New IDH1 I113T mutation associated with BRAF V600E mutation: new driver of gliomagenesis?

Implications of BRAF V600E mutation in gliomas: Molecular considerations, prognostic value and treatment evolution

Gliomas are molecularly heterogeneous brain tumors responsible for the most years of life lost by any cancer. High-grade gliomas have a poor prognosis and despite multimodal treatment including surgery, radiotherapy, and chemotherapy, exhibit a high recurrence rate. There is a need for new therapeutic approaches based on precision medicine informed by biomarker assessment and BRAF, a key regulator of MAPK signaling pathway, influencing cell differentiation, proliferation, migration and pro-tumorigenic activity, is emerging as a promising molecular target. V600E, is the most frequent BRAF alteration in gliomas, especially in pediatric low-grade astrocytomas, pleomorphic xanthoastrocytoma, papillary craniopharyngioma, epithelioid glioblastoma and ganglioglioma. The possible application of BRAF-targeted therapy in gliomas is continuously growing and there is preliminary evidence of prolonged disease control obtained by BRAF inhibitors in tumors harboring BRAF V600E mutation. The possibility of introducing targeted therapies into the treatment algorithm represents a paradigm shift for patients with BRAF V600E mutant recurrent high-grade and low-grade glioma and BRAF routine testing should be considered in clinical practice. The focus of this review is to summarize the molecular landscape of BRAF across glioma subtypes and the novel therapeutic strategies for BRAF V600E mutated tumors.

BRAFnon-V600E more frequently co-occurs with IDH1/2 mutations in adult patients with gliomas than in patients harboring BRAFV600E but without a survival advantage

BACKGROUND

The effects of BRAF^non-V600E and BRAF^V600E on the outcomes and the molecular characteristics of adult glioma patients are unknown and need to be explored, although BRAF^V600E has been extensively studied in pediatric glioma.

METHODS

Co-occurring mutations and copy number alterations of associated genes in the MAPK and p53 pathways were investigated using data from The Cancer Genome Atlas (TCGA) public database retrieved by cBioPortal. The prognosis of available adult glioma cohorts with BRAF^V600E and BRAF^non-V600E mutations were also investigated.

RESULTS

Ninety patients with BRAF^V600E or BRAF^non-V600E were enrolled in this study, and data from 52 nonredundant patients were investigated. Glioblastoma multiform was the most common cancer type, with BRAF ^non-V600E and BRAF^V600E. TP53 (56.00% vs. 7.41%), IDH1/2 (36.00% vs. 3.70%), and ATRX (32.00% vs. 7.41%) exhibited more mutations in BRAF^non-V600E than in BRAF^V600E, and TP53 was an independent risk factor (56.00% vs. 7.41%). Both BRAF^non-V600E and BRAF^V600E frequently overlapped with CDKN2A/2B homozygous deletions (HDs), but there was no significant difference. Survival analysis showed no difference between the BRAF ^non-V600E and BRAF^V600E cohorts, even after excluding the survival benefit of IDH1/2 mutations and considering the BRAF^non-V600E mutations in the glycine-rich loop (G-loop) and in the activation segment. The estimated mean survival of patients with BRAF^non-V600E & IDH1/2^WT with mutations in the G-loop groups was the shortest.

CONCLUSIONS

BRAF^non-V600E exhibited a stronger association with IDH1/2 mutations than BRAF^V600E, but no survival advantage was found.

Oligodendroglioma showing pleomorphic xanthoastrocytoma-like perivascular microlesion: With IDH1, TERT promoter mutation and 1p/19q codeletion detected in both components

We report a histological and genetic study of concurrent oligodendroglioma and a microscopic pleomorphic xanthoastrocytoma (PXA)-like lesion in a 48-year-old male. He presented with generalized seizure, and magnetic resonance imaging revealed a nonenhanced left frontal lobe mass suggesting low-grade glioma. The patient underwent craniotomy and tumor resection. Histopathological examination of the surgical specimen showed an oligodendroglioma with a PXA-like element; the latter measured 0.9 mm and occupied a Virchow-Robin space of the superficial cortex. The whole tumor had no elevated mitotic activity, microvascular proliferation or necrosis. Each component was immunohistochemically isocitrate dehydrogenase (IDH1)-R132H positive, p53 negative and ATRX positive. Genetic analyses clarified identical IDH1 G395A mutation, promoter C228T mutation and 1p/19q codeletion in both elements. Careful integration of histology and telomerase reverse transcriptase (TERT) molecular parameters revealed that this case was an oligodendroglioma showing PXA-like features, rather than a collision tumor. This case provides further insights into the gliomagenesis.

Oncogenic BRAF Alterations and Their Role in Brain Tumors

Alterations of the v-raf murine sarcoma viral oncogene homolog B (BRAF) have been extensively studied in several tumor entities and are known to drive cell growth in several tumor entities. Effective targeted therapies with mutation-specific small molecule inhibitors have been developed and established for metastasized malignant melanoma. The BRAF V600E mutation and KIAA1549-BRAF fusion are alterations found in several brain tumors and show a distinct prognostic impact in some entities. Besides the diagnostic significance for the classification of central nervous system tumors, these alterations present possible therapy targets that may be exploitable for oncological treatments, as it has been established for malignant melanomas. In this review the different central nervous system tumors harboring BRAF alterations are presented and the diagnostic significance, prognostic role, and therapeutic potential are discussed.

BRAF V600E, TERT, and IDH2 Mutations in Pleomorphic Xanthoastrocytoma: Observations from a Large Case-Series Study

BACKGROUND

Anaplastic pleomorphic xanthoastrocytoma (PXA) was added to grade III glial tumors as a distinct entity in the 2016 World Health Organization (WHO) classification of tumors of the central nervous system. We retrospectively reviewed and analyzed 55 pathologically confirmed PXA cases according to the newest WHO classification to better clarify the clinical, molecular, and prognostic features of this rare neoplasm.

METHODS

In total, 55 pathologically confirmed PXA cases according to the newest WHO classification were retrospectively reviewed and analyzed. After sequencing for BRAF, TERT, IDH1/2, and H3F3A, survival analysis was performed to determine the factors affecting survival.

RESULTS

The patients with BRAF V600E mutations were generally younger than those without it, although not statistically significant (27.9 ± 15.4 years and 37.1 ± 17.0 years, respectively, P = 0.054). TERT promoter mutation frequency in PXA was lower than in patients with anaplastic PXA although not statistically significant (4.4% and 28.6%, P = 0.083). One instance of PXA with IDH2 mutation, and no IDH1 and H3F3A mutations were found. In terms of prognosis, patients with anaplastic PXA had shorter overall survival and progression-free survival compared with patients with PXA. The subgroup with gross total resection had a longer median OS (not reached vs. 60.0 months, P = 0.0221) and PFS (not reached vs. 60.0 months, P = 0.0232) compared with patients with PXA with subtotal resection.

CONCLUSIONS

The identification of BRAF V600E, TERT, and IDH2 mutations in PXA expands our molecular understanding of PXA. Patients with PXA with gross total resection achieve good outcomes.