may be difficult to resect depending on anatomic location. MicroRNAs have been identified as molecular regulators of protein expression/translation that can repress multiple mRNAs concurrently through base pairing, and have an important role in cancer, including brain tumors. Using the NanoString digital counting system, we analyzed the expression levels of 800 microRNAs in nine low-grade glial and glioneuronal tumor types (n=45). A set of 61 of these microRNAs were differentially expressed in tumors compared with the brain, and several showed levels varying by tumor type. The expression differences were more accentuated in subependymal giant cell astrocytoma, compared with other groups, and demonstrated the highest degree of microRNA repression validated by RT-PCR, including miR-129-2-3p, miR-219-5p, miR-338-3p, miR-487b, miR-885-5p, and miR-323a-3p. Conversely, miR-4488 and miR-1246 were overexpressed in dysembryoplastic neuroepithelial tumors compared with the brain and other tumors. The cluster 14q32.31 member miR-487b was variably under-expressed in pediatric glioma lines compared with human neural stem cells. Overexpression of miR-487b in a pediatric glioma cell line (KNS42) using lentiviral vectors led to a decrease in colony formation in soft agar (30%) (P<0.05), and decreased expression of known predicted targets PROM1 and Nestin (but not WNT5A). miR-487b overexpression had no significant effect on cell growth, proliferation, sensitivity to temozolomide, migration, or invasion. In summary, microRNA regulation appears to have a role in the biology of glial and glioneuronal tumor subtypes, a finding that deserves further investigation.

Cilia are highly conserved organelles, which serve critical roles in development and physiology. Motile cilia are expressed in a limited range of tissues, where they principally regulate local extracellular fluid dynamics. In contrast, primary cilia are expressed by many vertebrate cell types during interphase, and are intimately involved in the cell cycle and signal transduction. Notably, primary cilia are essential for vertebrate hedgehog pathway activity. Improved detection of motile cilia may assist in the diagnosis of some pathologic entities such as Rathke’s cleft cysts, whereas characterizing primary cilia in neoplastic tissues may implicate cilia-dependent signaling pathways as critical for tumorigenesis. We show that immunohistochemistry for the nuclear transcription factor FOXJ1, a master regulator of motile ciliogenesis, robustly labels the motile ciliated epithelium of Rathke's cleft cysts. FOXJ1 expression discriminates Rathke's cleft cysts from entities in the sellar/suprasellar region with overlapping histologic features such as craniopharyngiomas. Co-immunohistochemistry for FOXJ1 and markers that highlight motile cilia such as acetylated tubulin (TUBA4A) and the small GTPase ARL13B further enhance the ability to identify diagnostic epithelial cells. In addition to highlighting motile cilia, ARL13B immunohistochemistry also robustly highlights primary cilia in formalin-fixed paraffin-embedded sections. Primary cilia are present throughout the neoplastic epithelium of adamantinomatous craniopharyngioma, but are limited to basally oriented cells near the fibrovascular stroma in papillary craniopharyngioma. Consistent with this differing pattern of primary ciliation, adamantinomatous craniopharyngiomas express significantly higher levels of SHH, and downstream targets such as PTCH1 and GLI2, compared with papillary craniopharyngiomas. In conclusion, motile ciliated epithelium can be readily identified using immunohistochemistry for FOXJ1, TUBA4A, and ARL13B, facilitating the diagnosis of Rathke’s cleft cysts. Primary cilia can be identified by ARL13B immunohistochemistry in routine pathology specimens. The widespread presence of primary cilia in adamantinomatous craniopharyngioma implicates cilia-dependent hedgehog signaling in the pathogenesis of adamantinomatous craniopharyngioma.

Gliomas represent the most common primary intraparenchymal tumors of the central nervous system in adults and children and are a genetic and phenotypic heterogeneous group. Large multi-institutional studies and The Cancer Genome Atlas have provided firm insights into the basic genetic drivers in gliomas. The main molecular biomarkers routinely applied to evaluate diffuse gliomas include MGMTpromoter methylation, EGFRalterations (eg, EGFRvIII), IDH1or IDH2mutations, and 1p19q co-deletion. Many of these markers have become standard of care for molecular testing and prerequisites for clinical trial enrollment. Other recent biomarkers include TERTpromoter and ATRXmutations, alterations that identify specific molecular subgroups of diffuse gliomas with biological and clinical relevance. It has also become apparent that distinctive patterns of molecular genetic evolution develop in the context of current therapeutic regimens. Important insights have also been uncovered in the field of pediatric glioma, including the identification of recurrent mutation, fusion, and/or duplication events of the BRAF, FGFR1, MYB, and MYBL1genes in pediatric low-grade gliomas, mutations affecting histone components (H3F3Ap.K27M or p.G34) in pediatric high-grade gliomas, and aggressive subsets developing in midline central nervous system structures. Here, we summarize current concepts in molecular testing for glial tumors, including recent findings by large-scale discovery efforts and technologic advances that are affecting routine diagnostic work.

Glioblastoma multiforme is a heterogeneous and infiltrative cancer with dismal prognosis. Studying the migratory behavior of tumor-derived cell populations can be informative, but it places a high premium on the precision of in vitro methods and the relevance of in vivo conditions. In particular, the analysis of 2D cell migration may not reflect invasion into 3D extracellular matrices in vivo. Here, we describe a method that allows time-resolved studies of primary cell migration with single-cell resolution on a fibrillar surface that closely mimics in vivo 3D migration. We used this platform to screen 14 patient-derived glioblastoma samples. We observed that the migratory phenotype of a subset of cells in response to platelet-derived growth factor was highly predictive of tumor location and recurrence in the clinic. Therefore, migratory phenotypic classifiers analyzed at the single-cell level in a patient-specific way can provide high diagnostic and prognostic value for invasive cancers.

Angiocentric gliomas are pediatric low-grade gliomas (PLGGs) without known recurrent genetic drivers. We performed genomic analysis of new and published data from 249 PLGGs, including 19 angiocentric gliomas. We identified MYB-QKI fusions as a specific and single candidate driver event in angiocentric gliomas. In vitro and in vivo functional studies show that MYB-QKI rearrangements promote tumorigenesis through three mechanisms: MYB activation by truncation, enhancer translocation driving aberrant MYB-QKI expression and hemizygous loss of the tumor suppressor QKI. To our knowledge, this represents the first example of a single driver rearrangement simultaneously transforming cells via three genetic and epigenetic mechanisms in a tumor.

Background:Patients with xeroderma pigmentosum (XP) are strongly predisposed to the development of numerous cutaneous cancers. However, the extent of ocular pathology in these patients has not been adequately studied. Methods:We conducted a retrospective study of tumors involving the ocular surface and ocular adnexa from 6 XP patients. Histopathological evaluation and immunohistochemistry was performed using antibodies directed against the most common mutated proteins in XP (XPA, XPC, and XPD). Results:Patients included 4 males and 2 females with a mean age of 20.8 years (range 10-31) who met the clinical criteria for XP and were found to have a total of 13 neoplasms involving the ocular surface and adnexal skin; 6 squamous cell carcinomas (SCC), 3 cases of conjunctival intraepithelial neoplasia, 2 malignant melanomas, 1 basal cell carcinoma, and 1 atypical fibroxanthoma. Complete XPD loss was present in two tumors from 1 patient, suggesting a germline defect, and in the invasive component of an SCC from a second patient, suggesting a somatic alteration. No clear pattern of loss for XPA or XPC was evident. Conclusions:Our study outlines our early experience with the pathology of ocular neoplasms in XP patients. These findings deserve further exploration with genetic studies and additional patients.

Biodegradable polymeric nanoparticles have the potential to be safer alternatives to viruses for gene delivery; however, their use has been limited by poor efficacy in vivo. In this work, we synthesize and characterize polymeric gene delivery nanoparticles and evaluate their efficacy for DNA delivery of herpes simplex virus type I thymidine kinase (HSVtk) combined with the prodrug ganciclovir (GCV) in a malignant glioma model. We investigated polymer structure for gene delivery in two rat glioma cell lines, 9L and F98, to discover nanoparticle formulations more effective than the leading commercial reagent Lipofectamine 2000. The lead polymer structure, poly(1,4-butanediol diacrylate-co-4-amino-1-butanol) end-modified with 1-(3-aminopropyl)-4-methylpiperazine, is a poly(β-amino ester) (PBAE) and formed nanoparticles with HSVtk DNA that were 138 ± 4 nm in size and 13 ± 1 mV in zeta potential. These nanoparticles containing HSVtk DNA showed 100% cancer cell killing in vitroin the two glioma cell lines when combined with GCV exposure, while control nanoparticles encoding GFP maintained robust cell viability. For in vivoevaluation, tumor-bearing rats were treated with PBAE/HSVtk infusion viaconvection-enhanced delivery (CED) in combination with systemic administration of GCV. These treated animals showed a significant benefit in survival (p= 0.0012 vscontrol). Moreover, following a single CED infusion, labeled PBAE nanoparticles spread completely throughout the tumor. This study highlights a nanomedicine approach that is highly promising for the treatment of malignant glioma.

Oligodendrogliomas are an important adult form of diffuse gliomas with a distinctive clinical and genetic profile. Histologically similar tumors occurring rarely in children are incompletely characterized. We studied 50 patients with oligodendrogliomas (median age at diagnosis 8 y, range 7 mo to 20 y). Tumors resembling dysembryoplastic neuroepithelial tumors or pilocytic astrocytomas or those having a “mixed” histology were excluded. Tumors at first diagnosis were low grade (n=38) or anaplastic (n=12). Histologic features included uniform round cells with perinuclear halos (100), secondary structures (predominantly perineuronal satellitosis) (90), calcifications (46), and microcysts (44). Sequential surgical specimens were obtained in 8 low-grade oligodendroglioma patients, with only 1 progressing to anaplasia. Studies for 1p19q performed in 40 cases demonstrated intact 1p19q loci in 29 (73), 1p19q codeletion in 10 (25), and 1p deletion with intact 19q in 1 (2). Except for 2 young patients (3 and 11 y of age), patients with 1p19q codeletion were older than 16 years at diagnosis. Mutant IDH1 (R132H) protein immunohistochemistry was positive in 4 (of 22) (18) cases, 3 of which also had 1p19q codeletion, whereas 1p19q status was not available on the fourth case. There was a nonsignificant trend for worse overall survival in grade III tumors, but no significant association with age, extent of resection, or 1p19q status. In summary, oligodendrogliomas with classic histology occur in the pediatric population but lack 1p19q codeletion and IDH1 (R132H) mutations in most instances. They are predominantly low grade, recurclinically progress in a subset, but demonstrate a relatively low frequency of histologic progression.

Neurofibromatosis type 1 (NF1) is an autosomal dominant genetic syndrome associated with numerous neoplastic and nonneoplastic manifestations affecting a variety of organ systems, including skin, eye, nervous system, skeleton, and endocrine and gastrointestinal tract. The syndrome results from heterozygous germline mutations in the NF1gene encoding for neurofibromin. Somatic inactivation of the remaining NF1gene is a near-universal feature in tumors developing in these patients. Tumors of the nervous system are an important cause of morbidity and mortality in NF1 patients. These include low-grade neoplasms with little malignant potential (eg, pilocytic astrocytomas and localized neurofibromas), premalignant tumors (eg, plexiform neurofibromas), and high-grade malignant tumors (eg, malignant peripheral nerve sheath tumors and high-grade astrocytomas). It is important for pathologists to accurately classify these tumors and to separate atypical from frank malignant changes in surgical specimens. Ancillary techniques may be helpful in the diagnosis of malignant tumors in NF1 patients, including immunohistochemistry for p53 and p16 protein, as well molecular testing for CDKN2Aloss. A subset of tumors occurring in NF1 patients is difficult to classify or may contain hybrid features preventing unequivocal assignment to a single diagnostic category. Occurrence of specific peripheral nerve sheath tumor types, such as deeplarge plexiform neurofibromas and massive soft-tissue neurofibromas, is essentially limited to NF1 patients. Therefore, appropriate recognition of neoplasms occurring in the context of NF1 has important ramifications for clinical management in this unique patient population.

Inflammatory myofibroblastic tumor (IMT) is a distinct mesenchymal neoplasm that arises in the lung, soft tissues and a variety of organs. In the past, morphologic and conceptual overlap with inflammatory pseudotumor, a presumed inflammatory lesion, has been described in the literature. However, demonstration of ALKgene rearrangements in a subset of cases supports the concept of a distinct neoplastic entity. In rare instances, it may involve the central nervous system, and present as a dural based mass mimicking meningioma. IMT has variable clinical behavior but may also behave in a malignant fashion in a proportion of cases. Interestingly, multicentricity has also been described with IMT. We discuss the case of a 30-year old woman who developed a well circumscribed intracranial mass interpreted preoperatively as a meningioma. Histologic examination demonstrated IMT containing an ALKrearrangement. The neoplasm was morphologically similar to a lung neoplasm resected 31 months previously. We use this case study as an opportunity to discuss the differential diagnosis of IMT with a focus on intrancranial locations and useful ancillary techniques in approaching the pathologic diagnosis.

Tumors of the central nervous system are the second most common malignancy in children. In particular, diffuse intrinsic pontine gliomas (DIPGs) are aggressive tumors with poor prognosis and account for 10 to 25 of pediatric brain tumors. The majority of DIPGs are astrocytic, infiltrative, and localized to the pons. Studies have shown median survival times of less than a year, with 90 of children dying within 2 years. We built multitissue arrays with 24 postmortem DIPG samples and analyzed the morphology and expression of several proteins (p53, EGFR, GFAP, MIB1, BMI1, -catenin, p16, Nanog, Nestin, OCT4, OLIG2, SOX2) with the goal of identifying potential treatment targets and improving our understanding of the biology of these tumors. The majority of DIPGs were high-grade gliomas (22), with 18 cases having features of glioblastoma (World Health Organization WHO grade IV) and 4 cases with high-grade features consistent with anaplastic astrocytoma (WHO grade III). One case was low grade (WHO grade II), and 1 case showed intermediate features between a grade II and grade III glioma (low mitotic rate but increased cellularity and cell atypia), being difficult to grade precisely. The majority of the tumors were positive for GFAP (2424), MIB1 (2324), OLIG2 (2224), p16 (2024), p53 (2024), SOX2 (1924), EGFR (1624), and BMI1 (924). Our results suggest that dysregulation of EGFR and p53 may play an important role in the development of DIPGs. The majority of DIPGs express stem cell markers such as SOX2 and OLIG2, consistent with a role for tumor stem cells in the origin and maintenance of these tumors. Targeted therapies against these proteins could be beneficial in treatment.

Oligodendroglial tumors, which encompass pure oligodendroglioma and mixed oligoastrocytoma, represent the second most common glioma in adults after glioblastoma. They remain controversial neoplasms in the realm of surgical neuropathology. The early recognition of their more favorable prognosis and responsiveness to treatment when compared with diffusely infiltrating astrocytomas has influenced the pathologic diagnostic interpretation, and resulted in a pervasive interobserver variability. The more recent finding of an increased frequency of 1p/19q deletion in these tumors by cytogenetic analysis, and the association of this molecular abnormality with a better prognosis has greatly impacted the field of neuro-oncology. In this review, we focus on important histopathologic aspects in the evaluation of oligodendroglial tumors, key differential diagnoses, and highlight particular clinical and molecular characteristics, as well as current diagnostic and conceptual controversies.

The behavior of rhabdoid meningiomas otherwise lacking malignant features remains unknown as most of the originally reported aggressive cases showed anaplastic histologic features independently of rhabdoid phenotype. We studied 44 patients with rhabdoid meningiomas lacking anaplastic features. Median age at diagnosis was 48.6 years (range 10–79). Location was supratentorial in 28 (63.6%), skull base in 15 (34.1%), and spinal in 1 (2.3%). Tumor grade was otherwise World Health Organization grade I (n = 22, 50%) or II (n = 22, 50%). Rhabdoid cells represented <20% of the tumor in 12 cases (27.3%), 20% to 50% in 18 (40.9%), and >50% in 14 (31.8%). Median clinical follow-up, available for 38 patients, was 5.0 years (range 0.17–14.2). Recurrence occurred in 9 patients (5-year recurrence-free survival, 73.7%) with a significantly higher risk in subtotally resected tumors (p = 0.043). Rhabdoid cell percentage was not associated with recurrence. Six patients died (4 of disease, 2 of unclear causes); 5-year overall survival was 86.7%, a mortality in excess of that expected in grade I–II meningiomas but much lower than originally reported. Review of 50 similar previously reported cases confirmed our findings. We suggest that rhabdoid meningiomas be graded analogously to nonrhabdoid tumors, with caution that some may still behave aggressively and close follow-up is recommended.

Optical coherence tomography (OCT) can distinguish cancer from noncancer tissue in vivo in rodent models of human brain cancer and ex vivo in fresh human brain cancer specimens with high sensitivity and specificity.

Pilocytic astrocytoma (PA) is the most common primary brain tumor in children; various signaling pathways have been implicated in its biology. The Notch signaling pathway has been found to play a role in the development, stem cell biology, and pathogenesis of several cancers, but its role in PA has not been investigated. We studied alterations in Notch signaling components in tumor tissue from 18 patients with PA and 4 with other low-grade astrocytomas to identify much needed therapeutic targets. We found that Notch pathway members were overexpressed at the mRNA (NOTCH1, NOTCH2, HEY1, HEY2) and protein (HES1) levels in PAs at various anatomic sites compared with non-neoplastic brain samples. These changes were not associated with specific BRAF alterations. Inhibiting the Notch pathway in the pediatric low-grade astrocytoma cell lines Res186 and Res259 using either RNA interference or a γ-secretase inhibitor resulted in variable, but significant, reduction in cell growth and migration. This study suggests a potential role for Notch signaling in pediatric low-grade astrocytoma tumorigenesis and that Notch signaling may be a viable pathway therapeutic target.

Optic pathway gliomas represent a specific subtype of astrocytoma with unique clinicopathologic and biologic properties, but studies of tumors in the optic nerve proper have been hampered by limited tissue availability. We analyzed optic nerve gliomas of 59 patients (median age, 9 years; range, 3 months-66 years; 33 female, 26 male) using formalin-fixed paraffin-embedded material in tissue microarrays. Seven patients had the clinical diagnosis of neurofibromatosis type 1 (NF1). Fluorescence in situ hybridization studies were performed for BRAF, PTEN, CDKN2A(p16),and NFLImmunohistochemistry was performed for glial fibrillary acidic protein, phospho-ERK, and mutant IDH1R132H protein. The BRAFduplication was present in 11 (73%) of 15 evaluable tumors, including 1 NF1 patient (1 of 4 tested; 25%). The single tumor lacking BRAFduplication or NF1 association had histologic features of a ganglioglioma. Conversely, heterozygous PTENdeletions were present in 2 (8%) of 25 evaluable cases, one of which was BRAFduplicated and the other was NF1 associated. CDKN2Aand NF1deletions were absent in all tumors tested. Phospho-ERK immunoreactivity was present in 55 (96%) of 57 tumors and was mostly strong and diffuse (80%). Only 1 case of 53 expressed IDH1R132H. Thus, optic nerve gliomas demonstrated molecular alterations typical of pilocytic astrocytomas, including the universal presence of either BRAFduplication or NF1 association and common mitogen-activated protein kinase pathway activation but very rare mutant IDH1 expression.

Cerebellar low-grade astrocytomas with a diffuse pattern of growth are uncommon, comprising World Health Organization (WHO) grade II diffuse astrocytomas (DA) and a minority of WHO grade I pilocytic astrocytomas (PA), so-called PA, “diffuse variant.” Among 106 cerebellar low-grade astrocytomas (WHO grade I and II) operated on at the Mayo Clinic (1984–2010), we identified 19 such cases: 8 PA, “diffuse variant,” 5 DA, and 6 that we were unable to classify further (low-grade astrocytomas, subtype indeterminate). We characterized these tumors using immunohistochemistry and currently available molecular markers (IDH1/2 mutations and BRAF mutation/fusion gene status) and investigated whether the markers could be used to aid the diagnostic process in combination with the clinical and pathologic features. KIAA1549-BRAF fusion was detected in 4 PA, “diffuse variant,” 2 DA, and 2 low-grade astrocytomas, subtype indeterminate, indicating that these tumors were molecularly consistent with PA, the most common subtype of the series. A BRAF V600E mutation was detected in 1 PA, “diffuse variant” case; an IDH1 R132G mutation was found in 1 DA case. These results suggest that KIAA1549-BRAF fusion status and IDH1/2 and BRAF V600E mutational analyses may assist in the histologic classification of this diagnostically challenging group of tumors and result in a more accurate and objective combined molecular and histologic classification.