Targeted fusion analysis can aid in the classification and treatment of pediatric glioma, ependymoma, and glioneuronal tumors

BACKGROUND

The use of next-generation sequencing for fusion identification is being increasingly applied and aids our understanding of tumor biology. Some fusions are responsive to approved targeted agents, while others have future potential for therapeutic targeting. Although some pediatric central nervous system tumors may be cured with surgery alone, many require adjuvant therapy associated with acute and long-term toxicities. Identification of targetable fusions can shift the treatment paradigm toward earlier integration of molecularly targeted agents.

METHODS

Patients diagnosed with glial, glioneuronal, and ependymal tumors between 2002 and 2019 were retrospectively reviewed for fusion testing. Testing was done primarily using the ArcherDx FusionPlex Solid Tumor panel, which assesses fusions in 53 genes. In contrast to many previously published series chronicling fusions in pediatric patients, we compared histological features and the tumor classification subtype with the specific fusion identified.

RESULTS

We report 24 cases of glial, glioneuronal, or ependymal tumors from pediatric patients with identified fusions. With the exception of BRAF:KIAA1549 and pilocytic/pilomyxoid astrocytoma morphology, and possibly QKI-MYB and angiocentric glioma, there was not a strong correlation between histological features/tumor subtype and the specific fusion. We report the unusual fusions of PPP1CB-ALK, CIC-LEUTX, FGFR2-KIAA159, and MN1-CXXC5 and detail their morphological features.

CONCLUSIONS

Fusion testing proved to be informative in a high percentage of cases. A large majority of fusion events in pediatric glial, glioneuronal, and ependymal tumors can be identified by relatively small gene panels.

Gliomatosis cerebri in children shares molecular characteristics with other pediatric gliomas

Gliomatosis cerebri (GC), a rare and deadly CNS neoplasm characterized by involvement of at least three cerebral lobes, predominantly affects adults. While a few small series have reported its occurrence in children, little is known about the molecular characteristics of pediatric GC. We reviewed clinical, radiological, and histological features of pediatric patients with primary GC treated at our institution over 15 years. Targeted sequencing of mutational hotspots in H3F3A, IDH1/2, and BRAF, and genome-wide analysis of DNA methylation and copy number abnormalities was performed in available tumors. Thirty-two patients [23 (72 %) with type 1 and 9 (28 %) with type 2 GC] were identified. Median age at diagnosis was 10.2 years (range 1.5-19.1). A median of 4 cerebral lobes (range 3-8) was affected at diagnosis. In addition, symmetrical bithalamic involvement was observed in 9 (28 %) patients. Twenty-two patients (69 %) had an anaplastic astrocytoma. Despite aggressive therapy, only two patients younger than 3 years at diagnosis are long-term survivors. Clustering analysis of methylation array data from 18 cases classified tumors as IDH (n = 3, 17 %), G34 (n = 4, 22 %), mesenchymal (n = 3, 17 %), and RTK I 'PDGFRA' (n = 8, 44 %). No tumors were classified as K27 subgroup. PDGFRA was the most commonly amplified oncogene in 4 of 22 tumors (18 %). H3F3A p.G34 occurred in all cases classified as G34. Two of 3 cases in the IDH subgroup had IDH1 p.R132H. No H3F3A p.K27 M, IDH2 p.R172, or BRAF p.V600E mutations were observed. There was a trend towards improved survival in the IDH subgroup (P = 0.056). Patients with bithalamic involvement had worse outcomes (P = 0.019). Despite some overlap, the molecular features of pediatric GC are distinct from its adult counterpart. Like in adults, the similarity of genetic and epigenetic characteristics with other infiltrative high-grade gliomas suggests that pediatric GC does not represent a distinct molecular entity.

Primary gliomatosis cerebri involving gray matter in pediatrics: a distinct entity? A multicenter study of 14 cases

BACKGROUND AND PURPOSE

Gliomatosis cerebri (GC) is a rare neoplasm including a variety of tumors, with extremely variable evolution and heterogeneity of prognosis. It may appear either de novo or after a focal glioma, involve predominantly the white or the gray matter, and concern either pediatric or adult patients. We focused on primary GC involving exclusively gray matter in a pediatric population in order better to define the presentation and outcome of this disease.

PATIENTS AND METHODS

We reviewed the databases of seven Departments of Pediatric Oncology to identify pediatric cases of GC between 1990 and 2007. Patients were included if they demonstrated a diffuse infiltrative process involving gray matter in magnetic resonance imaging (MRI) and histological tissue analyses, confirming a proliferative glial disorder.

RESULTS

Fourteen patients with a median age of 8 years were identified. Epilepsy was the main presenting symptom. Brain MRI showed a lesion of the temporal and insular cerebral cortex associated with tumoral infiltration of the thalami and the basal ganglia. Histological examination confirmed the diagnosis of high-grade glioma. Prognosis was always very gloomy in the short term, with a median survival of less than a year.

CONCLUSION

This rare entity, whose prognosis is appalling whatever the treatment proposed, should be clearly identified within the heterogeneous group of GC in the same way as diffuse intrinsic pontine gliomas have been identified among brain stem tumors. Systematic biopsies appear essential to permit the molecular studies which will assist in guiding the choice of future targeted treatments.

Evaluation of molecular genetic alterations associated with tumor progression in a case of gliomatosis cerebri

Gliomatosis cerebri (GC) is a rare tumor characterized by widespread infiltration of the brain and spinal cord. Although GC usually demonstrates histomorphological features of a low-grade tumor, the formation of secondary highly malignant tumor regions may occur. In order to reveal molecular genetic changes associated with tumor progression in GC, we analyzed factors known to be associated with malignant progression in common astocytomas in an unusual GC case of an 18-year-old patient suffering from this disease for almost 7 years. We detected allelic losses in the Rb gene and in exon 4 of the TP53 gene in a tumor region corresponding to a glioblastoma multiforme. EGFR or MDM2 gene amplifications were absent, and no PTEN mutation or allelic loss on chromosome 10 could be detected. Moreover, compared to tumor-free brain tissue of this patient, tumor regions showed increased EGFR expression. These findings show that malignant progression in GC might be associated with the acquisition of molecular genetic changes also found in low-grade astrocytomas with progression to secondary glioblastoma. These data support the notion that GC can be regarded as a subtype of a common astrocytoma.

Nestin expression in neuroepithelial tumors

Nestin is a marker of early stages of neurocytogenesis. It has been studied in 50 neuroepithelial tumors, mostly gliomas of different malignancy grades, by immunohistochemistry, immunofluorescence, immunoblotting, and confocal microscopy and compared with GFAP and Vimentin. As an early marker of differentiation, Nestin is almost not expressed in diffuse astrocytomas, variably expressed in anaplastic astrocytomas and strongly and irregularly expressed in glioblastomas. Negative in oligodendrogliomas, it stains ependymomas and shows a gradient of expression in pilocytic astrocytomas. In glioblastomas, Nestin distribution does not completely correspond to that of GFAP and Vimentin with which its expression varies in tumor cells in a complementary way, as confirmed by confocal microscopy. Tumor cells can thus either derive from or differentiate toward the neurocytogenetic stages. Hypothetically, they could be put in relation with radial glia where during embriogenesis the three antigens are successively expressed. Completely negative cells of invasive or recurrent glioblastomas may represent malignant selected clones after accumulation of mutations or early stem cells not expressing antigens.

Chromosomal abnormalities subdivide neuroepithelial tumors into clinically relevant groups

Gliomas are the most common primary brain tumor, and are histopathologically classified according to their cell type and the degree of malignancy. However, sometimes diagnosis can be controversial,and tumors of the same entity possibly have a wide range of survival. Genetic analysis of these tumors is considered to have great importance in terms that it can provide clinically relevant classification of the tumors and compensate for the limitation of the histological classification. Previous studies using comparative genomic hybridization (CGH) demonstrated that copy number aberrations(CNAs) were frequently recognized in these tumors, and revealed that a gain on chromosomal arm 7q was the most common CNA in diffuse astrocytomas, whereas a small population of the tumor showed losses on 1p/19q which characterizes oligodendrogliomas with good responsiveness to chemotherapeutic regime using procarbazine, nitrosourea and vincristine. High grade (malignant) gliomas(i.e. anaplastic astrocytomas, anaplastic oligodendrogliomas and glioblastomas) have been reported to have a gain on 7p and losses on 9p and 10q. In case of ependymomas, frequent chromosomal aberrations in intracranial tumors were a gain on 1q and losses on 6q, and, on the other hand, a gain on chromosome 7 was recognized almost exclusively in spinal cord tumors. These data suggest that intracranial and spinal cord ependymomas are different genetic diseases and comprise different subgroups within one histological entity. In conclusion, genetic analysis of gliomas may help to classify these tumors and provide leads concerning their initiation and progression. The relationship of these aberrations to patient outcome needs to be addressed.

Molecular genetic alterations in gliomatosis cerebri: what can we learn about the origin and course of the disease?

Gliomatosis cerebri (GC) is a neuroepithelial neoplasm with extensive infiltration of large parts of the brain. Recent data showing the involvement of TP53 mutation or nuclear protein accumulation in some cases have linked the astrocytic phenotype of the tumor cells to TP53 alterations frequently found in common astrocytomas. However, the frequency of these alterations is low, and other molecular genetic changes have been only rarely identified. Those found in common high-grade astrocytomas and glioblastomas are usually missing in GC. The distribution of TP53 point mutations, as well as non-coding polymorphic markers and some cytogenetic data, support a monoclonal origin in some cases, and are at least compatible with it in most cases, while no conclusive data suggesting a polyclonal origin have been reported. This raises the question of mechanisms responsible for the enhanced infiltrative potential of the tumor cells in this disease, which have not yet been identified.

Microtubule-associated protein-2 immunoreactivity: a useful tool in the differential diagnosis of low-grade neuroepithelial tumors

Complex and variable morphological phenotypes pose a major challenge to the histopathological classification of neuroepithelial tumors. This applies in particular for low-grade gliomas and glio-neuronal tumors. Recently, we and others have identified microtubule-associated protein-2 (MAP2) as an immunohistochemical marker expressed in the majority of glial tumors. Characteristic cell morphologies can be recognized by MAP2 immunoreactivity in different glioma entities, i.e., process sparse oligodendroglial versus densely ramified astrocytic elements. Here, we describe MAP2-immunoreactivity patterns in a large series of various neuroepithelial tumors and related neoplasms (n = 960). Immunohistochemical analysis led to the following conclusions: (1) specific pattern of MAP2-positive tumor cells can be identified in 95% of glial neoplasms; (2) ependymal tumors do not express MAP2 in their rosette-forming cell component; (3) tumors of the pineal gland as well as malignant embryonic tumors are also characterized by abundant MAP2 immunoreactivity; (4) virtually no MAP2 expression can be observed in the neoplastic glial component of glio-neuronal tumors, i.e. gangliogliomas; (5) malignant glial tumor variants (WHO grade III or IV) exhibit different and less specific MAP2 staining patterns compared to their benign counterparts (WHO grade I or II); (6) with the exception of melanomas and small cell lung cancers, MAP2 expression is very rare in metastatic and non-neuroepithelial tumors; (7) glial MAP2 expression was not detected in 56 non-neoplastic lesions. These data point towards MAP2 as valuable diagnostic tool for pattern recognition and differential diagnosis of low-grade neuroepithelial tumors.

Various findings in surgically treated epilepsy patients with dysembryoplastic neuroepithelial tumors in comparison with those of patients with other low-grade brain tumors and other neuronal migration disorders

PURPOSE

To determine whether dysembryoplastic neuroepithelial tumors (DNTs) that belong to the neuronal migration disorders (NMDs) are to be classified with them or with "other low-grade brain tumors" regarding several etiologic, clinical, magnetic resonance imaging (MRI), and EEG findings.

METHODS

These findings of 21 DNT patients were compared with those of 13 consecutive patients with other low-grade brain tumors and 41 NMD patients.

RESULTS

The result is absolutely clear: nearly all findings in DNT patients (complications during pregnancy, birth, the newborn period and the postnatal period, age at first seizure, epileptic syndrome, seizure type, febrile seizures, retarded milestones, intellectual and neurologic deficits, MRI, interictal and ictal EEG findings) being similar or in agreement with those of other low-grade brain tumors, not with those of other NMDs.

CONCLUSIONS

Regarding various clinical features including surgery outcome, MRI, and EEG findings, DNTs should be classified with the other low-grade brain tumors, rather than with NMDs.

Comparison of occurrence of oro-maxillo-facial tumor types in different regions of the People's Republic of China

The frequencies of oro-maxillo-facial tumors, by type, seen at the Guangxi Medical College Hospital were surveyed in order to compare different regions of the People's Republic of China. Computer analysis was performed on data for all oro-maxillo-facial tumors, as confirmed by the hospital between 1957 and 1987, inclusive. The results were then used in a comparative study with those of five other medical colleges. Among a total of 4,052 cases, there were 1,593 benign tumors, 2,049 malignant tumors and 410 unknown tumors. Tumors derived from the epithelium were the most common type (42.0% of the total), whereas in the other five medical colleges the mean corresponding proportion was 27.8%, the difference being significant (p < 0.05). Epithelial tumors were also the most common type of malignant tumor (70.5% of the total), whereas the corresponding proportion reported by the other five institutions was 60.6%, which was also significantly different (p < 0.05). The proportion of malignant tumors among the total was more than 50.6%, which was higher than that reported by the other five colleges. This study shows that epithelium-derived tumors and malignant tumors were encountered more frequently at Guangxi Medical College than at the other five medical colleges in China.

Dysembryoplastic neuroepithelial tumors: nonspecific histological forms -- a study of 40 cases

OBJECTIVE

To demonstrate that DNTs include a large morphological spectrum of tumors that cannot be histologically distinguished from conventional categories of gliomas.

METHODS

All tumors from patients who underwent epilepsy surgery in Sainte-Anne hospital (Paris) that histologically resembled gliomas and did not conform to current histological criteria for DNTs or gangliogliomas were entered in the study.

RESULTS

According to the WHO histological classification, the 40 tumors resembled: pilocytic astrocytomas (4 cases), astrocytomas (16 cases), anaplastic astrocytoma (1 case), oligodendrogliomas (10 cases), oligo-astrocytomas (8 cases) or anaplastic oligo-astrocytomas (1 case). However foci of cortical dysplasia could be observed in 47% of the cases. Clinical presentation and imaging features were strikingly similar to that observed in typical DNTs. Although surgical removal was incomplete in 28% of the cases and none of the patients underwent chemo or radiotherapy, none of the tumors recurred (mean follow-up: 7 years). Moreover, serial preoperative imaging in 26 patients (mean follow-up: 4.5 years) demonstrated that these lesions were perfectly stable.

CONCLUSIONS

Whatever the histological appearance of a glial tumor, the diagnosis of DNT must be considered when all the following criteria are associated: (1) partial seizures, with or without secondary generalization, beginning before the age 20 years, (2) no neurological deficit or stable congenital deficit, (3) cortical topography of the lesion as better demonstrated by MRI and (4) no mass effect on imaging.

[The revised WHO classification of brain tumors. Radiological aspects of 4 new tumor entities]

PURPOSE

Characterisation of the classification of brain tumours authorized by the WHO.

METHOD OF APPRAISAL

This classification was revised and published in its second version. In the revision, some tumours were regrouped histogenetically and some tumour variants were added. Radiologically relevant changes of the classification include the differentiation of four new tumour entities that are easily distinguished by MR imaging. These four tumours belong to the group of childhood tumours or tumours occurring in early adulthood and are characterized by a good prognosis after extirpation.

RESULTS OF APPRAISAL

Central neurocytomas are small-cyst ventricular tumours associated with the foramen of Monroi and show moderate contrast enhancement. Infantile desmoplastic gangliogliomas/astrocytomas commonly consist of a solid tumour portion related to the leptomeninges with pronounced contrast enhancement and a typically very large cyst. Pleomorphic xanthoastrocytomas are circumscribed cortical tumours and usually show very moderate gyriform enhancement with only slight signs of a mass effect. Dysembryoblastic neuroepithelial tumours, which originate in the cortical/ subcortical region, likewise show no mass effect; they are characterised by thickening of the cortex from surrounding dysplastic tissue and erosion of the calotte.

Nonteratoid medulloepithelioma of the retina with electron microscopic and immunohistochemical characterization

Medulloepitheliomas are rare intraocular tumors, predominant in children, and originate mainly from undifferentiated nonpigmented epithelium of the ciliary body. These tumors rarely involve the optic nerve or the retina. They are classified as nonteratoid and teratoid types; the latter contains heterologous tissues. The teratoid variant of medulloepitheliomas involving the optic nerve or the retina is reported in four patients only. We describe the first case of a benign nonteratoid medulloepithelioma of the retina in a 3 1/2-year-old girl with immunohistochemical and electron microscopic characterization.