Molecular characterization of disseminated pilocytic astrocytomas

Abstract

Aim: Pilocytic astrocytomas represent the most common paediatric tumours of the central nervous system. Dissemination through the ventricular system occurs rarely in patients with pilocytic astrocytomas; however, it is more common in infants with diencephalic tumours, and is associated with a poor outcome. Despite histological similarities with classic pilocytic astrocytomas, it is still unclear whether disseminated pilocytic astrocytomas may have specific molecular features.

Methods: Seventeen disseminated pilocytic astrocytomas were investigated using the molecular inversion probe array and screened for the presence of gene fusions (KIAA1549-BRAF) and mutations (BRAF, RAS and FGFR1).

Results: Along with evidence of a constitutive MAPK activation in all cases, the molecular inversion probe array, fluorescence in situ hybridization analysis and mutational study revealed KIAA1549-BRAF fusions in 66% and BRAF(V600E) mutations in 5% of cases. No KRAS, HRAS, NRAS or FGFR1 mutations were found.

Conclusions: disseminated pilocytic astrocytomas showed genetic features similar to classic pilocytic astrocytoma, including a similar incidence of KIAA1549-BRAF fusions, BRAF mutations and a stable genetic profile. Given common activation of the MAPK pathway, the use of specific inhibitors can be hypothesized for the treatment of disseminated pilocytic astrocytomas, along with standard chemo- and/or radiotherapy.

Keywords: BRAF; ERK; KIAA1549-BRAF fusion; MAPK pathway; disseminated pilocytic astrocytoma; low grade gliomas.