A comprehensive analysis identifies BRAF hotspot mutations associated with gliomas with peculiar epithelial morphology

Abstract

Brain tumors harbor various BRAF alterations, the vast majority of which are the BRAF kinase-activating V600E mutation. BRAF mutations are most frequently detected in certain subtypes of low-grade glioma, such as pilocytic astrocytoma (PA), pleomorphic xanthoastrocytoma (PXA), ganglioglioma (GG) and dysembryoplastic neuroepithelial tumor (DNT). However, it is unclear whether gliomas harboring BRAF mutations can be invariably regarded as these glioma subtypes or their derivatives. To address this question, we analyzed 274 gliomas in our institutional case series. We performed high-resolution melting analyses and subsequent direct Sanger sequencing on DNA isolated from snap-frozen tumor tissues. As expected, BRAF mutations were detected in the aforementioned low-grade gliomas: in 4/27 PAs, 2/3 PXAs, 4/8 GGs, and 1/6 DNTs. In addition to these gliomas, 1/2 astroblastomas (ABs) and 2/122 glioblastomas (GBs) harbored BRAF mutations. Pathological investigation of the two GBs revealed that one was a GB displaying epithelial features that presumably arose from a precedent GG, whereas the other GB, which harbored a rare G596 A mutation, showed marked epithelial features, including astroblastic rosettes. Our results indicate that in addition to being present in established BRAF-associated gliomas, BRAF mutations might be associated with epithelial features in high-grade gliomas, including sheet-like arrangement of polygonal tumor cells with a plump cytoplasm and astroblastic rosettes, and thus could potentially serve as a genetic marker for these features.

Pediatric ganglioglioma with an H3 K27M mutation arising from the cervical spinal cord

“…Whereas most GGs histologically correspond to WHO grade I, GGs with anaplastic features are categorized as WHO grade III. 6 The histopathological diagnosis of our patient was GG; however, genetic analyses revealed that the tumor lacked the BRAF V600E mutation but carried the H3F3A K27M mutation. 4 Accordingly, this mutation can be used as a molecular marker and as a potential therapeutic marker for these phenotypes of gliomas.…”

“…6,7 Although IDH1/2 and BRAF V600E mutations were not detected, the H3F3A K27M mutation was clearly evident (Fig. Polymerase chain reaction, Sanger sequencing and high-resolution melting analyses of mutation hotspots on IDH1, IDH2, BRAF and H3F3A were performed as described in our previous study.…”

Insular primary glioblastomas with IDH mutations: Clinical and biological specificities

“…To verify the specificity in genetic backgrounds of IDH ‐mut pGBMs, we analyzed expression of glioma‐related genes. Our previous studies indicated that expression patterns of mesenchymal and proneural marker genes in GBMs can be measured by our original scoring scale, the P‐M score, which is defined by expression levels of six signature genes . As a result, the P‐M score of IDH ‐mutant ( IDH ‐mut) pGBM was significantly higher than that of IDH ‐wildtype ( IDH ‐wt) pGBM (Fig.…”

“…Sampling and DNA preparation were performed as previously described . PCR and sequencing of IDH1, IDH2 and TERT promoter were performed as previously described . The allelic status of chromosomes 1p, 10, 17p and 19q was evaluated by a PCR‐based LOH assay as previously described …”

A case of diffuse midline glioma, H3 K27M mutant mimicking a hemispheric malignant glioma in an elderly patient

“…2,3 Although IDH1/2 and BRAF V600E mutations were not detected, the H3F3A K27M mutation was clearly evident (Fig. Polymerase chain reactions (PCR), Sanger sequencing, and high-resolution melting analyses of mutation hotspots on IDH1, IDH2, TERT, BRAF, and H3F3A were performed as described in our previous study.…”