Search

Fusions involving CRAF (RAF1) are infrequent oncogenic drivers in pediatric low-grade gliomas, rarely identified in tumors bearing features of pilocytic astrocytoma, and involving a limited number of known fusion partners. We describe recurrent TRAK1::RAF1 fusions, previously unreported in brain tumors, in three pediatric patients with low-grade glial-glioneuronal tumors. We present the associated clinical, histopathologic and molecular features. Patients were all female, aged 8 years, 15 months, and 10 months at diagnosis. All tumors were located in the cerebral hemispheres and predominantly cortical, with leptomeningeal involvement in 2/3 patients. Similar to previously described activating RAF1 fusions, the breakpoints in RAF1 all occurred 5' of the kinase domain, while the breakpoints in the 3' partner preserved the N-terminal kinesin-interacting domain and coiled-coil motifs of TRAK1. Two of the three cases demonstrated methylation profiles (v12.5) compatible with desmoplastic infantile ganglioglioma (DIG)/desmoplastic infantile astrocytoma (DIA) and have remained clinically stable and without disease progression/recurrence after resection. The remaining tumor was non-classifiable; with focal recurrence 14 months after initial resection; the patient remains symptom free and without further recurrence/progression (5 months post re-resection and 19 months from initial diagnosis). Our report expands the landscape of oncogenic RAF1 fusions in pediatric gliomas, which will help to further refine tumor classification and guide management of patients with these alterations., (© 2023 The Authors. Brain Pathology published by John Wiley & Sons Ltd on behalf of International Society of Neuropathology.)

The 2021 5th edition of the WHO Classification of Tumors of the Central Nervous System reflects the discovery of genetic alterations underlying many central nervous system (CNS) neoplasms. Insights gained from technologic advances and novel applications in molecular diagnostics, including next-generation sequencing and DNA methylation-based profiling, coupled with the recognition of clinicopathologic correlates, have prompted substantial changes to CNS tumor classification; this is particularly true for pediatric low-grade gliomas and glioneuronal tumors (pLGG/GNTs). The 2021 WHO now classifies gliomas, glioneuronal tumors and neuronal tumors into 6 families, three of which encompass pLGG/LGNTs: "Pediatric type diffuse low-grade gliomas," "circumscribed astrocytic gliomas," and "glioneuronal and neuronal tumors." Among these are six newly recognized tumor types: "diffuse astrocytoma, MYB or MYBL1-altered"; "polymorphous low grade neuroepithelial tumor of the young (PLNTY)"; "diffuse low-grade glioma-MAPK altered"; "Diffuse glioneuronal tumor with oligodendroglioma-like features and nuclear clusters (DGONC)"; "myxoid glioneuronal tumor (MGT)"; and "multinodular and vacuolating neuronal tumor (MVNT)." We review these newly recognized entities in the context of general changes to the WHO schema, discuss implications of the new classification for treatment of pLGG/LGNT, and consider strategies for molecular testing and interpretation., (© 2022 The Authors. Brain Pathology published by John Wiley & Sons Ltd on behalf of International Society of Neuropathology.)

Myxopapillary ependymomas (MPE) are considered benign (World Health Organization (WHO) grade I) neoplasms with favorable prognosis. However, malignant behavior occurs in a small subset. To our knowledge, only five anaplastic MPEs have been reported without consensus on diagnostic criteria. We retrieved 14 anaplastic MPEs from the pathology archives of six institutions. Each tumor included at least two of the following features: ≥5 mitoses per 10 high power fields, Ki-67 labeling index (LI) ≥10%, microvascular proliferation (MVP) and spontaneous necrosis. These features were typically encountered in the foci of hypercellularity and reduced mucin. There were eight male and six female patients (age range 6-57 years, median = 16.5). Ten tumors displayed anaplasia at initial resection, and 4 were anaplastic at a second surgery for recurrence (ranging from 9 months to 14 years following initial resection). The Ki-67 LI ranged between 8% and 40% in the anaplastic foci and <3% in the foci of classic MPE. There was documented cerebrospinal fluid (CSF) dissemination in seven cases, recurrence following an anaplastic diagnosis in three cases and bone or soft tissue invasion in two cases. One patient suffered lung metastases. Two cases evaluated by targeted next-generation sequencing and one evaluated by fluorescence in situ hybridization (FISH) showed nonspecific chromosomal gains. We conclude that although rare, anaplastic MPE occurs in both pediatric and adult patients, similar to other ependymomas. At a minimum, closer follow-up is recommended, given the concern for aggressive biologic potential. Further study is needed to determine WHO grading criteria and genetic indicators of tumor progression., (© 2018 International Society of Neuropathology.)

We report 10 cases of a non-neurocytic, purely neuronal tumor affecting adults. Situated in the cerebral hemispheres, with 7 of 10 confined to the temporal lobes, most presented with seizures as their principal clinical manifestations. On magnetic resosnance imaging (MRI), the tumors generally appeared solid and non-contrast enhancing with minimal diffuse infiltration, edema, or mass effect. Six examples demonstrated internal nodularity. Microscopically, the tumor cells were largely distributed into discrete and coalescent nodules exhibiting varying degrees of matrix vacuolization, principally within the deep cortical ribbon and superficial subcortical white matter. Populating elements ranged from morphologically ambiguous to recognizably neuronal, with only two cases manifesting overt ganglion cell cytology. In all cases, tumor cells exhibited widespread nuclear immunolabeling for the HuC/HuD neuronal antigens, although expression of other neuronal markers, including synaptophysin, neurofilament and chromogranin was variable to absent. Tumor cells also failed to express GFAP, p53, IDH1 R132H, or CD34, although CD34-labeling ramified neural elements were present in the adjoining cortex of seven cases. Molecular analysis in a subset of cases failed to reveal DNA copy number abnormalities or BRAF V600E mutation. Follow-up data indicate that this unusual neuronal lesion behaves in benign, World Health Organization (WHO) grade I fashion and is amenable to surgical control., (© 2013 International Society of Neuropathology.)

Central nervous system neoplasms with combined features of malignant glioma and primitive neuroectodermal tumor (MG-PNET) are rare, poorly characterized, and pose diagnostic as well as treatment dilemmas. We studied 53 MG-PNETs in patients from 12 to 80 years of age (median = 54 years). The PNET-like component consisted of sharply demarcated hypercellular nodules with evidence of neuronal differentiation. Anaplasia, as seen in medulloblastomas, was noted in 70%. Within the primitive element, N-myc or c-myc gene amplifications were seen in 43%. In contrast, glioma-associated alterations involved both components, 10q loss (50%) being most common. Therapy included radiation (78%), temozolomide (63%) and platinum-based chemotherapy (31%). Cerebrospinal fluid (CSF) dissemination developed in eight patients, with response to PNET-like therapy occurring in at least three. At last follow-up, 27 patients died, their median survival being 9.1 months. We conclude that the primitive component of the MG-PNET: (i) arises within a pre-existing MG, most often a secondary glioblastoma; (ii) may represent a metaplastic process or expansion of a tumor stem/progenitor cell clone; (iii) often shows histologic anaplasia and N-myc (or c-myc) amplification; (iv) has the capacity to seed the CSF; and (v) may respond to platinum-based chemotherapy regimens.

The clinical and pathologic features of two glioneuronal neoplasms newly incorporated in the 2007 revision of the WHO classification of nervous system tumors are reviewed. These are the papillary glioneuronal tumor and the rosette-forming glioneuronal tumor of the fourth ventricle.

In recent years, antineuronal autoantibodies of varying antigenic specificity have come to be associated with a number of paraneoplastic neurologic disorders. Anti-Hu is a polyclonal complement-fixing IgG directed against a 35 to 40 kilodalton protein concentrated in the nuclei of neurons throughout the central and peripheral neuraxes. Its elaboration at high titer in serum and cerebrospinal fluid is invariably associated with a neurologic syndrome characterized chiefly by subacutely evolving sensory neuropathy and an array of central disturbances that include bulbar and cerebellar dysfunction, limbic encephalitis and motor neuron disease. The manufacture of anti-Hu IgG is triggered in a great majority of cases by underlying small cell carcinomas of pulmonary origin, typically limited in stage and otherwise silent, that aberrantly express the native neuronal antigen or an antigenically indistinguishable epitope. Both neoplastic and diseased neural tissues contain lymphocytes of B and T lineage specifically cognizant of the Hu antigen as well as concentrated anti-Hu IgG bound to tumor cells and neurons, respectively. These observations suggest that an immune response serving initially to limit the growth and spread of its inciting neoplasm comes subsequently to be misdirected against the nervous system of the host, resulting in autoimmunologically-mediated neurologic injury. Clinical, neuropathologic and immunologic data derived from a series of 71 sero-confirmed cases of the anti-Hu-associated paraneoplastic sensory neuronopathy/encephalomyelitis complex are reviewed.