Clinicopathological characteristics of circumscribed high-grade astrocytomas with an unusual combination of BRAF V600E, ATRX, and CDKN2A/B alternations

Molecular Heterogeneity in BRAF-Mutant Gliomas: Diagnostic, Prognostic, and Therapeutic Implications

Over the last few decades, deciphering the alteration of molecular pathways in brain tumors has led to impressive changes in diagnostic refinement. Among the molecular abnormalities triggering and/or driving gliomas, alterations in the MAPK pathway reign supreme in the pediatric population, as it is encountered in almost all low-grade pediatric gliomas. Activating abnormalities in the MAPK pathway are also present in both pediatric and adult high-grade gliomas. Across those alterations, BRAF p.V600E mutations seem to define homogeneous groups of tumors in terms of prognosis. The recent development of small molecules inhibiting this pathway retains the attention of neurooncologists on BRAF-altered tumors, as conventional therapies showed no significant effect, nor prolonged efficiency on the high-grade or low-grade unresectable forms. Nevertheless, tumoral heterogeneity and especially molecular alteration(s) associated with MAPK-pathway abnormalities are not fully understood with respect to how they might lead to the specific dismal prognosis of those gliomas and/or affect their response to targeted therapies. This review is an attempt to provide comprehensive information regarding molecular alterations related to the aggressiveness modulation in BRAF-mutated gliomas and the current knowledge on how to use those targeted therapies in such situations.

Acquired ATRX Loss and ALT Phenotype Through Tumor Recurrences in a Case of Pleomorphic Xanthoastrocytoma Suggest Their Possible Roles in Tumor Progression

Pleomorphic xanthoastrocytoma (PXA) is classified as an astrocytic glioma occurring most often in children or young adults. Molecular alterations in PXA are not fully known, especially those associated with tumor progression. We describe a patient with several relapses of a PXA. The tumor showed an acquired ATRX loss through tumor evolution. We tested alternative lengthening of telomeres (ALT) with the C-circle test. While the test was negative in the first tumor, a high circle activity was detected in the last relapse, suggesting an acquired ALT phenotype. Our data not only confirm previous findings of the possible occurrence of ATRX mutations in PXA but also suggest that this alteration is linked to PXA progression. In small biopsies, tumors with ATRX loss, without IDH or histone mutation, pathologists should consider the diagnosis of PXA, especially if associated with BRAF V600E mutation, CDKN2A deletion, and ALT.

Giant cell glioblastoma is a distinctive subtype of glioma characterized by vulnerability to DNA damage

Giant cell glioblastoma (GC-GBM) consists of large cells with pleomorphic nuclei. As a contrast to GC-GBM, we defined monotonous small GBM (MS-GBM) as GBM that consists of small cells with monotonous small nuclei, and compared the DNA damage as well as other pathological features. GC-GBM showed minimal invasion (< 2 mm) and focal sarcomatous areas. TERTp was wild type in GC-GBM but mutant in MS-GBM. OLIG2 expression was significantly higher in MS-GBM (P < 0.01) (77% in MS-GBM and 7% in GC-GBM). GC-GBM showed significantly higher DNA double-strand breaks (DSBs) compared with MS-GBM (P < 0.01) (76% in GC-GBM and 15% in MS-GBM). Nearly, all large cells in GC-GBM underwent DSBs. Thus, significant DSBs in GC-GBM might be induced by an innate lesser stemness characteristic and be followed by mitotic slippage, resulting in polyploidization and the large pleomorphic nuclei. We conclude that GC-GBM is a distinctive subtype of glioma characterized by its vulnerability to DNA damage and that wild-type TERTp and lower OLIG2 function might induce this feature. Notably, even large pleomorphic nuclei with severe DSBs demonstrated Ki67 positivity, which alerts pathologists to the interpretation of Ki67 positivity, because cells with large nuclei undergoing severe DSBs cannot be recognized as proliferating cells that contribute to tumor aggressiveness.

Anaplastic pleomorphic xanthoastrocytoma associated with an H3G34 mutation: a case report with review of literature

Here, we report a rare case of anaplastic pleomorphic xanthoastrocytoma (PXA) associated with an H3G34 mutation. A 12-year-old male presented with loss of appetite, vomiting, headache, and a generalized seizure, and CT revealed a 9.0 cm left frontal lobe mass with some septal walls and a localized high-density area suggestive of hemorrhage or calcification, causing severe midline shift. He emergently underwent subtotal resection and the tumor was morphologically diagnosed as anaplastic PXA. DNA sequencing identified an H3F3A G34R mutation and a TP53 R273H mutation, and immunohistochemically, ATRX nuclear expression was lost. In CNS tumors, H3G34 mutations are essentially detected in glioblastoma (GBM) or central nervous system primitive neuroectodermal tumors. Those tumors most likely comprise a single biological entity (high-grade glioma with H3G34 mutation) because of no significant difference in molecular profiling and prognosis between GBM and PNET morphologies. To our knowledge, our present case is the first one of anaplastic PXA associated with an H3G34 mutation, and whether it biologically corresponds to "high-grade glioma with H3G34 mutation" needs further studies.