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).
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.
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.
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.