No significant differences regarding additional imaging features emerged between BRAF V600E-mutant and wild-type lesions, with the exception of the number of tumors with cystic components, significantly higher in BRAF V600E-mutant PAs (p = 0.011) CONCLUSION: Assessment of the DWI characteristics of GGs and PAs may assist in predicting BRAF V600E status, suggesting a radiogenomic correlation and prompt molecular characterization of these tumors.
Both p.V600E mutation and KIAA1549-BRAF fusion have been described in pilocytic astrocytoma (PA) and GG, but they differ with regards to the rates of different BRAF alterations, and careful histological examination is an important component of patho-molecular correlations.
Stratum 1 comprised patients with WHO grade I pilocytic astrocytoma harbouring either one of the two most common BRAF aberrations (KIAA1549-BRAF fusion or the BRAF<sup>V600E</sup> [Val600Glu] mutation).
BRAF-V600E mutations are most commonly found in pleomorphic xanthoastrocytoma, ganglioglioma, epithelioid glioblastoma, and gliomas diagnosed at a younger age; BRAF-KIAA1549 fusion is the most common BRAF alteration in pilocytic astrocytoma.
Histologically, V600E-carrying PA appeared more infiltrative, yet our limited clinical follow-up failed to detect a deleterious prognostic significance.
Aneuploid genomes were identified in 45% of adult compared with 17% of pediatric PA. Gains were non-random, favoring chromosomes 5, 7, 6 and 11 in order of frequency, and preferentially affecting non-cerebellar PA and tumors with BRAF V600E mutations and not with KIAA1549-BRAF fusions or FGFR1 mutations.
This study identified the expression of KIAA1549-BRAF fusion gene and BRAF V600E mutation, mutations at exon 4 of the IDH1 and IDH2 genes in samples of pilocytic astrocytomas (PA) and grade-II astrocytomas (A-II) pediatric patients.
These results suggest that (a) BRAF-KIAA1549 fusion may be common in PAs with atypical clinicoradiologic and histologic features, including those at extracerebellar sites, (b) BRAF V600E mutation is uncommon in extracerebellar PAs, and (c) TP53 mutation analysis remains a valuable tool in identifying childhood gliomas that will likely behave in a malignant fashion.
Recent developments in v-raf murine sarcoma viral oncogene homolog B1 (BRAF)(V600E)-specific small molecule inhibitors and their clinical approval for other cancer types could turn BRAF(V600E) into a promising molecular predictor of outcome in pilocytic astrocytomas, given a treatment with a mutation-specific BRAF inhibitor is applied.
The data further support previous observations that these two alterations of the BRAF, KIAA1549 fusions and V600E point mutations, are associated primarily with pilocytic astrocytomas and nonpilocytic gliomas, respectively.
The high mutation frequencies in pleomorphic xanthoastrocytomas, gangliogliomas and extra-cerebellar pilocytic astrocytomas implicate BRAF (V600E) mutation as a valuable diagnostic marker for these rare tumor entities.
For the first time, we report concomitant presence of a somatic BRAF(V600E) mutation in an NF1 patient indicating that more than one Ras/ERK pathway component can be affected in PA.